An alphabetical guide to astronomical terms. Use the search box or browse by letter to find a definition.
Browse all 88 constellations, or read the guide to their star and deep-sky measurements.
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Search terms, star names, object numbers, abbreviations and definitions. Exact matches appear first. Printing includes the complete glossary.
415 definitions
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How bright a star would appear if placed at a standard distance of 10 parsecs, about 32.6ly. It helps compare intrinsic stellar brightness without the effect of different distances. It is different from apparent magnitude, which describes the view from Earth.
Other names and search terms: AO
Technology that measures atmospheric distortion and rapidly adjusts optical elements, usually a deformable mirror, to sharpen a ground-based telescope's image. It is especially important for high-resolution work and is different from slowly maintaining the large primary mirror's shape.
Sources: NAOJ: adaptive optics at Subaru
Other names and search terms: Einstein
A theoretical physicist whose general theory of relativity describes gravity through the curvature of spacetime. It underpins modern cosmology and predictions about gravitational lensing, black holes and gravitational waves. He is included for his influence on astronomy rather than as an observational astronomer.
| Dates | 1879-1955 |
|---|---|
| Background | German-born physicist; worked in Europe and the United States |
Sources: Official or institutional reference: Albert Einstein
Other names and search terms: Alt-az, Altaz
A mount that moves up and down in altitude and left and right in azimuth. Following an object usually requires adjustments in both axes, either by hand or under computer control.
The angle of an object above the horizon: 0 degrees at the horizon and 90 degrees directly overhead. In this context it describes an angle, not height above sea level.
Other names and search terms: Chained maiden, And
Andromeda is one of the 88 IAU-recognised constellations. Its common English description is: chained maiden.
| Common English name | Chained maiden |
|---|---|
| IAU abbreviation | And |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Mirach (Beta Andromedae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Mirach |
| Latin / catalogue designation | Beta Andromedae |
| Apparent magnitude (V) | 2.05 |
| Spectral type | M0+IIIa |
| Distance from Earth | About 200ly |
| RA (ICRS / J2000) | 01h09m44s |
| Declination (ICRS / J2000) | +35d37m14s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 75 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Mirach
| Role | Nearly equal brightest star |
|---|---|
| Common / proper name | Alpheratz |
| Latin / catalogue designation | Alpha Andromedae |
| Apparent magnitude (V) | 2.06 |
| Spectral type | B8IV-VHgMn |
| Distance from Earth | About 97ly |
| RA (ICRS / J2000) | 00h08m23s |
| Declination (ICRS / J2000) | +29d05m26s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 68 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpheratz
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Almach |
| Latin / catalogue designation | Gamma Andromedae |
| System or component described | Bright primary of the Almach multiple system |
| Apparent magnitude (V) | 2.10 |
| Spectral type | K2+IIb |
| Distance from Earth | About 393ly |
| RA (ICRS / J2000) | 02h03m54s |
| Declination (ICRS / J2000) | +42d19m47s |
| System structure | A hierarchical multiple: the bright star has a fainter companion which itself contains a close triple. |
| Observing interest | A striking golden and blue-white visual pair, usually a rewarding small-telescope target. |
| Visibility from Lewes | Circumpolar from Lewes: remains above the horizon throughout the day and night; needs a dark, clear sky to observe. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate. The position, magnitude and spectral type shown describe the bright primary. Its catalogue parallax gives a rounded distance of about 390ly, with substantial uncertainty; the same distance is adopted for the physical system. The parallax is relatively uncertain, so the distance is especially approximate.
Sources: SIMBAD: Almach; SIMBAD: companion hierarchy; Carro (2011): Almach measurements and hierarchy
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 2.5 million ly |
| RA (J2000; approximate centre) | 00h42m42s |
| Declination (J2000; approximate centre) | +41d16m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 80 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Compact Elliptical Galaxy |
|---|---|
| Distance from Earth | 2.5 million ly |
| RA (J2000; approximate centre) | 00h42m42s |
| Declination (J2000; approximate centre) | +40d52m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 80 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 2,500ly |
| RA (J2000; approximate centre) | 23h25m54s |
| Declination (J2000; approximate centre) | +42d33m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 82 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye. Mirach and Alpheratz are effectively tied near magnitude 2.1; catalogue values and variability can change their order.
Sources: IAU: the 88 constellations
Other names and search terms: Apparent size
How large an object appears as an angle on the sky, rather than its physical diameter. The Sun and Moon have similar angular sizes despite being very different physical sizes.
Other names and search terms: Air pump, Ant
Antlia is one of the 88 IAU-recognised constellations. Its common English description is: air pump.
| Common English name | Air pump |
|---|---|
| IAU abbreviation | Ant |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Alpha Antliae |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Antliae |
| Apparent magnitude (V) | 4.25 |
| Spectral type | K3III |
| Distance from Earth | About 370ly |
| RA (ICRS / J2000) | 10h27m09s |
| Declination (ICRS / J2000) | -31d04m04s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Rises, but very low: maximum altitude about 8 degrees; needs a clear southern horizon. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Antliae
| Object type | Galaxy |
|---|---|
| Distance from Earth | About 51 million ly (redshift-based luminosity distance) |
| RA (J2000; approximate centre) | 09h45m39s |
| Declination (J2000; approximate centre) | -31d11m27s |
| Visibility from Lewes | Rises, but very low: maximum altitude about 8 degrees; needs a clear southern horizon. |
An indicative distance calculated from SIMBAD redshift z=0.003611, using H0=70km/s/Mpc and a flat cosmology with matter density parameter 0.3. This is a luminosity distance, not a direct measurement; local galaxy motions can cause substantial uncertainty, especially at low redshift.
Sources: SIMBAD: NGC 2997
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
The diameter of a telescope's main light-collecting objective lens or primary mirror. A larger aperture collects more light and can resolve finer detail when optical quality and observing conditions allow.
The desire for ever-larger telescopes to collect more light and reveal more detail. Extra aperture also brings practical demands such as greater weight, storage space and a sturdier mount.
The point in an orbit at which a body is farthest from the Sun. For an ideal ellipse, perihelion and aphelion distances are a(1 - e) and a(1 + e), where a is the semi-major axis and e is eccentricity.
The point in an Earth-centred orbit at which the orbiting body is farthest from Earth. The Moon's distance at apogee changes from one orbit to another.
Other names and search terms: AFOV
The angular width of the view presented to your eye by an eyepiece. This is different from the actual patch of sky visible through the telescope.
Other names and search terms: Magnitude, Visual magnitude, V magnitude
A measure of how bright an object looks from Earth. Smaller numbers mean brighter objects, and very bright objects can have negative magnitudes. A difference of five magnitudes corresponds to a brightness factor of 100. The V magnitudes in the constellation profiles refer to a visual photometric band; they are catalogue values rather than live observations. Under a dark, clear sky, a typical naked-eye limit for stars is about magnitude 6. Stars with higher numerical magnitudes are fainter and generally require binoculars or a telescope, although some observers can see fainter stars in exceptionally good conditions. Light pollution can lower this limiting magnitude significantly, for example to magnitude 3 or 4, so fewer stars are visible. The star itself has not become fainter: the brighter sky background makes it harder to see.
Sources: Swinburne University: limiting magnitude; AAVSO: observing conditions and limiting magnitudes
Other names and search terms: Bird of paradise, Aps
Apus is one of the 88 IAU-recognised constellations. Its common English description is: bird of paradise.
| Common English name | Bird of paradise |
|---|---|
| IAU abbreviation | Aps |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Paradys (Alpha Apodis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Paradys |
| Latin / catalogue designation | Alpha Apodis |
| Apparent magnitude (V) | 3.80 |
| Spectral type | K3IIICN0.5 |
| Distance from Earth | About 500ly |
| RA (ICRS / J2000) | 14h47m52s |
| Declination (ICRS / J2000) | -79d02m41s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Apodis; IAU: newly adopted star names
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 50,000ly |
| RA (J2000; approximate centre) | 16h25m48s |
| Declination (J2000; approximate centre) | -72d12m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Water bearer, Aqr
Aquarius is one of the 88 IAU-recognised constellations. Its common English description is: water bearer.
| Common English name | Water bearer |
|---|---|
| IAU abbreviation | Aqr |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Sadalsuud (Beta Aquarii) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Sadalsuud |
| Latin / catalogue designation | Beta Aquarii |
| Apparent magnitude (V) | 2.89 |
| Spectral type | G0Ib |
| Distance from Earth | About 550ly |
| RA (ICRS / J2000) | 21h31m34s |
| Declination (ICRS / J2000) | -05d34m16s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 34 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Sadalsuud
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 37,000ly |
| RA (J2000; approximate centre) | 21h33m30s |
| Declination (J2000; approximate centre) | -00d49m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 38 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: NASA: Messier 2; NGC 2000.0 position catalogue
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 650ly |
| RA (J2000; approximate centre) | 22h29m36s |
| Declination (J2000; approximate centre) | -20d48m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 18 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 1,400ly |
| RA (J2000; approximate centre) | 21h04m12s |
| Declination (J2000; approximate centre) | -11d22m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 28 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Eagle, Aql
Aquila is one of the 88 IAU-recognised constellations. Its common English description is: eagle.
| Common English name | Eagle |
|---|---|
| IAU abbreviation | Aql |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Altair (Alpha Aquilae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Altair |
| Latin / catalogue designation | Alpha Aquilae |
| Apparent magnitude (V) | 0.76 |
| Spectral type | A7Vn |
| Distance from Earth | About 17ly |
| RA (ICRS / J2000) | 19h50m47s |
| Declination (ICRS / J2000) | +08d52m06s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 48 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Altair
| Object type | Planetary nebula |
|---|---|
| Distance from Earth | About 6,500ly |
| RA (J2000; approximate centre) | 19h05m56s |
| Declination (J2000; approximate centre) | -05d59m32s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 33 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 6751; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Altar, Ara
Ara is one of the 88 IAU-recognised constellations. Its common English description is: altar.
| Common English name | Altar |
|---|---|
| IAU abbreviation | Ara |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Beta Arae |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Beta Arae |
| Apparent magnitude (V) | 2.85 |
| Spectral type | K0/1Ib |
| Distance from Earth | About 720ly |
| RA (ICRS / J2000) | 17h25m18s |
| Declination (ICRS / J2000) | -55d31m48s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Beta Arae
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 20,000ly |
| RA (J2000; approximate centre) | 17h25m30s |
| Declination (J2000; approximate centre) | -48d25m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 3,700ly |
| RA (J2000; approximate centre) | 16h41m18s |
| Declination (J2000; approximate centre) | -48d46m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Minute of arc
A unit of angle equal to 1/60 of a degree. The full Moon is approximately 30 arcminutes across. Angular minutes are not minutes of time.
Other names and search terms: Second of arc
A unit of angle equal to 1/60 of an arcminute, or 1/3,600 of a degree. It is used for small angular separations and measures of resolution.
Other names and search terms: Arecibo
A celebrated Puerto Rican radio and radar astronomy site, historically dominated by its enormous fixed reflector. The 305m telescope collapsed in December 2020 and is no longer an operating instrument.
| Location | Near Arecibo, Puerto Rico, USA |
|---|---|
| Type of site | Historic radio observatory site |
| Main instruments or facilities | Historic 305m fixed spherical radio reflector with suspended receiving equipment |
| Observing wavelengths | Radio and planetary radar during telescope operations |
| Scientific or historical importance | Important pulsar and planetary research, including the first confirmed exoplanets around a pulsar |
Sources: US National Science Foundation: Arecibo history and collapse
Other names and search terms: Ram, Ari
Aries is one of the 88 IAU-recognised constellations. Its common English description is: ram.
| Common English name | Ram |
|---|---|
| IAU abbreviation | Ari |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Hamal (Alpha Arietis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Hamal |
| Latin / catalogue designation | Alpha Arietis |
| Apparent magnitude (V) | 2.01 |
| Spectral type | K2-IIIbCa-1 |
| Distance from Earth | About 66ly |
| RA (ICRS / J2000) | 02h07m10s |
| Declination (ICRS / J2000) | +23d27m45s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 63 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Hamal
| Object type | Galaxy |
|---|---|
| Distance from Earth | About 120 million ly (redshift-based luminosity distance) |
| RA (J2000; approximate centre) | 01h59m20s |
| Declination (J2000; approximate centre) | +19d00m27s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 58 degrees. |
An indicative distance calculated from SIMBAD redshift z=0.008327, using H0=70km/s/Mpc and a flat cosmology with matter density parameter 0.3. This is a luminosity distance, not a direct measurement; local galaxy motions can cause substantial uncertainty, especially at low redshift.
Sources: SIMBAD: NGC 772
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: AOP, Armagh Observatory, Armagh Planetarium
An astronomical research and public education organisation combining Armagh's historic observatory with a planetarium and educational facilities.
| Location | Armagh, Northern Ireland, United Kingdom |
|---|---|
| Type of site | Research observatory, planetarium and public education site |
| Main instruments or facilities | Research programmes, historic telescopes and planetarium facilities |
| Observing wavelengths | Research across astronomy; public visualisation of the sky |
| Scientific or historical importance | Research into stars, the Solar System and galaxies, alongside a long history of astronomical education |
Other names and search terms: Satellite, Man-made satellite
A human-made object placed in orbit around Earth or another celestial body. Satellites may observe Earth, relay communications, provide navigation, carry people or conduct astronomy. A natural satellite, such as the Moon, formed naturally. A satellite constellation is an organised fleet of spacecraft, rather than a pattern of stars.
Sources: Official or institutional reference: Artificial satellite
Other names and search terms: Plough, Big Dipper, Summer Triangle
A recognisable pattern of stars that is not itself one of the 88 officially defined constellation regions. An asterism may lie within one constellation, such as the Plough (Big Dipper) in Ursa Major, or span several constellations, such as the Summer Triangle. Its stars need not be physically close together: they form a pattern from our viewpoint on Earth. A constellation, by contrast, is an officially bounded area of sky.
Other names and search terms: Asteroids
A relatively small body orbiting the Sun, usually made mainly of rock, metal or carbon-rich material. Most are found in the main asteroid belt between Mars and Jupiter, but many follow other orbits. Most are irregularly shaped. Asteroids generally lack the conspicuous gas-and-dust activity of comets, although some show activity and the distinction is not absolute.
Precise measurement of celestial positions and how they change over time. Stellar parallax and proper motion are important astrometric measurements. Hipparcos and Gaia made major space-based astrometric catalogues.
Sources: ESA: Gaia astrometry
Other names and search terms: Cosmonaut
A person trained for travel and work in space. Cosmonaut is the equivalent term used in the Russian space programme. Training or selection does not itself mean that someone has flown in space; individual biographies distinguish these milestones.
Other names and search terms: Astronauts directory
Selected pioneers of human spaceflight, with an emphasis on British astronauts and British-born NASA astronauts. Biographies distinguish nationality, programme affiliation, training and completed flights.
| Astronaut | Background / achievements |
|---|---|
| Helen Sharman | The first British person in space. |
| Tim Peake | A British ESA astronaut from Chichester, West Sussex, who travelled to the ISS in December 2015 for the Principia mission. |
| Michael Foale | A British-American NASA astronaut born in Louth, Lincolnshire. |
| Piers Sellers | A British-born NASA astronaut and climate scientist from Crowborough, East Sussex. |
| Rosemary Coogan | A British ESA astronaut and astrophysicist from Belfast, Northern Ireland. |
| Yuri Gagarin | The first human to travel into space and orbit Earth. |
| Valentina Tereshkova | The first woman in space. |
| Neil Armstrong | Commander of Apollo 11 and the first person to step onto the Moon, in July 1969. |
| Buzz Aldrin | Apollo 11 lunar module pilot and the second person to walk on the Moon, in July 1969. |
| Sally Ride | The first American woman in space, flying aboard Space Shuttle Challenger on STS-7 in June 1983. |
A royal appointment created in 1675, originally associated with the Royal Observatory Greenwich and improving navigation through accurate astronomical observations. Today it is an honorary role advising the monarch on astronomical matters and promoting astronomy. As checked on 25 October 2026, the holder is Professor Michele Dougherty, appointed in July 2025 as the first woman in the role, succeeding Lord Martin Rees. The Astronomer Royal for Scotland is a separate appointment.
Sources: Official reference: Astronomer Royal
Other names and search terms: Astronomers through history directory
Selected observers, theorists and communicators who helped change our understanding of the sky. This is an introduction, not a complete history: astronomy developed through many cultures and the work of numerous observers, instrument makers and collaborators.
| Astronomer | Contributions to astronomy |
|---|---|
| Hipparchus | An ancient Greek astronomer remembered for careful stellar measurements and discovering the precession of the equinoxes by comparing observations from different eras. |
| Claudius Ptolemy | An astronomer working in Alexandria whose Almagest assembled a major star catalogue and a mathematical Earth-centred model of planetary motion. |
| Nicolaus Copernicus | A Polish astronomer whose 1543 book set out a mathematical Sun-centred model in which Earth rotates and orbits the Sun. |
| Tycho Brahe | A Danish astronomer who obtained exceptionally precise naked-eye measurements of stars and planets before telescopic astronomy. |
| Johannes Kepler | A German astronomer who used Tycho Brahe's observations to formulate three laws of planetary motion. |
| Galileo Galilei | An Italian astronomer who used improved telescopes to investigate the sky from 1609. |
| Sir Isaac Newton | An English mathematician and physicist whose laws of motion and universal gravitation explained planetary orbits. |
| Edmond Halley | An English astronomer who recognised that several recorded comet appearances represented the same returning object and predicted its next return. |
| John Flamsteed | The first Astronomer Royal, appointed in 1675, who established systematic observations at Greenwich. |
| Sir William Herschel | A German-born British astronomer and telescope maker who discovered Uranus in 1781 and infrared radiation in 1800. |
| Caroline Herschel | A German-born British astronomer who discovered comets and helped produce extensive deep-sky catalogues. |
| Charles Messier | A French comet hunter whose catalogue recorded fuzzy-looking objects that could be mistaken for comets. |
| Henrietta Swan Leavitt | An American astronomer who discovered the relationship between the pulsation periods and luminosities of Cepheid variable stars. |
| Cecilia Payne-Gaposchkin | A British-born American astronomer whose 1925 research showed that stars consist predominantly of hydrogen and helium. |
| Edwin Hubble | An American astronomer who used Cepheid variables to establish that the Andromeda system lies beyond the Milky Way. |
| Albert Einstein | A theoretical physicist whose general theory of relativity describes gravity through the curvature of spacetime. |
| Sir Bernard Lovell | A British radio astronomer who founded Jodrell Bank Observatory and led development of its giant steerable radio telescope. |
| Sir Martin Ryle | A British radio astronomer who pioneered aperture-synthesis techniques, combining observations from separated antennas to make detailed radio images. |
| Dame Jocelyn Bell Burnell | A Northern Irish astrophysicist who identified the first pulsar signals in 1967 while a Cambridge research student working with Antony Hewish. |
| Sir Patrick Moore | A British amateur astronomer, author and broadcaster who inspired generations of observers through BBC television's The Sky at Night, which he began presenting in 1957. |
| Professor Michele Dougherty | A space physicist and planetary scientist appointed Astronomer Royal in July 2025, the first woman to hold the role. |
| Professor Chris Lintott | A British astrophysicist, author and broadcaster at the University of Oxford, well known as a presenter of BBC television's The Sky at Night. |
Other names and search terms: AU
A unit of distance, abbreviated AU, defined as exactly 149,597,870.7km. It is approximately the semi-major axis of Earth's orbit and is convenient for comparing distances within the Solar System.
Other names and search terms: Astronomical organisations, Astronomy authorities, Authorities, Astronomy societies, Organisations
A guide to organisations encountered in astronomy, with an emphasis on the UK. Their roles differ: space agencies run programmes, learned societies support science, amateur associations support observing, and local societies and science centres provide community learning. The links below explain each organisation and lead to its official information.
| Organisation | Role and location / area served |
|---|---|
| NASA | Government space and aeronautics organisation; United States; international scientific collaborations |
| Royal Astronomical Society | Learned society for astronomy and geophysics; Burlington House, London, England; UK and international membership |
| British Astronomical Association | Amateur astronomy association; UK-based, with an international membership |
| Southern Area Group of Astronomical Societies | Regional network of astronomical societies; Southern England |
| Observatory Science Centre and Museum | Public science centre, museum and historic observatory site; Herstmonceux, East Sussex, England |
| UK Space Agency | Government space organisation; United Kingdom |
| Society for Popular Astronomy | Amateur astronomy society with a strong beginner focus; United Kingdom |
| Federation of Astronomical Societies | Federation of astronomy societies; United Kingdom |
| Science and Technology Facilities Council | Research council and provider of scientific facilities; United Kingdom; research facilities and partnerships in the UK and overseas |
| European Space Agency | Intergovernmental space agency; Europe; headquarters in Paris, France |
| International Astronomical Union | Professional scientific union and coordinating body; International |
| European Southern Observatory | Intergovernmental ground-based astronomy organisation; European organisation; major observatory sites in Chile |
| Lewes Astronomical Society | Local astronomical society; Lewes and surrounding communities, East Sussex, England |
Taking photographs of astronomical objects, from the Moon and planets to star clusters, nebulae and galaxies.
Other names and search terms: ALMA
An international array of antennas that combines signals to investigate cold gas, dust, forming stars and planets, and distant galaxies. It is a radio interferometer rather than a single enormous filled dish.
| Location | Chajnantor Plateau, Atacama region, Chile; main array approximately 5,000m above sea level |
|---|---|
| Type of site | Millimetre/submillimetre interferometer |
| Main instruments or facilities | 66 antennas: 54 of 12m diameter and 12 of 7m diameter |
| Observing wavelengths | Millimetre and submillimetre radio wavelengths |
| Scientific or historical importance | Detailed observations of planet-forming discs and cold material that optical telescopes may not reveal |
Sources: ALMA: factsheet; ESO: ALMA location and partnership
Other names and search terms: Charioteer, Aur
Auriga is one of the 88 IAU-recognised constellations. Its common English description is: charioteer.
| Common English name | Charioteer |
|---|---|
| IAU abbreviation | Aur |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Capella (Alpha Aurigae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Capella |
| Latin / catalogue designation | Alpha Aurigae |
| Apparent magnitude (V) | 0.08 |
| Spectral type | G3III: |
| Distance from Earth | About 43ly |
| RA (ICRS / J2000) | 05h16m41s |
| Declination (ICRS / J2000) | +45d59m53s |
| Among the ten brightest night-sky stars? | Yes: reference rank 6 (Sun excluded). |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 85 degrees. |
Distance is a rounded estimate from the catalogue parallax. Capella is a multiple system; the spectral type shown is the catalogue combined classification.
Sources: SIMBAD: Capella; ESA Hipparcos brightness reference
| Object type | Open star cluster |
|---|---|
| Distance from Earth | About 4,700ly |
| RA (J2000; approximate centre) | 05h52m18s |
| Declination (J2000; approximate centre) | +32d32m42s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 72 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 2099; Cantat-Gaudin et al. (2020), cluster distances
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
An object's horizontal direction, normally measured from north through east: north is 0 degrees, east 90, south 180 and west 270.
Other names and search terms: Barlow
An accessory that increases a telescope's effective focal length and therefore its magnification with a given eyepiece. A 2x Barlow approximately doubles the power; with conventional Barlows the factor can change with spacing.
Other names and search terms: Eyepiece barrel, 1.25 inch, 2 inch
The outside diameter of the part of an eyepiece that fits into the holder. Common sizes are 1.25 inches and 2 inches. This determines mechanical compatibility, not magnification.
Other names and search terms: Binary stars, Physical binary, Binaries
Two stars bound by gravity and orbiting their common centre of mass. Some can be separated visually through a telescope; others are detected through changes in their spectra, brightness or positions. A binary can also be part of a larger multiple system.
Sources: NASA: double-star systems; NAOC: spectroscopic and eclipsing binaries
Other names and search terms: Herdsman, Boo
Bootes is one of the 88 IAU-recognised constellations. Its common English description is: herdsman.
| Common English name | Herdsman |
|---|---|
| IAU abbreviation | Boo |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Arcturus (Alpha Bootis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Arcturus |
| Latin / catalogue designation | Alpha Bootis |
| Apparent magnitude (V) | -0.05 |
| Spectral type | K1.5IIIFe-0.5 |
| Distance from Earth | About 37ly |
| RA (ICRS / J2000) | 14h15m40s |
| Declination (ICRS / J2000) | +19d10m57s |
| Among the ten brightest night-sky stars? | Yes: reference rank 4 (Sun excluded). |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 58 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Arcturus; ESA Hipparcos brightness reference
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Izar |
| Latin / catalogue designation | Epsilon Bootis |
| System or component described | Bright primary; the quoted catalogue spectrum describes this component |
| Apparent magnitude (V) | 2.45 |
| Spectral type | K0-II-III |
| Distance from Earth | About 236ly |
| RA (ICRS / J2000) | 14h44m59s |
| Declination (ICRS / J2000) | +27d04m27s |
| System structure | A physical binary with a bright evolved star and a fainter hot companion. |
| Observing interest | A celebrated colour-contrast pair, but its close separation and unequal brightness make it more demanding than a wide double. |
| Visibility from Lewes | Visible at a suitable season and time; maximum altitude about 66 degrees. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate.
Sources: SIMBAD: Izar
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 59 million ly |
| RA (J2000; approximate centre) | 13h37m30s |
| Declination (J2000; approximate centre) | +08d53m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 48 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Ten brightest stars, Top ten stars, 10 brightest stars
A reference ordering of the ten brightest night-sky stars or unresolved stellar systems, as seen from Earth, excluding the Sun. It follows the ESA Hipparcos list. Several stars vary in brightness, so their order can change. Follow a star's link to its constellation profile for its magnitude, spectral type, distance and coordinates.
| Brightness rank / star | Constellation | Visibility from Lewes |
|---|---|---|
| 1. Sirius | Canis Major | Can be seen at a suitable season and time; maximum altitude about 22 degrees |
| 2. Canopus | Carina | Never visible from Lewes |
| 3. Alpha Centauri A+B | Centaurus | Never visible from Lewes |
| 4. Arcturus | Bootes | Can be seen at a suitable season and time; maximum altitude about 58 degrees |
| 5. Vega | Lyra | Can be seen at a suitable season and time; maximum altitude about 78 degrees |
| 6. Capella | Auriga | Can be seen at a suitable season and time; maximum altitude about 85 degrees |
| 7. Rigel | Orion | Can be seen at a suitable season and time; maximum altitude about 31 degrees |
| 8. Procyon | Canis Minor | Can be seen at a suitable season and time; maximum altitude about 44 degrees |
| 9. Achernar | Eridanus | Never visible from Lewes |
| 10. Betelgeuse | Orion | Can be seen at a suitable season and time; maximum altitude about 47 degrees |
Sources: ESA Hipparcos: brightest stars
Other names and search terms: BAA
A UK-based organisation supporting amateur observational astronomy since 1890. Its specialist observing sections help people develop their skills and contribute scientifically useful observations, often in collaboration with professional astronomers.
| Area or location | UK-based, with an international membership |
|---|---|
| Role | Amateur astronomy association |
| Useful for | Observing advice, specialist sections, observations, meetings and publications |
Sources: Official organisation information
Other names and search terms: Edwin Aldrin
Apollo 11 lunar module pilot and the second person to walk on the Moon, in July 1969. He had previously demonstrated important spacewalking techniques on Gemini 12. The lunar landing was a shared achievement of the crew and a much larger engineering and scientific team.
| Dates | Born 1930; Apollo 11 in 1969 |
|---|---|
| Background | American; NASA |
Other names and search terms: Chisel, Cae
Caelum is one of the 88 IAU-recognised constellations. Its common English description is: chisel.
| Common English name | Chisel |
|---|---|
| IAU abbreviation | Cae |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Alpha Caeli |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Caeli |
| Apparent magnitude (V) | 4.45 |
| Spectral type | F2V |
| Distance from Earth | About 66ly |
| RA (ICRS / J2000) | 04h40m34s |
| Declination (ICRS / J2000) | -41d51m50s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Caeli
| Object type | Galaxy |
|---|---|
| Distance from Earth | About 49 million ly (redshift-based luminosity distance) |
| RA (J2000; approximate centre) | 04h49m56s |
| Declination (J2000; approximate centre) | -31d57m56s |
| Visibility from Lewes | Rises, but very low: maximum altitude about 7 degrees; needs a clear southern horizon. |
An indicative distance calculated from SIMBAD redshift z=0.003513, using H0=70km/s/Mpc and a flat cosmology with matter density parameter 0.3. This is a luminosity distance, not a direct measurement; local galaxy motions can cause substantial uncertainty, especially at low redshift.
Sources: SIMBAD: NGC 1679
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Caldwell, Caldwell catalog
Patrick Moore's selection of 109 deep-sky observing targets, identified by C numbers. It complements the Messier catalogue and includes many southern-sky objects that cannot be seen from Lewes. C is the Caldwell observing-list number; NGC and IC are identifiers from other catalogues.
Sources: NASA: Hubble Caldwell catalogue
The outermost Galilean moon of Jupiter. Its ancient, heavily cratered surface preserves a long history of impacts. Spacecraft measurements suggest that it may also contain a salty ocean beneath its surface.
| Parent planet | Jupiter |
|---|---|
| Order among the Galilean moons | 4 from Jupiter |
| Mean diameter | About 4,821km |
| Orbital distance (semi-major axis) | 1,882,700km from the planet's centre |
| Orbital period | 16.68902 Earth days |
| Rotation period | 16.68902 Earth days; synchronous with its orbit |
| Composition | Rock and water ice |
Values are approximate reference figures. Orbital distance is measured from the centre of the parent planet, not its cloud tops. The rotation period is relative to distant stars, not the interval between sunrises. These moving Solar System objects have no single fixed RA/Dec position or distance from Earth.
Sources: NASA: Callisto facts; NASA satellite fact sheet (orbital parameters); JPL: satellite physical parameters (mean radii)
Other names and search terms: Giraffe, Cam
Camelopardalis is one of the 88 IAU-recognised constellations. Its common English description is: giraffe.
| Common English name | Giraffe |
|---|---|
| IAU abbreviation | Cam |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Beta Camelopardalis |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Beta Camelopardalis |
| Apparent magnitude (V) | 4.02 |
| Spectral type | G1Ib |
| Distance from Earth | About 840ly |
| RA (ICRS / J2000) | 05h03m25s |
| Declination (ICRS / J2000) | +60d26m32s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 80 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Beta Camelopardalis
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 11 million ly |
| RA (J2000; approximate centre) | 03h46m48s |
| Declination (J2000; approximate centre) | +68d06m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 73 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 12 million ly |
| RA (J2000; approximate centre) | 07h36m54s |
| Declination (J2000; approximate centre) | +65d36m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 75 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Crab, Cnc
Cancer is one of the 88 IAU-recognised constellations. Its common English description is: crab.
| Common English name | Crab |
|---|---|
| IAU abbreviation | Cnc |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Tarf (Beta Cancri) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Tarf |
| Latin / catalogue designation | Beta Cancri |
| Apparent magnitude (V) | 3.52 |
| Spectral type | K4IIIBa0.5: |
| Distance from Earth | About 320ly |
| RA (ICRS / J2000) | 08h16m31s |
| Declination (ICRS / J2000) | +09d11m08s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 48 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Tarf
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 600ly |
| RA (J2000; approximate centre) | 08h40m06s |
| Declination (J2000; approximate centre) | +19d59m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 59 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Open Cluster |
|---|---|
| Distance from Earth | ~2,800ly |
| RA (J2000; approximate centre) | 08h50m24s |
| Declination (J2000; approximate centre) | +11d49m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 51 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Hunting dogs, CVn
Canes Venatici is one of the 88 IAU-recognised constellations. Its common English description is: hunting dogs.
| Common English name | Hunting dogs |
|---|---|
| IAU abbreviation | CVn |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Cor Caroli (Alpha2 Canum Venaticorum) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Cor Caroli |
| Latin / catalogue designation | Alpha2 Canum Venaticorum |
| Apparent magnitude (V) | 2.88 |
| Spectral type | A0VpSiEu |
| Distance from Earth | About 100ly |
| RA (ICRS / J2000) | 12h56m02s |
| Declination (ICRS / J2000) | +38d19m06s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 77 degrees. |
| System structure | The brighter Alpha2 component of the Cor Caroli visual pair. |
| Observing interest | A pleasing wide double with a fainter Alpha1 companion, usually straightforward in a small telescope. |
Distance is a rounded estimate from the catalogue parallax. Data describe the brighter Alpha2 component of the Cor Caroli pair.
Sources: SIMBAD: Cor Caroli
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Cor Caroli companion |
| Latin / catalogue designation | Alpha1 Canum Venaticorum |
| System or component described | Fainter visual component |
| Apparent magnitude (V) | 5.60 |
| Spectral type | F2V |
| Distance from Earth | About 107ly |
| RA (ICRS / J2000) | 12h56m00s |
| Declination (ICRS / J2000) | +38d18m53s |
| System structure | The fainter visual companion to Cor Caroli's brighter Alpha2 component. |
| Observing interest | A widely separated white pair, attractive in a small telescope. |
| Visibility from Lewes | Visible at a suitable season and time; maximum altitude about 77 degrees. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate. Separate astrometric solutions for multiple stars can give somewhat different distance estimates; the listed value is this component's rounded catalogue parallax distance.
Sources: SIMBAD: Cor Caroli companion
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 31 million ly |
| RA (J2000; approximate centre) | 13h29m54s |
| Declination (J2000; approximate centre) | +47d12m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 86 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 34,000ly |
| RA (J2000; approximate centre) | 13h42m12s |
| Declination (J2000; approximate centre) | +28d23m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 68 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: NASA: Messier 3; NGC 2000.0 position catalogue
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 27 million ly |
| RA (J2000; approximate centre) | 13h15m48s |
| Declination (J2000; approximate centre) | +42d02m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 81 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Greater dog, CMa
Canis Major is one of the 88 IAU-recognised constellations. Its common English description is: greater dog.
| Common English name | Greater dog |
|---|---|
| IAU abbreviation | CMa |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Sirius (Alpha Canis Majoris) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Sirius |
| Latin / catalogue designation | Alpha Canis Majoris |
| Apparent magnitude (V) | -1.46 |
| Spectral type | A0mA1Va |
| Distance from Earth | About 8.6ly |
| RA (ICRS / J2000) | 06h45m09s |
| Declination (ICRS / J2000) | -16d42m58s |
| Among the ten brightest night-sky stars? | Yes: reference rank 1 (Sun excluded). |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 22 degrees. |
| System structure | A bright main-sequence star with a white-dwarf companion. |
| Observing interest | The bright star is easy to see; separating the faint companion from its glare is a demanding telescope observation. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Sirius; ESA Hipparcos brightness reference; NASA: Sirius binary
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Sirius B |
| Latin / catalogue designation | Alpha Canis Majoris B |
| System or component described | Individual white dwarf |
| Apparent magnitude (V) | 8.44 |
| Spectral type | DA1.9 |
| Distance from Earth | About 8.6ly (adopted system distance) |
| RA (ICRS / J2000) | 06h45m09s |
| Declination (ICRS / J2000) | -16d43m01s |
| System structure | The white-dwarf companion in the Sirius binary; the pair orbit in about 50 years. |
| Observing interest | A challenging observation: the faint companion is overwhelmed by the much brighter primary's glare. Good seeing, suitable equipment and favourable separation are important. |
| Visibility from Lewes | Visible at a suitable season and time; maximum altitude about 22 degrees. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate. The adopted distance follows the Sirius system reference, rather than treating the companion's catalogue parallax as an independent distance to an unrelated star.
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 3,700ly |
| RA (J2000; approximate centre) | 07h17m48s |
| Declination (J2000; approximate centre) | -15d37m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 24 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Lesser dog, CMi
Canis Minor is one of the 88 IAU-recognised constellations. Its common English description is: lesser dog.
| Common English name | Lesser dog |
|---|---|
| IAU abbreviation | CMi |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Procyon (Alpha Canis Minoris) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Procyon |
| Latin / catalogue designation | Alpha Canis Minoris |
| Apparent magnitude (V) | 0.37 |
| Spectral type | F5IV-V+DQZ |
| Distance from Earth | About 11ly |
| RA (ICRS / J2000) | 07h39m18s |
| Declination (ICRS / J2000) | +05d13m30s |
| Among the ten brightest night-sky stars? | Yes: reference rank 8 (Sun excluded). |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 44 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Procyon; ESA Hipparcos brightness reference
| Object type | Galaxy |
|---|---|
| Distance from Earth | About 220 million ly (redshift-based luminosity distance) |
| RA (J2000; approximate centre) | 07h56m49s |
| Declination (J2000; approximate centre) | +07d28m41s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 47 degrees. |
An indicative distance calculated from SIMBAD redshift z=0.015592, using H0=70km/s/Mpc and a flat cosmology with matter density parameter 0.3. This is a luminosity distance, not a direct measurement; local galaxy motions can cause substantial uncertainty, especially at low redshift.
Sources: SIMBAD: NGC 2485
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Sea goat, Cap
Capricornus is one of the 88 IAU-recognised constellations. Its common English description is: sea goat.
| Common English name | Sea goat |
|---|---|
| IAU abbreviation | Cap |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Deneb Algedi (Delta Capricorni) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Deneb Algedi |
| Latin / catalogue designation | Delta Capricorni |
| Apparent magnitude (V) | 2.83 |
| Spectral type | kA5hF0mF2III |
| Distance from Earth | About 39ly |
| RA (ICRS / J2000) | 21h47m02s |
| Declination (ICRS / J2000) | -16d07m38s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 23 degrees. |
Distance is a rounded estimate from the catalogue parallax. The quoted V magnitude is a representative catalogue value, not a live measurement.
Sources: SIMBAD: Deneb Algedi
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 28,000ly |
| RA (J2000; approximate centre) | 21h40m24s |
| Declination (J2000; approximate centre) | -23d11m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 16 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Keel, Car
Carina is one of the 88 IAU-recognised constellations. Its common English description is: keel.
| Common English name | Keel |
|---|---|
| IAU abbreviation | Car |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Canopus (Alpha Carinae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Canopus |
| Latin / catalogue designation | Alpha Carinae |
| Apparent magnitude (V) | -0.74 |
| Spectral type | A9II |
| Distance from Earth | About 310ly |
| RA (ICRS / J2000) | 06h23m57s |
| Declination (ICRS / J2000) | -52d41m44s |
| Among the ten brightest night-sky stars? | Yes: reference rank 2 (Sun excluded). |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Canopus; ESA Hipparcos brightness reference
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 6,000ly |
| RA (J2000; approximate centre) | 09h21m24s |
| Declination (J2000; approximate centre) | -58d19m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Emission Nebula |
|---|---|
| Distance from Earth | 7,500ly |
| RA (J2000; approximate centre) | 10h43m48s |
| Declination (J2000; approximate centre) | -59d52m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
A German-born British astronomer who discovered comets and helped produce extensive deep-sky catalogues. She worked closely with her brother William, recording and reducing observations, while making important discoveries of her own. She received a royal salary for astronomical work from 1787.
| Dates | 1750-1848 |
|---|---|
| Background | German-born British astronomer |
Sources: Official or institutional reference: Caroline Herschel
Other names and search terms: Cassini, Huygens
A joint mission comprising NASA's Cassini Saturn orbiter and ESA's Huygens Titan lander, with Italian Space Agency participation. Cassini investigated Saturn, its rings and moons from 2004 to 2017. Huygens landed on Titan in January 2005. Cassini revealed active icy plumes at Enceladus and ended with a planned plunge into Saturn to protect potentially habitable moons.
| Programme / agency | NASA / ESA / ASI |
|---|---|
| Key dates | Launched 1997; Saturn arrival 2004; mission ended 2017 |
| Destination / science location | Saturn system |
Sources: Official or institutional reference: Cassini-Huygens
Other names and search terms: Queen, Cas
Cassiopeia is one of the 88 IAU-recognised constellations. Its common English description is: queen.
| Common English name | Queen |
|---|---|
| IAU abbreviation | Cas |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Schedar (Alpha Cassiopeiae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Schedar |
| Latin / catalogue designation | Alpha Cassiopeiae |
| Apparent magnitude (V) | 2.23 |
| Spectral type | K0-IIIa |
| Distance from Earth | About 230ly |
| RA (ICRS / J2000) | 00h40m30s |
| Declination (ICRS / J2000) | +56d32m14s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 84 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Schedar
| Role | Variable star that can outshine Schedar |
|---|---|
| Common / proper name | Tiansi |
| Latin / catalogue designation | Gamma Cassiopeiae |
| Apparent magnitude (V) | 2.39 |
| Spectral type | B0.5IVpe |
| Distance from Earth | About 550ly |
| RA (ICRS / J2000) | 00h56m43s |
| Declination (ICRS / J2000) | +60d43m00s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 80 degrees. |
Distance is a rounded estimate from the catalogue parallax. The quoted V magnitude is a representative catalogue value, not a live measurement.
Sources: SIMBAD: Gamma Cassiopeiae; IAU: newly adopted star names
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Achird |
| Latin / catalogue designation | Eta Cassiopeiae |
| System or component described | Brighter component of the Achird binary |
| Apparent magnitude (V) | 3.44 |
| Spectral type | F9V |
| Distance from Earth | About 19.3ly |
| RA (ICRS / J2000) | 00h49m06s |
| Declination (ICRS / J2000) | +57d48m55s |
| System structure | A physical binary with a brighter Sun-like star and a cooler, fainter companion. |
| Observing interest | An attractive contrasting pair for a small telescope. |
| Visibility from Lewes | Circumpolar from Lewes: remains above the horizon throughout the day and night; needs a dark, clear sky to observe. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate. The catalogue magnitude and spectrum shown describe the brighter component; the companion is not included in those single-star values.
Sources: SIMBAD: Achird
| Object type | Emission Nebula |
|---|---|
| Distance from Earth | 7,000ly |
| RA (J2000; approximate centre) | 23h20m42s |
| Declination (J2000; approximate centre) | +61d12m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 80 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Dwarf Galaxy |
|---|---|
| Distance from Earth | 2.5 million ly |
| RA (J2000; approximate centre) | 00h33m12s |
| Declination (J2000; approximate centre) | +48d30m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 88 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye. Schedar is the usual reference choice, but variable Gamma Cassiopeiae can become brighter.
Sources: IAU: the 88 constellations
An optical design combining refracting elements, such as corrector lenses, with mirrors. Common examples include Schmidt-Cassegrain and Maksutov-Cassegrain telescopes, which provide a long effective focal length in a compact tube.
Other names and search terms: Cecilia Payne, Payne-Gaposchkin
A British-born American astronomer whose 1925 research showed that stars consist predominantly of hydrogen and helium. She used stellar spectra and atomic physics to connect observed absorption lines with physical conditions, transforming understanding of stellar composition.
| Dates | 1900-1979 |
|---|---|
| Background | Born in Wendover, England; worked at Harvard |
Sources: Official or institutional reference: Cecilia Payne-Gaposchkin
The imaginary circle on the sky directly above Earth's equator. It is the reference for measuring declination.
Other names and search terms: North celestial pole, South celestial pole
One of the two directions on the sky towards which Earth's rotation axis points. Polaris is close to the north celestial pole, but not exactly on it.
Other names and search terms: Centaur, Cen
Centaurus is one of the 88 IAU-recognised constellations. Its common English description is: centaur.
| Common English name | Centaur |
|---|---|
| IAU abbreviation | Cen |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Alpha Centauri A+B |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Alpha Centauri A+B |
| Latin / catalogue designation | Alpha Centauri |
| Apparent magnitude (V) | -0.28 |
| Spectral type | G2V+K1V |
| Distance from Earth | About 4.3ly |
| RA (ICRS / J2000) | 14h39m37s |
| Declination (ICRS / J2000) | -60d50m02s |
| Among the ten brightest night-sky stars? | Yes: reference rank 3 (Sun excluded). |
| Visibility from Lewes | Never visible from Lewes. |
| System structure | A bright binary accompanied at much greater distance by the red dwarf Proxima Centauri, forming a triple. |
| Observing interest | The bright pair is an important southern double, but none of this system rises from Lewes. |
Distance is a rounded estimate from the catalogue parallax. Magnitude and spectral type refer to the unresolved multiple system.
Sources: SIMBAD: Alpha Centauri A+B; ESA Hipparcos brightness reference
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Proxima Centauri |
| Latin / catalogue designation | Alpha Centauri C |
| System or component described | Individual red-dwarf star |
| Apparent magnitude (V) | 11.13 |
| Spectral type | M5.5Ve |
| Distance from Earth | About 4.25ly |
| RA (ICRS / J2000) | 14h29m43s |
| Declination (ICRS / J2000) | -62d40m46s |
| System structure | The distant red-dwarf member of the Alpha Centauri triple. |
| Observing interest | The nearest star beyond the Sun, but too faint for unaided-eye viewing. It cannot be seen from Lewes. |
| Visibility from Lewes | Never visible from Lewes. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate.
Sources: SIMBAD: Proxima Centauri; NASA: Proxima in the Alpha Centauri triple
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 17,000ly |
| RA (J2000; approximate centre) | 13h26m48s |
| Declination (J2000; approximate centre) | -47d29m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Elliptical Galaxy |
|---|---|
| Distance from Earth | 11 million ly |
| RA (J2000; approximate centre) | 13h25m30s |
| Declination (J2000; approximate centre) | -43d01m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
A part of the optical system, usually a secondary mirror and its support, that blocks some incoming light. It reduces transmission and redistributes light in the diffraction pattern, affecting contrast.
Other names and search terms: King, Cep
Cepheus is one of the 88 IAU-recognised constellations. Its common English description is: king.
| Common English name | King |
|---|---|
| IAU abbreviation | Cep |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Alderamin (Alpha Cephei) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Alderamin |
| Latin / catalogue designation | Alpha Cephei |
| Apparent magnitude (V) | 2.46 |
| Spectral type | A8Vn |
| Distance from Earth | About 49ly |
| RA (ICRS / J2000) | 21h18m35s |
| Declination (ICRS / J2000) | +62d35m08s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 78 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alderamin
| Object type | Reflection Nebula |
|---|---|
| Distance from Earth | 1,400ly |
| RA (J2000; approximate centre) | 21h00m30s |
| Declination (J2000; approximate centre) | +68d10m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 73 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 3,500ly |
| RA (J2000; approximate centre) | 00h13m00s |
| Declination (J2000; approximate centre) | +72d32m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 68 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Sea monster (often called the whale), Cet
Cetus is one of the 88 IAU-recognised constellations. Its common English description is: sea monster (often called the whale).
| Common English name | Sea monster (often called the whale) |
|---|---|
| IAU abbreviation | Cet |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Diphda (Beta Ceti) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Diphda |
| Latin / catalogue designation | Beta Ceti |
| Apparent magnitude (V) | 2.01 |
| Spectral type | G9.5IIICH-1 |
| Distance from Earth | About 96ly |
| RA (ICRS / J2000) | 00h43m35s |
| Declination (ICRS / J2000) | -17d59m12s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 21 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Diphda
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 45 million ly |
| RA (J2000; approximate centre) | 02h42m42s |
| Declination (J2000; approximate centre) | -00d01m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 39 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 1,600ly |
| RA (J2000; approximate centre) | 00h47m00s |
| Declination (J2000; approximate centre) | -11d53m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 27 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Chameleon, Cha
Chamaeleon is one of the 88 IAU-recognised constellations. Its common English description is: chameleon.
| Common English name | Chameleon |
|---|---|
| IAU abbreviation | Cha |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Alpha Chamaeleontis |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Chamaeleontis |
| Apparent magnitude (V) | 4.05 |
| Spectral type | F5VFe-0.8 |
| Distance from Earth | About 64ly |
| RA (ICRS / J2000) | 08h18m32s |
| Declination (ICRS / J2000) | -76d55m11s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Chamaeleontis
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 5,500ly |
| RA (J2000; approximate centre) | 10h09m30s |
| Declination (J2000; approximate centre) | -80d52m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Chandra, CXO
A NASA space observatory designed for sharp X-ray imaging and spectroscopy of very hot and energetic regions of the Universe.
| Agency or partnership | NASA |
|---|---|
| Science orbit / location | Highly elliptical Earth orbit |
| Main telescope or instruments | Four nested pairs of grazing-incidence mirrors; outer mirror assembly about 1.2m across |
| Observing wavelengths | X-rays |
| Mission history | Launched in 1999 |
| Scientific importance | Detailed studies of supernova remnants, galaxy-cluster gas and regions around black holes |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Other names and search terms: Messier
A French comet hunter whose catalogue recorded fuzzy-looking objects that could be mistaken for comets. Many are now favourite observing targets, including galaxies, nebulae and star clusters. The modern Messier list has 110 entries and reflects contributions from observers including Pierre Mechain.
| Dates | 1730-1817 |
|---|---|
| Background | French astronomer |
Sources: Official or institutional reference: Charles Messier
Other names and search terms: Colour fringing
An optical effect in which different colours of light are not brought to the same focus, producing coloured fringes around bright objects. It is most noticeable in some simpler refracting telescopes.
Other names and search terms: Drawing compasses, Cir
Circinus is one of the 88 IAU-recognised constellations. Its common English description is: drawing compasses.
| Common English name | Drawing compasses |
|---|---|
| IAU abbreviation | Cir |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Xami (Alpha Circini) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Xami |
| Latin / catalogue designation | Alpha Circini |
| Apparent magnitude (V) | 3.19 |
| Spectral type | A7VpSrCrEu |
| Distance from Earth | About 53ly |
| RA (ICRS / J2000) | 14h42m30s |
| Declination (ICRS / J2000) | -64d58m30s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Circini; IAU: newly adopted star names
| Object type | Spiral galaxy with an active nucleus |
|---|---|
| Distance from Earth | About 13 million ly |
| RA (J2000; approximate centre) | 14h13m10s |
| Declination (J2000; approximate centre) | -65d20m20s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: Circinus Galaxy; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Circumpolar star
Describes an object that never sets below the horizon from a particular latitude. From Lewes, stars north of approximately +39.1 degrees declination are geometrically circumpolar. This does not mean they are visible in daylight or through cloud, and a low object may be hidden by buildings or terrain. Polaris is circumpolar from Lewes.
Sources: NASA: circumpolar constellations
Other names and search terms: Ptolemy
An astronomer working in Alexandria whose Almagest assembled a major star catalogue and a mathematical Earth-centred model of planetary motion. Although its physical model was later replaced, the work shaped astronomy for many centuries.
| Dates | Approximately 100-170 CE |
|---|---|
| Background | Alexandria, Roman Egypt |
Sources: Official or institutional reference: Claudius Ptolemy
Aligning the optical components of a telescope so that they work together correctly. Poor collimation can soften detail, especially at high power. Finder alignment is a separate adjustment.
Other names and search terms: Dove, Col
Columba is one of the 88 IAU-recognised constellations. Its common English description is: dove.
| Common English name | Dove |
|---|---|
| IAU abbreviation | Col |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Phact (Alpha Columbae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Phact |
| Latin / catalogue designation | Alpha Columbae |
| Apparent magnitude (V) | 2.65 |
| Spectral type | B9Ve |
| Distance from Earth | About 290ly |
| RA (ICRS / J2000) | 05h39m39s |
| Declination (ICRS / J2000) | -34d04m27s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Rises, but very low: maximum altitude about 5 degrees; needs a clear southern horizon. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Phact
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 40,000ly |
| RA (J2000; approximate centre) | 05h14m06s |
| Declination (J2000; approximate centre) | -40d03m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Berenice's hair, Com
Coma Berenices is one of the 88 IAU-recognised constellations. Its common English description is: Berenice's hair.
| Common English name | Berenice's hair |
|---|---|
| IAU abbreviation | Com |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Beta Comae Berenices |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Beta Comae Berenices |
| Apparent magnitude (V) | 4.25 |
| Spectral type | F9.5V |
| Distance from Earth | About 30ly |
| RA (ICRS / J2000) | 13h11m52s |
| Declination (ICRS / J2000) | +27d52m41s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 67 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Beta Comae Berenices
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 17 million ly |
| RA (J2000; approximate centre) | 12h56m42s |
| Declination (J2000; approximate centre) | +21d41m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 61 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 59,700ly |
| RA (J2000; approximate centre) | 13h12m54s |
| Declination (J2000; approximate centre) | +18d10m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 57 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 40 million ly |
| RA (J2000; approximate centre) | 12h36m18s |
| Declination (J2000; approximate centre) | +25d59m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 65 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Comets
A small body rich in ice, dust and rocky material. Most familiar comets orbit the Sun, although some arrive from interstellar space. When warmed by the Sun, exposed ices can turn directly into gas, carrying dust into a surrounding cloud called a coma. A comet may develop gas and dust tails, generally extending away from the Sun rather than simply trailing behind its motion. A visible tail is not always present.
Sources: NASA: comet facts
One of the 88 officially defined regions of the sky. The name also commonly refers to a familiar star pattern within that region; its stars are not necessarily physically close together.
Other names and search terms: 88 constellations, IAU constellations, Constellation index
All 88 IAU-recognised constellations, with common English names and links to their profiles. Each profile includes a representative brightest star and selected deep-sky objects with distances and RA/Dec coordinates. Serpens has two separated regions but is one constellation.
Visibility key: Yes = the whole constellation can rise above Lewes's horizon; Partly = only part can rise; No = never visible from Lewes. This describes visibility at suitable times of year above an unobstructed horizon, not visibility tonight. Very low objects may be difficult to see.
| Constellation | Common English name | Visible from Lewes? |
|---|---|---|
| Andromeda | Chained maiden | Yes |
| Antlia | Air pump | Partly |
| Apus | Bird of paradise | No |
| Aquarius | Water bearer | Yes |
| Aquila | Eagle | Yes |
| Ara | Altar | No |
| Aries | Ram | Yes |
| Auriga | Charioteer | Yes |
| Bootes | Herdsman | Yes |
| Caelum | Chisel | Partly |
| Camelopardalis | Giraffe | Yes |
| Cancer | Crab | Yes |
| Canes Venatici | Hunting dogs | Yes |
| Canis Major | Greater dog | Yes |
| Canis Minor | Lesser dog | Yes |
| Capricornus | Sea goat | Yes |
| Carina | Keel | No |
| Cassiopeia | Queen | Yes |
| Centaurus | Centaur | Partly |
| Cepheus | King | Yes |
| Cetus | Sea monster (often called the whale) | Yes |
| Chamaeleon | Chameleon | No |
| Circinus | Drawing compasses | No |
| Columba | Dove | Partly |
| Coma Berenices | Berenice's hair | Yes |
| Corona Australis | Southern crown | Partly |
| Corona Borealis | Northern crown | Yes |
| Corvus | Crow | Yes |
| Crater | Cup | Yes |
| Crux | Southern cross | No |
| Cygnus | Swan | Yes |
| Delphinus | Dolphin | Yes |
| Dorado | Dolphinfish | No |
| Draco | Dragon | Yes |
| Equuleus | Little horse | Yes |
| Eridanus | River | Partly |
| Fornax | Furnace | Partly |
| Gemini | Twins | Yes |
| Grus | Crane | Partly |
| Hercules | Hercules (the hero) | Yes |
| Horologium | Pendulum clock | No |
| Hydra | Water snake | Yes |
| Hydrus | Lesser water snake | No |
| Indus | Indian | No |
| Lacerta | Lizard | Yes |
| Leo | Lion | Yes |
| Leo Minor | Lesser lion | Yes |
| Lepus | Hare | Yes |
| Libra | Scales | Yes |
| Lupus | Wolf | Partly |
| Lynx | Lynx | Yes |
| Lyra | Lyre | Yes |
| Mensa | Table mountain | No |
| Microscopium | Microscope | Partly |
| Monoceros | Unicorn | Yes |
| Musca | Fly | No |
| Norma | Carpenter's square | No |
| Octans | Octant | No |
| Ophiuchus | Serpent bearer | Yes |
| Orion | Hunter | Yes |
| Pavo | Peacock | No |
| Pegasus | Winged horse | Yes |
| Perseus | Perseus (the hero) | Yes |
| Phoenix | Phoenix | No |
| Pictor | Painter's easel | No |
| Pisces | Fishes | Yes |
| Piscis Austrinus | Southern fish | Yes |
| Puppis | Stern | Partly |
| Pyxis | Mariner's compass | Yes |
| Reticulum | Reticle (eyepiece grid) | No |
| Sagitta | Arrow | Yes |
| Sagittarius | Archer | Partly |
| Scorpius | Scorpion | Partly |
| Sculptor | Sculptor | Partly |
| Scutum | Shield | Yes |
| Serpens | Serpent | Yes |
| Sextans | Sextant | Yes |
| Taurus | Bull | Yes |
| Telescopium | Telescope | No |
| Triangulum | Triangle | Yes |
| Triangulum Australe | Southern triangle | No |
| Tucana | Toucan | No |
| Ursa Major | Great bear | Yes |
| Ursa Minor | Little bear | Yes |
| Vela | Sails | Partly |
| Virgo | Maiden | Yes |
| Volans | Flying fish | No |
| Vulpecula | Little fox | Yes |
Sources: IAU: all 88 constellations
Other names and search terms: Thermal equilibration, Acclimatisation
The time needed for a telescope's optics and surrounding structure to approach outdoor temperature. Temperature differences can produce air currents and distortions that blur images.
Other names and search terms: Southern crown, CrA
Corona Australis is one of the 88 IAU-recognised constellations. Its common English description is: southern crown.
| Common English name | Southern crown |
|---|---|
| IAU abbreviation | CrA |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Meridiana (Alpha Coronae Australis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Meridiana |
| Latin / catalogue designation | Alpha Coronae Australis |
| Apparent magnitude (V) | 4.09 |
| Spectral type | A2Va |
| Distance from Earth | About 120ly |
| RA (ICRS / J2000) | 19h09m28s |
| Declination (ICRS / J2000) | -37d54m16s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | At most 1.2 degrees above the horizon: exceptionally low and generally impractical. |
Distance is a rounded estimate from the catalogue parallax. The quoted V magnitude is a representative catalogue value, not a live measurement.
Sources: SIMBAD: Meridiana
| Role | Nearly equal brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Beta Coronae Australis |
| Apparent magnitude (V) | 4.09 |
| Spectral type | K0II/IIICNIb |
| Distance from Earth | About 560ly |
| RA (ICRS / J2000) | 19h10m02s |
| Declination (ICRS / J2000) | -39d20m27s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Beta Coronae Australis
| Object type | Reflection Nebula |
|---|---|
| Distance from Earth | 400ly |
| RA (J2000; approximate centre) | 19h01m54s |
| Declination (J2000; approximate centre) | -36d57m00s |
| Visibility from Lewes | At most 2.2 degrees above the horizon: exceptionally low and generally impractical. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 22,000ly |
| RA (J2000; approximate centre) | 18h08m00s |
| Declination (J2000; approximate centre) | -43d42m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye. Alpha and Beta are effectively tied near magnitude 4.1.
Sources: IAU: the 88 constellations
Other names and search terms: Northern crown, CrB
Corona Borealis is one of the 88 IAU-recognised constellations. Its common English description is: northern crown.
| Common English name | Northern crown |
|---|---|
| IAU abbreviation | CrB |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Alphecca (Alpha Coronae Borealis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Alphecca |
| Latin / catalogue designation | Alpha Coronae Borealis |
| Apparent magnitude (V) | 2.24 |
| Spectral type | A1IV |
| Distance from Earth | About 77ly |
| RA (ICRS / J2000) | 15h34m41s |
| Declination (ICRS / J2000) | +26d42m53s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 66 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alphecca
| Object type | Galaxy cluster |
|---|---|
| Distance from Earth | About 1,100 million ly (redshift-based luminosity distance) |
| RA (J2000; approximate centre) | 15h22m23s |
| Declination (J2000; approximate centre) | +27d44m20s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 67 degrees. |
An indicative distance calculated from SIMBAD redshift z=0.0731, using H0=70km/s/Mpc and a flat cosmology with matter density parameter 0.3. This is a luminosity distance, not a direct measurement; local galaxy motions can cause substantial uncertainty, especially at low redshift.
Sources: SIMBAD: Abell 2065
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Corrector plate, Schmidt corrector plate
An optical element used to reduce aberrations. In an SCT, the thin front Schmidt corrector plate corrects the combined optical system; it is not the main focusing objective lens of a refractor.
Other names and search terms: Crow, Crv
Corvus is one of the 88 IAU-recognised constellations. Its common English description is: crow.
| Common English name | Crow |
|---|---|
| IAU abbreviation | Crv |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Gienah (Gamma Corvi) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Gienah |
| Latin / catalogue designation | Gamma Corvi |
| Apparent magnitude (V) | 2.58 |
| Spectral type | B8III |
| Distance from Earth | About 150ly |
| RA (ICRS / J2000) | 12h15m48s |
| Declination (ICRS / J2000) | -17d32m31s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 22 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Gienah
| Object type | Interacting spiral galaxy; one of the Antennae pair |
|---|---|
| Distance from Earth | About 65 million ly |
| RA (J2000; approximate centre) | 12h01m54s |
| Declination (J2000; approximate centre) | -18d52m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 20 degrees. |
One of two interacting galaxies known as the Antennae. This coordinate identifies this galaxy's approximate centre. Published distances differ; the value shown follows NASA's Caldwell reference.
Sources: NASA: Antennae Galaxies (C60/61); NGC 2000.0 position catalogue
| Object type | Interacting spiral galaxy; one of the Antennae pair |
|---|---|
| Distance from Earth | About 65 million ly |
| RA (J2000; approximate centre) | 12h01m54s |
| Declination (J2000; approximate centre) | -18d53m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 20 degrees. |
One of two interacting galaxies known as the Antennae. This coordinate identifies this galaxy's approximate centre. Published distances differ; the value shown follows NASA's Caldwell reference.
Sources: NASA: Antennae Galaxies (C60/61); NGC 2000.0 position catalogue
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: CMB
Faint microwave radiation left from the early Universe, released when the Universe became transparent about 380,000 years after the Big Bang. Its tiny temperature variations provide evidence about cosmic history and composition. Planck measured it in great detail.
Sources: ESA: Planck
A weight used to balance a telescope or reduce an unbalanced load on its mount. Some strain-wave mounts can carry specified loads without one, but heavier loads may require one.
Other names and search terms: Cup, Crt
Crater is one of the 88 IAU-recognised constellations. Its common English description is: cup.
| Common English name | Cup |
|---|---|
| IAU abbreviation | Crt |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Delta Crateris |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Delta Crateris |
| Apparent magnitude (V) | 3.56 |
| Spectral type | G9IIICH0.5 |
| Distance from Earth | About 190ly |
| RA (ICRS / J2000) | 11h19m20s |
| Declination (ICRS / J2000) | -14d46m43s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 24 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Delta Crateris
| Object type | Galaxy |
|---|---|
| Distance from Earth | About 53 million ly (redshift-based luminosity distance) |
| RA (J2000; approximate centre) | 11h03m24s |
| Declination (J2000; approximate centre) | -23d05m12s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 16 degrees. |
An indicative distance calculated from SIMBAD redshift z=0.003751, using H0=70km/s/Mpc and a flat cosmology with matter density parameter 0.3. This is a luminosity distance, not a direct measurement; local galaxy motions can cause substantial uncertainty, especially at low redshift.
Sources: SIMBAD: NGC 3511
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Southern cross, Cru
Crux is one of the 88 IAU-recognised constellations. Its common English description is: southern cross. Its brightest entry uses the combined light of the Acrux multiple system.
| Common English name | Southern cross |
|---|---|
| IAU abbreviation | Cru |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Acrux (Alpha Crucis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Acrux |
| Latin / catalogue designation | Alpha Crucis |
| Apparent magnitude (V) | 0.77 |
| Spectral type | B0.5IV+B1V |
| Distance from Earth | About 320ly |
| RA (ICRS / J2000) | 12h26m36s |
| Declination (ICRS / J2000) | -63d05m57s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax. Magnitude and spectral type refer to the unresolved multiple system.
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 6,500ly |
| RA (J2000; approximate centre) | 12h53m36s |
| Declination (J2000; approximate centre) | -60d20m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Mars Science Laboratory, MSL
NASA's Mars Science Laboratory rover, which landed in Gale Crater in August 2012. Its mobile laboratory examines rocks and chemistry to investigate whether ancient Mars had environments suitable for microbial life. Evidence of past habitability is not the same as discovery of life.
| Programme / agency | NASA / JPL |
|---|---|
| Key dates | Launched 2011; landed 2012 |
| Destination / science location | Gale Crater, Mars |
Sources: Official or institutional reference: Curiosity rover
Other names and search terms: Swan, Cyg
Cygnus is one of the 88 IAU-recognised constellations. Its common English description is: swan.
| Common English name | Swan |
|---|---|
| IAU abbreviation | Cyg |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Deneb (Alpha Cygni) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Deneb |
| Latin / catalogue designation | Alpha Cygni |
| Apparent magnitude (V) | 1.25 |
| Spectral type | A2Ia |
| Distance from Earth | About 2,600ly (uncertain) |
| RA (ICRS / J2000) | 20h41m26s |
| Declination (ICRS / J2000) | +45d16m49s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 84 degrees. |
Distance estimates for this supergiant differ substantially. This is the roughly 802pc association-based estimate, rather than the shorter Hipparcos parallax estimate.
Sources: SIMBAD: Deneb; Deneb distance discussion: Chesneau et al. (2010)
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | 61 Cygni A |
| System or component described | Individual component |
| Apparent magnitude (V) | 5.21 |
| Spectral type | K5V |
| Distance from Earth | About 11.4ly |
| RA (ICRS / J2000) | 21h06m54s |
| Declination (ICRS / J2000) | +38d44m58s |
| System structure | One component of the nearby 61 Cygni binary; both stars are cool K-type dwarfs. |
| Observing interest | A comparatively wide orange pair, suitable for small telescopes. The system was an early milestone in measuring stellar parallax. |
| Visibility from Lewes | Visible at a suitable season and time; maximum altitude about 78 degrees. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate.
Sources: SIMBAD: 61 Cygni A
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | 61 Cygni B |
| System or component described | Individual component |
| Apparent magnitude (V) | 6.03 |
| Spectral type | K7V |
| Distance from Earth | About 11.4ly |
| RA (ICRS / J2000) | 21h06m55s |
| Declination (ICRS / J2000) | +38d44m31s |
| System structure | One component of the nearby 61 Cygni binary; both stars are cool K-type dwarfs. |
| Observing interest | A comparatively wide orange pair, suitable for small telescopes. The system was an early milestone in measuring stellar parallax. |
| Visibility from Lewes | Visible at a suitable season and time; maximum altitude about 78 degrees. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate.
Sources: SIMBAD: 61 Cygni B
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Albireo A |
| Latin / catalogue designation | Beta1 Cygni |
| System or component described | Named visual component; A itself contains an unresolved close pair |
| Apparent magnitude (V) | 3.08 |
| Spectral type | K3II+B9.5V |
| Distance from Earth | About 363ly |
| RA (ICRS / J2000) | 19h30m43s |
| Declination (ICRS / J2000) | +27d57m35s |
| System structure | Part of the celebrated Albireo visual double; the bright A component is itself a close binary. |
| Observing interest | An accessible golden and blue contrasting pair. The wide A/B pairing should not be presented as a securely established physical binary. |
| Visibility from Lewes | Visible at a suitable season and time; maximum altitude about 67 degrees. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate. Published studies favour an unbound or uncertain wide association. Separate catalogue distances are given for the two visual components; multiplicity complicates the bright component's astrometry.
Sources: SIMBAD: Albireo A; Bastian and Anton (2018): Albireo physical status
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Albireo B |
| Latin / catalogue designation | Beta2 Cygni |
| System or component described | Named visual component; A itself contains an unresolved close pair |
| Apparent magnitude (V) | 5.11 |
| Spectral type | B8Ve |
| Distance from Earth | About 398ly |
| RA (ICRS / J2000) | 19h30m45s |
| Declination (ICRS / J2000) | +27d57m55s |
| System structure | Part of the celebrated Albireo visual double; the bright A component is itself a close binary. |
| Observing interest | An accessible golden and blue contrasting pair. The wide A/B pairing should not be presented as a securely established physical binary. |
| Visibility from Lewes | Visible at a suitable season and time; maximum altitude about 67 degrees. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate. Published studies favour an unbound or uncertain wide association. Separate catalogue distances are given for the two visual components; multiplicity complicates the bright component's astrometry.
Sources: SIMBAD: Albireo B; Bastian and Anton (2018): Albireo physical status
| Object type | Emission Nebula |
|---|---|
| Distance from Earth | 1,800ly |
| RA (J2000; approximate centre) | 20h58m48s |
| Declination (J2000; approximate centre) | +44d20m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 83 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Nebula, Supernova Remnant |
|---|---|
| Distance from Earth | 2,000ly |
| RA (J2000; approximate centre) | 20h56m24s |
| Declination (J2000; approximate centre) | +31d43m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 71 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 4,700ly |
| RA (J2000; approximate centre) | 20h12m00s |
| Declination (J2000; approximate centre) | +38d21m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 77 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Jocelyn Bell Burnell, Jocelyn Bell
A Northern Irish astrophysicist who identified the first pulsar signals in 1967 while a Cambridge research student working with Antony Hewish. Her careful inspection of radio chart recordings revealed a new class of rapidly rotating neutron stars. She has also made major contributions to science education and inclusion.
| Dates | Born 1943; pulsar discovery 1967 |
|---|---|
| Background | Northern Irish astrophysicist |
Sources: Official or institutional reference: Dame Jocelyn Bell Burnell
Other names and search terms: Night vision
The gradual increase in your eyes' sensitivity after entering darkness. Bright lights disrupt it. A dim red torch can help preserve adaptation, but even red light should be kept faint.
Other names and search terms: Dawes limit
An approximate double-star resolution guide: divide 116 by the aperture in millimetres to obtain a separation in arcseconds. It applies to suitable, similarly bright double stars under good conditions, not every kind of detail.
Other names and search terms: Dec
The celestial equivalent of latitude: angular distance north or south of the celestial equator. It runs from -90 degrees at the south celestial pole, through 0 degrees on the celestial equator, to +90 degrees at the north celestial pole. A plus sign means north and a minus sign means south. Degrees can be divided into arcminutes and arcseconds. Paired with right ascension, declination locates an object on the sky.
Other names and search terms: Dec axis
The axis of an equatorial mount that changes the telescope's declination. It is perpendicular to the polar axis.
Other names and search terms: DSO, Deep sky
An astronomical object beyond the Solar System, such as a star cluster, nebula or galaxy. These objects vary greatly in angular size and brightness, so no single magnification suits them all.
Other names and search terms: Dolphin, Del
Delphinus is one of the 88 IAU-recognised constellations. Its common English description is: dolphin.
| Common English name | Dolphin |
|---|---|
| IAU abbreviation | Del |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Rotanev (Beta Delphini) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Rotanev |
| Latin / catalogue designation | Beta Delphini |
| Apparent magnitude (V) | 3.63 |
| Spectral type | F5IV |
| Distance from Earth | About 100ly |
| RA (ICRS / J2000) | 20h37m33s |
| Declination (ICRS / J2000) | +14d35m42s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 54 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Rotanev
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 135,000ly |
| RA (J2000; approximate centre) | 21h01m30s |
| Declination (J2000; approximate centre) | +16d11m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 55 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 50,000ly |
| RA (J2000; approximate centre) | 20h34m12s |
| Declination (J2000; approximate centre) | +07d24m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 47 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
In photography, the range of distances in a scene that appears acceptably sharp. A lower f-number usually gives a shallower depth of field when other relevant factors are comparable. It is different from depth of focus.
Other names and search terms: Focus tolerance
The small range of positions around the focal plane over which an eyepiece or camera can still give an acceptably sharp image. Lower focal ratios generally require more precise focusing.
Water droplets that condense on a surface when it becomes cold enough. Dew on optics degrades the view; suitable dew shields or heaters can help. Do not rub moisture from an optical surface.
An extension around the front of a telescope that helps delay dew formation and can reduce stray light. It does not guarantee dew-free optics; a suitable heater may also be needed.
The spreading of light caused by its wave nature when it passes an aperture or obstruction. Diffraction sets a fundamental limit on a telescope's ability to separate very close detail.
Other names and search terms: Dob, Light bucket
An economical, stable form of alt-azimuth mounting, usually carrying a Newtonian reflector. The name describes the mounting arrangement. Many are manually moved, although motorised versions exist. Large examples are often called light buckets.
Other names and search terms: Dolphinfish, Dor
Dorado is one of the 88 IAU-recognised constellations. Its common English description is: dolphinfish.
| Common English name | Dolphinfish |
|---|---|
| IAU abbreviation | Dor |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Alpha Doradus |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Doradus |
| Apparent magnitude (V) | 3.28 |
| Spectral type | B8IIIpSi |
| Distance from Earth | About 170ly |
| RA (ICRS / J2000) | 04h34m00s |
| Declination (ICRS / J2000) | -55d02m42s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Doradus
| Object type | Nebula |
|---|---|
| Distance from Earth | 170,000ly |
| RA (J2000; approximate centre) | 05h38m36s |
| Declination (J2000; approximate centre) | -69d05m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Binary star targets, Double star targets, Multiple star targets
A selection of interesting doubles and multiple stars in the constellation profiles. Follow a name to its constellation entry for distance, coordinates, spectral type and observing notes. The list includes a visual double whose physical association is uncertain, as well as established physical systems. A telescope does not necessarily reveal every star in a multiple system.
| Star / multiple system | Constellation and observing notes |
|---|---|
| Almach | Andromeda: A colourful hierarchical multiple. |
| Izar | Bootes: A close, unequal colour-contrast binary. |
| Achird | Cassiopeia: A contrasting nearby binary. |
| Alpha Centauri and Proxima Centauri | Centaurus: A nearby triple, below the Lewes horizon. |
| Sirius | Canis Major: A bright star with a challenging white-dwarf companion. |
| Cor Caroli | Canes Venatici: A wide, attractive visual pair. |
| Albireo | Cygnus: A striking visual double whose wide physical association is uncertain. |
| 61 Cygni | Cygnus: A nearby pair of cool dwarf stars. |
| Castor | Gemini: A six-star system, seen telescopically as fewer points. |
| Algieba | Leo: A close golden giant-star binary. |
| Epsilon Lyrae (Double Double) | Lyra: Two close binaries forming four principal stars. |
| Beta Monocerotis | Monoceros: A rewarding visual triple. |
| Mizar and Alcor | Ursa Major: A famous wide association containing six stars. |
| Polaris | Ursa Minor: The Pole Star is a triple, with one accessible wide companion. |
| Porrima | Virgo: A near-equal binary with changing angular separation. |
Two stars that appear close together in the sky. They may form a physical binary, with both stars bound by gravity, or an optical double, produced by an apparent alignment. A pleasing telescopic pair is not automatically a gravitationally bound system. Resolving close pairs depends on their angular separation, brightness contrast, telescope aperture and atmospheric seeing.
Sources: NASA: seeing double stars
Other names and search terms: Dragon, Dra
Draco is one of the 88 IAU-recognised constellations. Its common English description is: dragon.
| Common English name | Dragon |
|---|---|
| IAU abbreviation | Dra |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Eltanin (Gamma Draconis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Eltanin |
| Latin / catalogue designation | Gamma Draconis |
| Apparent magnitude (V) | 2.23 |
| Spectral type | K5III |
| Distance from Earth | About 150ly |
| RA (ICRS / J2000) | 17h56m36s |
| Declination (ICRS / J2000) | +51d29m20s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 89 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Eltanin
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 3,000ly |
| RA (J2000; approximate centre) | 17h58m36s |
| Declination (J2000; approximate centre) | +66d38m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 74 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Lenticular Galaxy |
|---|---|
| Distance from Earth | 44 million ly |
| RA (J2000; approximate centre) | 15h06m30s |
| Declination (J2000; approximate centre) | +55d46m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 85 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Under the IAU Solar System definition, a body orbiting the Sun that is nearly round through its own gravity, is not a moon, and has not gravitationally cleared the neighbourhood of its orbit. Pluto and Ceres are examples. Dwarf planets are a separate category from the eight planets, rather than simply smaller members of that group.
Sources: IAU: dwarf-planet definition
Our home planet, with liquid-water oceans and one natural satellite, the Moon. Its axial tilt is the main cause of the seasons, rather than its changing distance from the Sun.
| Position from the Sun | 3 of 8 |
|---|---|
| Type | Rocky (terrestrial) planet |
| Average Sun distance (semi-major axis) | 149,598,000km (1.000AU) |
| Orbital period (sidereal year) | 365.256 Earth days (1.00 Earth years) |
| Approximate orbit circumference | 940,000,000km |
| Mean diameter | 12,742km |
| Rotation relative to the stars | 23.9345h (23h56min); prograde |
| Mean solar day | 24h |
| Axial tilt (obliquity) | 23.44 degrees |
| Orbit inclination to the ecliptic | 0 degrees |
| Orbital eccentricity | 0.0167 |
| Perihelion (nearest Sun distance) | 147,095,000km |
| Aphelion (farthest Sun distance) | 152,100,000km |
| Known moons | 1 (JPL count checked 25 October 2026) |
Values are approximate. Average distance means semi-major axis; mean diameter is not necessarily the equatorial diameter. Orbit circumference is a calculated ellipse approximation. Orbital elements change with time, and moon counts change as discoveries are recognised.
Sources: NASA Earth fact sheet; JPL recognised planetary satellites
Other names and search terms: Orbital eccentricity
A dimensionless measure of orbital shape, written e. A circular orbit has e = 0; a bound elliptical orbit has 0 < e < 1, with larger values giving a more elongated ellipse. Eccentricity describes shape, not the tilt of an orbit.
A binary whose orbital plane is aligned so that, from our viewpoint, one star periodically passes in front of the other. The resulting dips in combined brightness reveal eclipses. A system may be both an eclipsing binary and a spectroscopic binary.
Other names and search terms: Ecliptic plane
The Sun's apparent yearly path against the background stars, corresponding to the plane of Earth's orbit projected onto the celestial sphere. It is tilted by about 23.4 degrees to the celestial equator. The Moon and planets usually appear near it because their orbital planes are close to Earth's. Its northward crossing of the celestial equator is the First Point of Aries. The ecliptic plane is the reference for the planetary inclinations listed here.
Other names and search terms: Halley, Edmund Halley
An English astronomer who recognised that several recorded comet appearances represented the same returning object and predicted its next return. Halley's Comet was named in his honour. He also catalogued southern stars and became the second Astronomer Royal.
| Dates | 1656-1742 |
|---|---|
| Background | English astronomer |
Other names and search terms: Hubble
An American astronomer who used Cepheid variables to establish that the Andromeda system lies beyond the Milky Way. His observational work on galaxy distances and recession velocities helped establish cosmic expansion. Hubble Space Telescope is named after him; the wider discovery also involved work by Georges Lemaitre, Vesto Slipher and others.
| Dates | 1889-1953 |
|---|---|
| Background | American astronomer; Mount Wilson Observatory |
The focal length of the complete optical system, including any elements that change its image scale. In a compound telescope it is not simply the tube length or the sum of the folded light-path distances.
Other names and search terms: Stellar temperature
The temperature of an ideal blackbody that would emit the same total power per unit surface area as a star. It describes the star's overall radiation, not its core temperature. The Sun's effective temperature is about 5,772K.
Other names and search terms: Effelsberg Observatory
A major fully steerable single-dish radio telescope operated by the Max Planck Institute for Radio Astronomy. It studies pulsars, interstellar material and galaxies and can join very-long-baseline networks.
| Location | Near Bad Munstereifel, North Rhine-Westphalia, Germany |
|---|---|
| Main instruments | 100m fully steerable dish |
| Observing wavelengths | Radio |
Sources: Official or institutional reference: Effelsberg Radio Telescope
The full range of electromagnetic radiation: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. All are forms of light, but human eyes detect only the visible part. Astronomers use different instruments to study different parts of the spectrum.
Other names and search terms: EAA
Observing with a camera and electronic display, often combining short exposures to reveal faint objects as the session progresses. A smart telescope is one way to do this; conventional telescopes and cameras can also be used.
A cloud of gas that produces its own light after receiving energy, often from nearby hot stars. Many familiar examples are star-forming regions; planetary nebulae are also emission nebulae, with a different origin.
A mount with its polar axis aligned parallel to Earth's rotation axis. It can follow the sky's daily motion mainly by turning around this one axis, manually or with a motor.
Other names and search terms: Wedge
A tilted support that allows a suitable fork-mounted telescope to operate equatorially by aligning the base's rotation axis with Earth's rotation axis.
Other names and search terms: Little horse, Equ
Equuleus is one of the 88 IAU-recognised constellations. Its common English description is: little horse.
| Common English name | Little horse |
|---|---|
| IAU abbreviation | Equ |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Kitalpha (Alpha Equulei) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Kitalpha |
| Latin / catalogue designation | Alpha Equulei |
| Apparent magnitude (V) | 3.93 |
| Spectral type | G6IV+B9.5V |
| Distance from Earth | About 190ly |
| RA (ICRS / J2000) | 21h15m49s |
| Declination (ICRS / J2000) | +05d14m52s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 44 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Kitalpha
| Object type | Galaxy |
|---|---|
| Distance from Earth | About 230 million ly (redshift-based luminosity distance) |
| RA (J2000; approximate centre) | 21h05m37s |
| Declination (J2000; approximate centre) | +11d24m51s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 51 degrees. |
An indicative distance calculated from SIMBAD redshift z=0.016278, using H0=70km/s/Mpc and a flat cosmology with matter density parameter 0.3. This is a luminosity distance, not a direct measurement; local galaxy motions can cause substantial uncertainty, especially at low redshift.
Sources: SIMBAD: NGC 7015
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: River, Eri
Eridanus is one of the 88 IAU-recognised constellations. Its common English description is: river.
| Common English name | River |
|---|---|
| IAU abbreviation | Eri |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Achernar (Alpha Eridani) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Achernar |
| Latin / catalogue designation | Alpha Eridani |
| Apparent magnitude (V) | 0.46 |
| Spectral type | B6Vpe |
| Distance from Earth | About 140ly |
| RA (ICRS / J2000) | 01h37m43s |
| Declination (ICRS / J2000) | -57d14m12s |
| Among the ten brightest night-sky stars? | Yes: reference rank 9 (Sun excluded). |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Achernar; ESA Hipparcos brightness reference
| Object type | Barred spiral galaxy |
|---|---|
| Distance from Earth | About 69 million ly |
| RA (J2000; approximate centre) | 03h19m41s |
| Declination (J2000; approximate centre) | -19d24m40s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 20 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 1300; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Euclid space telescope
An ESA space telescope surveying galaxies to investigate the large-scale structure and expansion of the Universe, including the effects of dark matter and dark energy.
| Agency or partnership | ESA and the Euclid scientific collaboration |
|---|---|
| Science orbit / location | Sun-Earth L2 region |
| Main telescope or instruments | 1.2m telescope; visible imager and near-infrared imaging/spectroscopy instrument |
| Observing wavelengths | Visible and near-infrared |
| Mission history | Launched in 2023 |
| Scientific importance | A wide survey of galaxy shapes and distances to study cosmic structure |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Sources: ESA: Euclid overview
The smallest Galilean moon of Jupiter. Its fractured icy surface covers what is strongly thought to be a global salty ocean. Liquid water, chemical ingredients and an energy supply make it an important target in the search for potentially habitable environments; life has not been detected.
| Parent planet | Jupiter |
|---|---|
| Order among the Galilean moons | 2 from Jupiter |
| Mean diameter | About 3,122km |
| Orbital distance (semi-major axis) | 671,100km from the planet's centre |
| Orbital period | 3.55118 Earth days |
| Rotation period | 3.55118 Earth days; synchronous with its orbit |
| Composition | Rocky interior beneath a water-ice shell |
Values are approximate reference figures. Orbital distance is measured from the centre of the parent planet, not its cloud tops. The rotation period is relative to distant stars, not the interval between sunrises. These moving Solar System objects have no single fixed RA/Dec position or distance from Earth.
Sources: NASA: Europa facts; NASA satellite fact sheet (orbital parameters); JPL: satellite physical parameters (mean radii)
Other names and search terms: ESO
An intergovernmental organisation that builds and operates major ground-based astronomical facilities, particularly in Chile. The UK is a member. ESO operates the Very Large Telescope and is a partner in ALMA, supporting astronomers with telescopes, instruments and data.
| Area or location | European organisation; major observatory sites in Chile |
|---|---|
| Role | Intergovernmental ground-based astronomy organisation |
| Useful for | Observatory information, astronomical images and research results |
Sources: Official organisation information
Other names and search terms: ESA
An intergovernmental organisation coordinating European space research, missions and technology. Its member countries include the UK. ESA develops astronomy and planetary missions, Earth-observation spacecraft and other space capabilities, often with international partners.
| Area or location | Europe; headquarters in Paris, France |
|---|---|
| Role | Intergovernmental space agency |
| Useful for | European missions, educational resources and scientific data |
Sources: Official organisation information
The diameter of the beam of light leaving an eyepiece. Calculate it by dividing telescope aperture by magnification, using millimetres. If it exceeds your eye's pupil, some collected light misses your eye.
Other names and search terms: Extrasolar planet
A planet outside our Solar System. Exoplanets can be detected in several ways, including small dips in a star's brightness during transits and changes in stellar motion. Finding a planet does not by itself establish that it is habitable or inhabited.
Sources: NASA: Kepler discoveries
Other names and search terms: Explorer I
The first successful United States satellite. Launched in 1958, its radiation measurements helped establish the existence of the Van Allen radiation belts around Earth.
| Programme / agency | United States: Army Ballistic Missile Agency and JPL |
|---|---|
| Key dates | Launched 1958 |
| Destination / science location | Earth orbit |
Other names and search terms: Exposure time
The interval during which a camera records light for one image. A longer exposure gathers more light, but tracking errors, bright sky and sensor saturation can limit how long it can usefully be.
The distance from the eyepiece's last optical surface to the position where your eye sees its full field. Adequate eye relief is especially useful for observers who wear glasses.
Other names and search terms: Ocular
The optical assembly through which you examine the image formed by a telescope. Its focal length, together with the telescope's focal length, determines magnification.
The focal length marked on an eyepiece, usually in millimetres. On the same telescope, a shorter eyepiece focal length gives higher magnification and a longer one gives lower magnification.
Other names and search terms: Fast telescope, Slow telescope
Terms describing focal ratio. A low f-number is fast and a high one is slow. For imaging extended objects with the same camera, a faster system gives greater sensor illumination; visual brightness also depends on exit pupil and transmission.
Other names and search terms: FAS
An umbrella organisation supporting astronomical societies, clubs and amateur groups across the UK. It helps societies work together through shared resources, practical guidance, meetings and representation.
| Area or location | United Kingdom |
|---|---|
| Role | Federation of astronomy societies |
| Useful for | Support for running a society, outreach and connections between groups |
Sources: Official organisation information
Other names and search terms: Fermi, Fermi telescope
A NASA-led mission surveying the high-energy gamma-ray sky. It studies extreme processes involving pulsars, stellar explosions, active galaxies and other energetic sources.
| Agency or partnership | NASA, with international partners |
|---|---|
| Science orbit / location | Low Earth orbit |
| Main telescope or instruments | Large Area Telescope (LAT) and Gamma-ray Burst Monitor (GBM); particle-interaction detectors rather than an ordinary optical mirror |
| Observing wavelengths | Gamma rays, with overlapping high-energy coverage in its instruments |
| Mission history | Launched in 2008 |
| Scientific importance | Wide-field monitoring of gamma-ray bursts and other energetic or variable sources |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Sources: NASA: Fermi; NASA: Fermi instruments
Other names and search terms: FOV
The angular extent of the view. True field describes the patch of sky visible; apparent field describes how wide an eyepiece's view looks to your eye. Camera field of view also depends on sensor size.
The turning of a star pattern relative to a camera as an alt-azimuth mount tracks the sky. It can smear longer exposures even when the target stays centred. Correct equatorial tracking avoids this particular rotation.
Adjusting a finder so that its aiming mark points at the same distant target as the main telescope. Use a safe target well away from the Sun. This does not align the telescope's internal optics.
Other names and search terms: Finderscope, Finder
A small telescope attached to the main telescope, normally giving a wider, lower-power view to help aim it. A red-dot finder instead projects an aiming mark against your direct view of the sky.
The point where the ecliptic crosses the celestial equator from south to north: the direction of the Sun at the March equinox. It defines right ascension 0h, equivalent to 0 degrees, and declination 0 degrees. Its historical name dates from when the point lay in Aries; precession has moved it into Pisces. Coordinates tied to a reference equinox, such as J2000.0, use that equinox's reference direction rather than continually moving the coordinate grid.
A measure of an optical system's image scale, normally stated in millimetres. For a simple lens it is the distance from its optical principal plane to the focus for a distant object. With the same eyepiece, longer telescope focal lengths give higher power and narrower true fields.
The plane where a telescope forms its focused image. A camera sensor is placed there for imaging; an eyepiece is positioned to let your eye examine that image.
Other names and search terms: F-ratio, F-number, f/number
Telescope focal length divided by aperture, expressed in matching units: a 1,000 mm focal length and 200 mm aperture give f/5. It describes the optical geometry, not overall quality or visual magnification by itself.
Other names and search terms: Focal point, Focusing
The condition in which the optics form a sharp image. Light from a distant point is brought to a focal point; points across an extended object form an image near the focal plane. Focusing adjusts the optical spacing to make the view sharp.
Other names and search terms: Drawtube
The mechanism used to achieve sharp focus, often by moving the eyepiece or camera in a drawtube. Some telescopes instead focus by moving a primary mirror. Focusing does not act as a zoom control.
A mounting arrangement that supports a telescope tube between two arms; some related designs use one arm. Forks commonly operate on an alt-azimuth base, or equatorially when a suitable wedge is fitted.
Other names and search terms: Furnace, For
Fornax is one of the 88 IAU-recognised constellations. Its common English description is: furnace.
| Common English name | Furnace |
|---|---|
| IAU abbreviation | For |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Dalim (Alpha Fornacis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Dalim |
| Latin / catalogue designation | Alpha Fornacis |
| Apparent magnitude (V) | 3.98 |
| Spectral type | F6V |
| Distance from Earth | About 46ly |
| RA (ICRS / J2000) | 03h12m05s |
| Declination (ICRS / J2000) | -28d59m15s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Rises, but very low: maximum altitude about 10 degrees; needs a clear southern horizon. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Dalim
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 45 million ly |
| RA (J2000; approximate centre) | 02h46m18s |
| Declination (J2000; approximate centre) | -30d17m00s |
| Visibility from Lewes | Rises, but very low: maximum altitude about 9 degrees; needs a clear southern horizon. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Gaia space observatory
An ESA astrometry mission that measured stellar positions, parallaxes, motions and other properties to build an exceptionally detailed map of the Milky Way. Its data underpin many stellar distances used in astronomical reference works.
| Agency or partnership | ESA |
|---|---|
| Science orbit / location | Science observations around Sun-Earth L2; later sent into a retirement orbit around the Sun |
| Main telescope or instruments | Two telescopes with approximately 1.45m x 0.50m rectangular entrance pupils feeding a shared focal plane |
| Observing wavelengths | Optical astrometry, photometry and spectroscopy |
| Mission history | Launched in 2013; science observations ended in January 2025; spacecraft retired in March 2025 |
| Scientific importance | Three-dimensional mapping of stars and measurements of their motions and physical properties |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Sources: ESA: Gaia mission; ESA: Gaia telescopes and retirement; ESA: Gaia optical design
A vast system of stars, gas, dust and dark matter held together by gravity. Our galaxy is the Milky Way. Other galaxies often appear as faint patches through an eyepiece.
The four large moons of Jupiter observed by Galileo Galilei in 1610: Io, Europa, Ganymede and Callisto, in order outwards from Jupiter. Their motion showed that some celestial bodies orbit something other than Earth. They can often be seen as small points beside Jupiter through binoculars or a small telescope, although a moon may be hidden behind Jupiter or lost in its glare.
Sources: NASA: Jupiter moons
Other names and search terms: Galilean design, Galilean telescope, Galilean refractor
A refracting telescope design with a converging objective and a diverging eyepiece. In the simplest version, the objective is a convex lens and the eyepiece is a concave lens. The eyepiece intercepts the converging light before it reaches the objective's focal point, so no real intermediate image forms between the lenses. Viewed straight through, it gives an upright image without extra image-erecting optics, but its field of view is generally narrow. Galileo used this arrangement for his early astronomical observations. Unlike the Keplerian design, its eyepiece spreads the converging rays apart rather than examining an image already formed by the objective.
| Objective | Converging (positive optical power); convex in the simplest two-lens design. |
|---|---|
| Eyepiece | Diverging (negative optical power); concave in the simplest design. |
| Eyepiece position | Before the objective's focal point, intercepting the light before the rays cross. |
| Straight-through view | Upright; generally a narrow field of view. |
Sources: Museo Galileo: Galilean and Keplerian optical arrangements
Other names and search terms: Galileo
An Italian astronomer who first used improved telescopes to investigate the sky from 1609. His observations of Jupiter's four large moons, the phases of Venus and the Moon's rugged surface challenged established views. He did not invent the telescope and was among several early telescopic observers.
| Dates | 1564-1642 |
|---|---|
| Background | Italian astronomer and physicist |
Sources: Official or institutional reference: Galileo Galilei
Other names and search terms: Galileo spacecraft, Galileo orbiter
NASA mission comprising a Jupiter orbiter and an atmospheric entry probe. The entry probe measured Jupiter's atmosphere in December 1995; the orbiter studied the planet and its moons until a planned entry into Jupiter in 2003. Its observations provided strong evidence for a subsurface ocean on Europa.
| Programme / agency | NASA / JPL |
|---|---|
| Key dates | Launched 1989; Jupiter operations 1995-2003 |
| Destination / science location | Jupiter system |
Sources: Official or institutional reference: Galileo Jupiter probe
Other names and search terms: Galileo GNSS, European satellite navigation
Europe's civilian global satellite-navigation system. Its satellites broadcast precise timing and orbital information so receivers can determine position. It is separate from NASA's Galileo probe to Jupiter and from the astronomer Galileo Galilei.
| Programme / agency | European Union; ESA developed the system |
|---|---|
| Key dates | Initial services began 2016 |
| Destination / science location | Earth orbit |
Sources: Official or institutional reference: Galileo navigation satellites
Very high-energy electromagnetic radiation. Gamma-ray astronomy studies extreme events and particles, including stellar explosions, pulsars and energetic activity around black holes. Instruments generally detect the photons through interactions in specialised detectors rather than ordinary focusing mirrors.
Sources: NASA: Fermi
The largest moon in the Solar System, greater in diameter than Mercury but much less massive. Jupiter's third Galilean moon is the only moon known to generate its own substantial magnetic field. There is strong evidence for a buried saltwater ocean.
| Parent planet | Jupiter |
|---|---|
| Order among the Galilean moons | 3 from Jupiter |
| Mean diameter | About 5,262km |
| Orbital distance (semi-major axis) | 1,070,400km from the planet's centre |
| Orbital period | 7.15455 Earth days |
| Rotation period | 7.15455 Earth days; synchronous with its orbit |
| Composition | Rock and water ice, with a metallic core |
Values are approximate reference figures. Orbital distance is measured from the centre of the parent planet, not its cloud tops. The rotation period is relative to distant stars, not the interval between sunrises. These moving Solar System objects have no single fixed RA/Dec position or distance from Earth.
Sources: NASA: Ganymede facts; NASA satellite fact sheet (orbital parameters); JPL: satellite physical parameters (mean radii)
A giant planet composed mainly of hydrogen and helium, with no ordinary solid surface to stand on. Jupiter and Saturn are gas giants. Despite the name, much of their interiors is dense fluid rather than a thin gas.
Other names and search terms: Twins, Gem
Gemini is one of the 88 IAU-recognised constellations. Its common English description is: twins.
| Common English name | Twins |
|---|---|
| IAU abbreviation | Gem |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Pollux (Beta Geminorum) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Pollux |
| Latin / catalogue designation | Beta Geminorum |
| Apparent magnitude (V) | 1.14 |
| Spectral type | K0IIIb |
| Distance from Earth | About 34ly |
| RA (ICRS / J2000) | 07h45m19s |
| Declination (ICRS / J2000) | +28d01m34s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 67 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Pollux
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Castor |
| Latin / catalogue designation | Alpha Geminorum |
| System or component described | Catalogue reference position and light of the named object; unresolved companions may contribute. |
| Apparent magnitude (V) | 1.58 |
| Spectral type | A1V+A2Vm |
| Distance from Earth | About 50.9ly |
| RA (ICRS / J2000) | 07h34m36s |
| Declination (ICRS / J2000) | +31d53m18s |
| System structure | Six stars arranged as three binary pairs. |
| Observing interest | A telescope can split the bright visual pair, but cannot show all six individual stars. |
| Visibility from Lewes | Visible at a suitable season and time; maximum altitude about 71 degrees. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate. Magnitude and spectral type describe the bright visual system, rather than all six stars separately.
Sources: SIMBAD: Castor; Torres et al. (2022): Castor orbits and masses
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 2,800ly |
| RA (J2000; approximate centre) | 06h08m54s |
| Declination (J2000; approximate centre) | +24d20m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 63 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 5,000ly |
| RA (J2000; approximate centre) | 07h29m12s |
| Declination (J2000; approximate centre) | +20d55m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 60 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: GEM
An equatorial mounting arrangement with the telescope on one side of the declination axis and a counterweight on the other. Its geometry commonly requires a meridian flip when tracking across the meridian.
ESA's first deep-space mission, famous for its close flyby of Halley's Comet in 1986. Its images revealed the comet's dark, irregular nucleus. It subsequently encountered comet Grigg-Skjellerup in 1992.
| Programme / agency | ESA |
|---|---|
| Key dates | Launched 1985; comet encounters 1986 and 1992 |
| Destination / science location | Comets Halley and Grigg-Skjellerup |
A dense, approximately spherical star cluster, usually containing many thousands to millions of predominantly old stars. Many orbit in the halo around the Milky Way.
Other names and search terms: Go-to, Goto
A computer-controlled system that moves a telescope to selected sky objects after the required setup. Finding an object and tracking it are different functions. GoTo cannot make an obscured or excessively faint target visible.
Other names and search terms: Global Positioning System
A satellite navigation system. A telescope's GPS receiver supplies location and accurate time to its controller. It normally does not tell the telescope where it is pointing or replace star alignment.
Other names and search terms: Green Bank, Green Bank Telescope, GBT
A radio astronomy site in a protected radio-quiet area, known for its large fully steerable Green Bank Telescope.
| Location | Green Bank, West Virginia, USA |
|---|---|
| Type of site | Radio astronomy research observatory |
| Main instruments or facilities | 100m-class Robert C. Byrd Green Bank Telescope and other radio dishes |
| Observing wavelengths | Radio |
| Scientific or historical importance | Sensitive studies of pulsars, interstellar material, galaxies and other radio sources |
Sources: Green Bank Observatory: telescopes
Other names and search terms: Crane, Gru
Grus is one of the 88 IAU-recognised constellations. Its common English description is: crane.
| Common English name | Crane |
|---|---|
| IAU abbreviation | Gru |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Alnair (Alpha Gruis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Alnair |
| Latin / catalogue designation | Alpha Gruis |
| Apparent magnitude (V) | 1.71 |
| Spectral type | B6V |
| Distance from Earth | About 100ly |
| RA (ICRS / J2000) | 22h08m14s |
| Declination (ICRS / J2000) | -46d57m40s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alnair
| Object type | Spiral galaxy |
|---|---|
| Distance from Earth | About 35 million ly |
| RA (J2000; approximate centre) | 22h57m18s |
| Declination (J2000; approximate centre) | -41d04m14s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 7424; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Dr Helen Sharman
The first British person in space. A Sheffield-born chemist, she flew on Soyuz TM-12 in May 1991 for Project Juno and worked aboard the Soviet Mir space station. Her achievement predates Tim Peake's flight by more than two decades.
| Dates | Born 1963; spaceflight 1991 |
|---|---|
| Background | British; Project Juno |
Other names and search terms: Henrietta Leavitt, Leavitt
An American astronomer who discovered the relationship between the pulsation periods and luminosities of Cepheid variable stars. After calibration, this relationship made Cepheids powerful distance indicators and helped astronomers measure distances beyond the Milky Way.
| Dates | 1868-1921 |
|---|---|
| Background | American astronomer; Harvard College Observatory |
Sources: Official or institutional reference: Henrietta Swan Leavitt
Other names and search terms: Hercules (the hero), Her
Hercules is one of the 88 IAU-recognised constellations. Its common English description is: hercules (the hero).
| Common English name | Hercules (the hero) |
|---|---|
| IAU abbreviation | Her |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Kornephoros (Beta Herculis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Kornephoros |
| Latin / catalogue designation | Beta Herculis |
| Apparent magnitude (V) | 2.77 |
| Spectral type | G7IIIaFe-0.5 |
| Distance from Earth | About 150ly |
| RA (ICRS / J2000) | 16h30m13s |
| Declination (ICRS / J2000) | +21d29m23s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 61 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Kornephoros
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 25,000ly |
| RA (J2000; approximate centre) | 16h41m42s |
| Declination (J2000; approximate centre) | +36d28m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 76 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 27,000ly |
| RA (J2000; approximate centre) | 17h17m06s |
| Declination (J2000; approximate centre) | +43d08m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 82 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Herschel
An ESA infrared observatory that studied cold dust, star-forming regions and the evolution of galaxies. British scientists and institutions made major contributions to its instruments and science.
| Agency or partnership | ESA, with international instrument teams and NASA contributions |
|---|---|
| Science orbit / location | Science orbit around Sun-Earth L2 |
| Main telescope or instruments | 3.5m primary mirror; PACS, SPIRE and HIFI instruments |
| Observing wavelengths | Far-infrared and submillimetre |
| Mission history | Launched in 2009; science observations ended in April 2013 when its helium coolant was exhausted |
| Scientific importance | Investigating cold material and star formation that can be hidden at visible wavelengths |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Sources: NASA: Herschel; ESA: Herschel operations
Other names and search terms: H-R diagram, HR diagram, HR, H-R, Russell-Hertzsprung diagram
A plot comparing stars' intrinsic luminosities (or absolute magnitudes) with effective temperature, colour or spectral type. Hotter stars conventionally lie to the left. Main-sequence stars, giants and white dwarfs occupy different regions. The Sun lies on the main sequence at about 5,772K and one solar luminosity; a star's position is not simply a measure of its age.
An ancient Greek astronomer remembered for careful stellar measurements and discovering the precession of the equinoxes by comparing observations from different eras. His work helped establish quantitative positional astronomy long before telescopes.
| Dates | Approximately 190-120 BCE |
|---|---|
| Background | Greek astronomer |
Other names and search terms: Hipparcos satellite
ESA's pioneering astrometry satellite measured accurate stellar positions, parallaxes and motions from space. Its catalogues remain important references and preceded the much larger Gaia surveys.
| Agency or partnership | ESA |
|---|---|
| Science orbit / location | Highly elliptical Earth orbit after a launch-system problem prevented its planned geostationary orbit |
| Main telescope or instruments | Scanning optical astrometry telescope and star-mapping instruments |
| Observing wavelengths | Visible light |
| Mission history | Launched in 1989; mission ended in 1993 |
| Scientific importance | A major improvement in stellar distances and positions; the Hipparcos brightness reference is used elsewhere in this glossary |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Sources: ESA: Hipparcos mission fact sheet; ESA: Hipparcos mission accomplished
The apparent boundary between Earth and sky. In sky charts it usually means the ideal level horizon; buildings, trees and hills can obstruct objects above it.
Other names and search terms: Pendulum clock, Hor
Horologium is one of the 88 IAU-recognised constellations. Its common English description is: pendulum clock.
| Common English name | Pendulum clock |
|---|---|
| IAU abbreviation | Hor |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Alpha Horologii |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Horologii |
| Apparent magnitude (V) | 3.86 |
| Spectral type | K2III |
| Distance from Earth | About 120ly |
| RA (ICRS / J2000) | 04h14m00s |
| Declination (ICRS / J2000) | -42d17m40s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Horologii
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 50,000ly |
| RA (J2000; approximate centre) | 03h12m18s |
| Declination (J2000; approximate centre) | -55d13m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Hubble, HST
A NASA-ESA space observatory that studies the Universe in ultraviolet, visible and near-infrared light. Its sharp images and spectra have helped transform many areas of astronomy.
| Agency or partnership | NASA and ESA |
|---|---|
| Science orbit / location | Low Earth orbit |
| Main telescope or instruments | 2.4m primary mirror; imaging cameras and spectrographs |
| Observing wavelengths | Ultraviolet, visible and near-infrared |
| Mission history | Launched in 1990; upgraded and repaired by Space Shuttle servicing missions |
| Scientific importance | Deep views of galaxies, the expansion of the Universe, stellar evolution and planetary science |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Sources: NASA: Hubble facts
Other names and search terms: Water snake, Hya
Hydra is one of the 88 IAU-recognised constellations. Its common English description is: water snake.
| Common English name | Water snake |
|---|---|
| IAU abbreviation | Hya |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Alphard (Alpha Hydrae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Alphard |
| Latin / catalogue designation | Alpha Hydrae |
| Apparent magnitude (V) | 1.97 |
| Spectral type | K3IIIa |
| Distance from Earth | About 180ly |
| RA (ICRS / J2000) | 09h27m35s |
| Declination (ICRS / J2000) | -08d39m31s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 30 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alphard
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 15 million ly |
| RA (J2000; approximate centre) | 13h37m00s |
| Declination (J2000; approximate centre) | -29d52m00s |
| Visibility from Lewes | Rises, but very low: maximum altitude about 9 degrees; needs a clear southern horizon. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 33,000ly |
| RA (J2000; approximate centre) | 12h39m30s |
| Declination (J2000; approximate centre) | -26d45m00s |
| Visibility from Lewes | Rises, but very low: maximum altitude about 12 degrees; needs a clear southern horizon. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 2,500ly |
| RA (J2000; approximate centre) | 08h13m48s |
| Declination (J2000; approximate centre) | -05d48m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 33 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Lesser water snake, Hyi
Hydrus is one of the 88 IAU-recognised constellations. Its common English description is: lesser water snake.
| Common English name | Lesser water snake |
|---|---|
| IAU abbreviation | Hyi |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Beta Hydri |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Beta Hydri |
| Apparent magnitude (V) | 2.79 |
| Spectral type | G0V |
| Distance from Earth | About 24ly |
| RA (ICRS / J2000) | 00h25m45s |
| Declination (ICRS / J2000) | -77d15m15s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Beta Hydri
| Object type | Young star cluster in the Small Magellanic Cloud |
|---|---|
| Distance from Earth | About 200,000ly |
| RA (J2000; approximate centre) | 01h29m32s |
| Declination (J2000; approximate centre) | -73d33m38s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 602; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
A giant planet such as Uranus or Neptune, richer in heavier substances than Jupiter and Saturn. Materials called ices in planetary science include water, ammonia and methane, but deep interiors are hot and compressed. An ice giant is not a solid frozen world.
Other names and search terms: Icy world
An informal description of a body with a substantial amount of solid ice at or near its surface, such as some outer Solar System moons and dwarf planets. It is not interchangeable with the classification ice giant.
Other names and search terms: Inverted image, Upside down
A change in image orientation. A straight-through astronomical refractor normally shows an upside-down view. This is generally unimportant for astronomy, although it can complicate matching the view to a chart.
Other names and search terms: Noise, Signal-to-noise ratio, SNR
Unwanted variations that obscure detail in a camera image. Combining suitable exposures can improve the signal-to-noise ratio, helping real features stand out from random fluctuations.
How much angle on the sky corresponds to a distance in the image. On a camera it is often expressed in arcseconds per pixel and depends on focal length and pixel size. A longer focal length spreads the same object over a larger image.
Other names and search terms: Indian, Ind
Indus is one of the 88 IAU-recognised constellations. Its common English description is: indian.
| Common English name | Indian |
|---|---|
| IAU abbreviation | Ind |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Alpha Indi |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Indi |
| Apparent magnitude (V) | 3.11 |
| Spectral type | K0III-IV |
| Distance from Earth | About 99ly |
| RA (ICRS / J2000) | 20h37m34s |
| Declination (ICRS / J2000) | -47d17m29s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Indi
| Object type | Galaxy |
|---|---|
| Distance from Earth | About 100 million ly (redshift-based luminosity distance) |
| RA (J2000; approximate centre) | 21h19m00s |
| Declination (J2000; approximate centre) | -48d33m44s |
| Visibility from Lewes | Never visible from Lewes. |
An indicative distance calculated from SIMBAD redshift z=0.007315, using H0=70km/s/Mpc and a flat cosmology with matter density parameter 0.3. This is a luminosity distance, not a direct measurement; local galaxy motions can cause substantial uncertainty, especially at low redshift.
Sources: SIMBAD: NGC 7049
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: IR
Electromagnetic radiation with wavelengths longer than visible red light and shorter than microwaves. Infrared observations help investigate cool objects, dust, star formation and distant galaxies. Some infrared reaches ground-based telescopes, while much is absorbed by the atmosphere.
Combining waves collected at separated telescopes or antennas to measure fine detail. The separation between elements helps determine angular resolution, while their collecting areas and instruments affect sensitivity. A large separation does not make an array identical to a completely filled telescope of that diameter.
Sources: ESO: VLT interferometry
Other names and search terms: IAU
An international organisation of professional astronomers that promotes research, education and cooperation. It has an important role in agreed astronomical nomenclature and definitions, including official constellation boundaries and the naming of celestial objects.
| Area or location | International |
|---|---|
| Role | Professional scientific union and coordinating body |
| Useful for | Astronomical names, conventions, definitions and international cooperation |
Sources: Official organisation information
Other names and search terms: ICRS
The modern reference system used to specify precise celestial positions, with its axes tied to distant extragalactic sources. Its orientation is very close to the conventional J2000 equatorial grid, but the two are not exactly identical. At the rounded precision of these beginner profiles, that small difference is not significant.
Other names and search terms: ISS, Space station
A large, permanently crewed research laboratory assembled in low Earth orbit through international cooperation. Its first module launched in 1998 and continuous human occupation began in November 2000. It supports experiments in microgravity, Earth observation and preparation for longer space missions. From Lewes it can appear as a bright, steady point moving across the sky in a few minutes, reflecting sunlight rather than shining by its own light. Visibility depends on the particular pass and illumination; use a dated prediction rather than fixed star coordinates.
| Programme / agency | NASA, Roscosmos, ESA, JAXA and CSA |
|---|---|
| Key dates | Assembly began 1998; continuous occupation from 2000 |
| Destination / science location | Earth orbit |
| Typical orbit | Roughly 400km altitude; approximately 90 minutes per orbit. Altitude and period vary. |
| Observing | NASA Spot the Station provides location-specific viewing predictions; never point a telescope towards the Sun while searching. |
Sources: Official or institutional reference: International Space Station (ISS); NASA: Spot the Station
The innermost Galilean moon of Jupiter and the most volcanically active world in the Solar System. Gravitational interactions with Jupiter, Europa and Ganymede produce tidal heating that powers its volcanoes.
| Parent planet | Jupiter |
|---|---|
| Order among the Galilean moons | 1 from Jupiter |
| Mean diameter | About 3,643km |
| Orbital distance (semi-major axis) | 421,800km from the planet's centre |
| Orbital period | 1.76914 Earth days |
| Rotation period | 1.76914 Earth days; synchronous with its orbit |
| Composition | Rocky world with an iron-rich core |
Values are approximate reference figures. Orbital distance is measured from the centre of the parent planet, not its cloud tops. The rotation period is relative to distant stars, not the interval between sunrises. These moving Solar System objects have no single fixed RA/Dec position or distance from Earth.
Sources: NASA: Io facts; NASA satellite fact sheet (orbital parameters); JPL: satellite physical parameters (mean radii)
Other names and search terms: ING, William Herschel Telescope, WHT, Isaac Newton Telescope, INT
A group of major optical telescopes on La Palma with strong UK, Dutch and Spanish involvement. Its telescopes support imaging and spectroscopy for stellar, galactic and extragalactic research.
| Location | Roque de los Muchachos Observatory, La Palma, Canary Islands, Spain |
|---|---|
| Type of site | International research telescope group with UK participation |
| Main instruments or facilities | 4.2m William Herschel Telescope and approximately 2.5m Isaac Newton Telescope |
| Observing wavelengths | Optical and, depending on instrument, near-infrared |
| Scientific or historical importance | Wide-field surveys and spectroscopy; the Isaac Newton Telescope originally operated at Herstmonceux before moving to La Palma |
Sources: ING: astronomy and instruments; ING: telescope descriptions
A standard astronomical reference epoch, J2000.0, corresponding to 12:00 Terrestrial Time on 1 January 2000. Star charts often label coordinates as J2000 to identify the reference equator and equinox used. An epoch describes the time of a position, while an equinox describes the orientation of a coordinate grid; they are different concepts. Modern catalogues may instead use the International Celestial Reference System (ICRS).
Other names and search terms: Webb, JWST
A large infrared space observatory studying early galaxies, star formation, planets and planetary atmospheres. Its segmented mirror and sunshield let it collect faint infrared light in a cold environment.
| Agency or partnership | NASA, ESA and the Canadian Space Agency |
|---|---|
| Science orbit / location | Orbit around the Sun-Earth L2 region, roughly 1.5 million km from Earth |
| Main telescope or instruments | Approximately 6.5m primary mirror, made of 18 segments; cameras and spectrographs |
| Observing wavelengths | Mainly near- and mid-infrared, with coverage beginning at visible red wavelengths |
| Mission history | Launched on 25 December 2021 |
| Scientific importance | Observations of early galaxies, dust-obscured star formation and the atmospheres of exoplanets |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Sources: NASA: Webb fact sheet
Other names and search terms: Jodrell Bank, Lovell Telescope
The University of Manchester's radio observatory, famous for the Lovell Telescope and its role in radio astronomy. It also forms part of the UK's e-MERLIN interferometer network.
| Location | Cheshire, England, United Kingdom |
|---|---|
| Type of site | Radio astronomy research site with public engagement facilities |
| Main instruments or facilities | Approximately 76m Lovell radio telescope, Mark II and other antennas |
| Observing wavelengths | Radio |
| Scientific or historical importance | Studies of pulsars and other radio sources, and development of radio astronomy |
Founded by Bernard Lovell in 1945. The giant telescope became operational in 1957 and tracked the carrier rocket of Sputnik 1, an important early demonstration of its space-tracking capability.
Sources: Jodrell Bank: radio telescopes; University of Manchester: Jodrell Bank milestones
Other names and search terms: Kepler
A German astronomer who used Tycho Brahe's observations to formulate three laws of planetary motion. Planets follow ellipses with the Sun at one focus, sweep out equal areas in equal times, and have orbital periods related to the sizes of their orbits.
| Dates | 1571-1630 |
|---|---|
| Background | German astronomer and mathematician |
Sources: Official or institutional reference: Johannes Kepler
Other names and search terms: Flamsteed
The first Astronomer Royal, appointed in 1675, who established systematic observations at Greenwich. His accurate stellar positions supported astronomy and navigation. Flamsteed numbers remain familiar in star designations, usually combined with a constellation's Latin genitive name.
| Dates | 1646-1719 |
|---|---|
| Background | English astronomer |
Sources: Official or institutional reference: John Flamsteed
NASA spacecraft designed to investigate Jupiter's interior, atmosphere, magnetic field and origins from a highly elliptical polar orbit. Its measurements have revealed complex cloud structures and helped constrain the giant planet's internal structure.
| Programme / agency | NASA / JPL |
|---|---|
| Key dates | Launched 2011; entered Jupiter orbit July 2016 |
| Destination / science location | Jupiter |
The largest planet, composed mainly of hydrogen and helium. Its visible cloud layers do not mark a solid surface, and different atmospheric regions rotate at different rates.
| Position from the Sun | 5 of 8 |
|---|---|
| Type | Gas giant |
| Average Sun distance (semi-major axis) | 778,479,000km (5.204AU) |
| Orbital period (sidereal year) | 4,332.589 Earth days (11.86 Earth years) |
| Approximate orbit circumference | 4,890,000,000km |
| Mean diameter | 139,822km |
| Rotation relative to the stars | about 9.925h; prograde |
| Mean solar day | about 9.926h |
| Axial tilt (obliquity) | 3.13 degrees |
| Orbit inclination to the ecliptic | 1.304 degrees |
| Orbital eccentricity | 0.0487 |
| Perihelion (nearest Sun distance) | 740,595,000km |
| Aphelion (farthest Sun distance) | 816,363,000km |
| Known moons | 115 (JPL count checked 25 October 2026) |
Values are approximate. Average distance means semi-major axis; mean diameter is not necessarily the equatorial diameter. Orbit circumference is a calculated ellipse approximation. Orbital elements change with time, and moon counts change as discoveries are recognised. Giant-planet diameters use the conventional atmospheric reference level; rotation is an approximate bulk value, not the rate at every cloud latitude.
Sources: NASA Jupiter fact sheet; JPL recognised planetary satellites
Other names and search terms: Very Large Array, VLA, Jansky VLA
A radio interferometer whose antennas can be moved along three railway arms to change the array's configuration. Signals are combined to form detailed images of radio-emitting objects. The longest separation improves angular resolution; it does not give the same collecting area as one solid dish of that diameter.
| Location | Plains of San Agustin, west of Socorro, New Mexico, USA |
|---|---|
| Main instruments | 27 antennas, each 25m in diameter; maximum separation about 36km |
| Observing wavelengths | Radio |
Sources: Official or institutional reference: Karl G. Jansky Very Large Array
Other names and search terms: K
The SI unit of absolute temperature, written K without a degree sign. Zero kelvin is absolute zero. A change of 1K equals a change of 1 degree Celsius; subtract 273.15 from a kelvin temperature to express it in degrees Celsius.
Other names and search terms: Kepler, K2
A NASA planet-finding mission that monitored stellar brightness to detect transits of exoplanets. Its results showed that planets are common in the Milky Way.
| Agency or partnership | NASA |
|---|---|
| Science orbit / location | Earth-trailing orbit around the Sun |
| Main telescope or instruments | 0.95m clear-aperture Schmidt photometer with a 1.4m primary mirror |
| Observing wavelengths | Broad optical band |
| Mission history | Launched in 2009; later operated as K2; mission ended in 2018 |
| Scientific importance | Discovering large numbers of exoplanets and measuring stellar brightness variations |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Other names and search terms: Keplerian design, Keplerian telescope, Keplerian refractor, Astronomical refractor design
A refracting telescope design with both a converging objective and a converging eyepiece. In the simplest version, both are convex lenses. The objective forms a real, inverted image at its focal plane; the eyepiece sits beyond that image and acts as a magnifier. Viewed straight through, the image is upside down, which is normally unimportant for astronomy. Compared with the Galilean arrangement, the design generally offers a wider, more practical field of view and is the basis of most modern visual astronomical refractors. Modern objectives and eyepieces usually contain several lens elements: it is their overall converging action that matters, rather than every individual lens being convex. A diagonal or image-erecting system can change the final orientation.
| Objective | Converging (positive optical power); convex in the simplest two-lens design. |
|---|---|
| Eyepiece | Converging (positive optical power); convex in the simplest design. |
| Eyepiece position | Beyond the real image formed at the objective's focal plane. |
| Straight-through view | Inverted; generally a wider field than the Galilean arrangement. |
Sources: Museo Galileo: Galilean and Keplerian optical arrangements
A public astronomical observatory and educational charity offering guided astronomy experiences under the dark skies of Northumberland.
| Location | Black Fell, Kielder Forest, Northumberland, England, United Kingdom |
|---|---|
| Type of site | Public observing and astronomy education site |
| Main instruments or facilities | Public observing telescopes and educational facilities |
| Observing wavelengths | Mainly optical observing |
| Scientific or historical importance | Accessible astronomy education and experiences within the Northumberland International Dark Sky Park |
Sources: Kielder Observatory: our observatory
Other names and search terms: Lizard, Lac
Lacerta is one of the 88 IAU-recognised constellations. Its common English description is: lizard.
| Common English name | Lizard |
|---|---|
| IAU abbreviation | Lac |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Stellio (Alpha Lacertae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Stellio |
| Latin / catalogue designation | Alpha Lacertae |
| Apparent magnitude (V) | 3.77 |
| Spectral type | A1V |
| Distance from Earth | About 100ly |
| RA (ICRS / J2000) | 22h31m18s |
| Declination (ICRS / J2000) | +50d16m57s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 89 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Lacertae; IAU: newly adopted star names
| Object type | Open star cluster |
|---|---|
| Distance from Earth | About 2,900ly |
| RA (J2000; approximate centre) | 22h15m09s |
| Declination (J2000; approximate centre) | +49d49m48s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 89 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 7243; Cantat-Gaudin et al. (2020), cluster distances
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
One of five locations in an idealised rotating two-body system where a small object can maintain its relative position under the combined effects of gravity and orbital motion. Spacecraft can follow orbits around these regions; the Sun-Earth L2 region is useful for astronomy, but spacecraft there still need orbit corrections.
Sources: ESA: Planck at L2
Other names and search terms: LMC
A nearby dwarf galaxy associated with the Milky Way. It appears as an extended cloud in the southern sky, with many individual star clusters and nebulae inside it. Its apparent extent crosses constellation boundaries; the coordinates below give a reference centre.
| Distance from Earth | About 160,000ly |
|---|---|
| RA (ICRS / J2000; approximate centre) | 05h23m35s |
| Declination (ICRS / J2000; approximate centre) | -69d45m22s |
| Visibility from Lewes | Never visible from Lewes; a southern-sky target. |
Distance is approximate. A large galaxy does not have one sharply defined observational centre, so catalogue reference positions can differ.
Sources: NASA: Magellanic Cloud distance; SIMBAD: Large Magellanic Cloud
Angular distance north or south of Earth's equator. An equatorial mount's polar-axis elevation is set to match the observing latitude; at Lewes this is approximately 51 degrees.
Other names and search terms: Lion, Leo
Leo is one of the 88 IAU-recognised constellations. Its common English description is: lion.
| Common English name | Lion |
|---|---|
| IAU abbreviation | Leo |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Regulus (Alpha Leonis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Regulus |
| Latin / catalogue designation | Alpha Leonis |
| Apparent magnitude (V) | 1.40 |
| Spectral type | B8IVn |
| Distance from Earth | About 79ly |
| RA (ICRS / J2000) | 10h08m22s |
| Declination (ICRS / J2000) | +11d58m02s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 51 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Regulus
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Algieba |
| Latin / catalogue designation | Gamma Leonis |
| System or component described | Brighter component of the Algieba binary |
| Apparent magnitude (V) | 2.23 (brighter component) |
| Spectral type | K1-IIIFe-1 |
| Distance from Earth | About 130ly (adopted system distance) |
| RA (ICRS / J2000) | 10h19m58s |
| Declination (ICRS / J2000) | +19d50m29s |
| System structure | A physical binary with two giant stars. |
| Observing interest | A close golden pair; good seeing and adequate magnification help separate the two points. |
| Visibility from Lewes | Visible at a suitable season and time; maximum altitude about 59 degrees. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
The magnitude, spectral type and position describe the brighter component. The distance uses the system parallax in SIMBAD. Positions are rounded J2000 references; relative separation changes over the orbit.
Sources: SIMBAD: Algieba primary; SIMBAD: Algieba system parallax
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 35 million ly |
| RA (J2000; approximate centre) | 11h18m54s |
| Declination (J2000; approximate centre) | +13d05m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 52 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 35 million ly |
| RA (J2000; approximate centre) | 11h20m12s |
| Declination (J2000; approximate centre) | +12d59m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 52 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Lesser lion, LMi
Leo Minor is one of the 88 IAU-recognised constellations. Its common English description is: lesser lion.
| Common English name | Lesser lion |
|---|---|
| IAU abbreviation | LMi |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Praecipua (46 Leonis Minoris) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Praecipua |
| Latin / catalogue designation | 46 Leonis Minoris |
| Apparent magnitude (V) | 3.83 |
| Spectral type | K0+III-IV |
| Distance from Earth | About 99ly |
| RA (ICRS / J2000) | 10h53m19s |
| Declination (ICRS / J2000) | +34d12m54s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 73 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Praecipua
| Object type | Spiral galaxy |
|---|---|
| Distance from Earth | About 20 million ly |
| RA (J2000; approximate centre) | 10h43m31s |
| Declination (J2000; approximate centre) | +24d55m20s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 64 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 3344; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Hare, Lep
Lepus is one of the 88 IAU-recognised constellations. Its common English description is: hare.
| Common English name | Hare |
|---|---|
| IAU abbreviation | Lep |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Arneb (Alpha Leporis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Arneb |
| Latin / catalogue designation | Alpha Leporis |
| Apparent magnitude (V) | 2.57 |
| Spectral type | F0Ib |
| Distance from Earth | About 2,200ly |
| RA (ICRS / J2000) | 05h32m44s |
| Declination (ICRS / J2000) | -17d49m20s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 21 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Arneb
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 41,000ly |
| RA (J2000; approximate centre) | 05h24m30s |
| Declination (J2000; approximate centre) | -24d33m00s |
| Visibility from Lewes | Rises, but very low: maximum altitude about 15 degrees; needs a clear southern horizon. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: LAS
A local astronomical society based in Lewes, East Sussex. LAS brings people together through astronomy talks, observing, education and public outreach. The society welcomes beginners and encourages members to learn and share their interest in the night sky.
| Area or location | Lewes and surrounding communities, East Sussex, England |
|---|---|
| Role | Local astronomical society |
| Useful for | Local astronomy, practical learning, talks and outreach |
Sources: Official organisation information
Other names and search terms: Scales, Lib
Libra is one of the 88 IAU-recognised constellations. Its common English description is: scales.
| Common English name | Scales |
|---|---|
| IAU abbreviation | Lib |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Zubeneschamali (Beta Librae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Zubeneschamali |
| Latin / catalogue designation | Beta Librae |
| Apparent magnitude (V) | 2.62 |
| Spectral type | B8Vn |
| Distance from Earth | About 190ly |
| RA (ICRS / J2000) | 15h17m00s |
| Declination (ICRS / J2000) | -09d22m58s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 30 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Zubeneschamali
| Object type | Globular star cluster |
|---|---|
| Distance from Earth | About 41,000ly |
| RA (J2000; approximate centre) | 15h17m24s |
| Declination (J2000; approximate centre) | -21d00m36s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 18 degrees. |
Approximate distance from the Harris globular-cluster catalogue (1997 edition); later determinations may differ.
Sources: SIMBAD: NGC 5897; Harris (1996, 1997 catalogue edition)
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Artificial light that brightens the night sky or interferes with observing. A brighter background makes faint galaxies and nebulae harder to distinguish. It is different from atmospheric seeing.
Other names and search terms: Light collecting area, Light gathering power
The area of the aperture that collects light. For ideal unobstructed circular apertures, light-gathering area increases with the square of diameter: doubling diameter gives four times the area. Obstructions and transmission losses also matter.
Other names and search terms: ly, Light year, Light years
The distance light travels through a vacuum in one Julian year: about 9.46 trillion kilometres. It is a unit of distance, not time. A star 100ly away is seen by light that has travelled for about 100 years. Distances in these profiles are approximate, not exact measurements.
A location's angular position east or west of the Prime Meridian, normally stated from 0 to 180 degrees east or west. Lines of equal longitude run between the geographical poles. Longitude helps determine the orientation of your local celestial meridian; latitude measures how far north or south you are.
Sources: Royal Museums Greenwich: longitude
Other names and search terms: Solar luminosity
The total energy an object emits per second, often measured in watts or relative to the Sun. It is intrinsic output, unlike apparent brightness, which also depends on distance and any intervening absorption.
Other names and search terms: Wolf, Lup
Lupus is one of the 88 IAU-recognised constellations. Its common English description is: wolf.
| Common English name | Wolf |
|---|---|
| IAU abbreviation | Lup |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Uridim (Alpha Lupi) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Uridim |
| Latin / catalogue designation | Alpha Lupi |
| Apparent magnitude (V) | 2.29 |
| Spectral type | B1.5III |
| Distance from Earth | About 460ly |
| RA (ICRS / J2000) | 14h41m56s |
| Declination (ICRS / J2000) | -47d23m18s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
| Object type | Globular star cluster |
|---|---|
| Distance from Earth | About 34,000ly |
| RA (J2000; approximate centre) | 15h46m03s |
| Declination (J2000; approximate centre) | -37d47m11s |
| Visibility from Lewes | At most 1.3 degrees above the horizon: exceptionally low and generally impractical. |
Approximate distance from the Harris globular-cluster catalogue (1997 edition); later determinations may differ.
Sources: SIMBAD: NGC 5986; Harris (1996, 1997 catalogue edition)
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Lynx, Lyn
Lynx is one of the 88 IAU-recognised constellations. Its common English description is: lynx.
| Common English name | Lynx |
|---|---|
| IAU abbreviation | Lyn |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Alpha Lyncis |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Lyncis |
| Apparent magnitude (V) | 3.14 |
| Spectral type | K6III |
| Distance from Earth | About 220ly |
| RA (ICRS / J2000) | 09h21m03s |
| Declination (ICRS / J2000) | +34d23m33s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 74 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Lyncis
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 300,000ly |
| RA (J2000; approximate centre) | 07h38m06s |
| Declination (J2000; approximate centre) | +38d53m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 78 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Lyre, Lyr
Lyra is one of the 88 IAU-recognised constellations. Its common English description is: lyre.
| Common English name | Lyre |
|---|---|
| IAU abbreviation | Lyr |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Vega (Alpha Lyrae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Vega |
| Latin / catalogue designation | Alpha Lyrae |
| Apparent magnitude (V) | 0.03 |
| Spectral type | A0V |
| Distance from Earth | About 25ly |
| RA (ICRS / J2000) | 18h36m56s |
| Declination (ICRS / J2000) | +38d47m01s |
| Among the ten brightest night-sky stars? | Yes: reference rank 5 (Sun excluded). |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 78 degrees. |
Distance is a rounded estimate from the catalogue parallax.
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Epsilon1 Lyrae |
| System or component described | Catalogue reference position and light of the named object; unresolved companions may contribute. |
| Apparent magnitude (V) | 4.68 (combined pair; calculated) |
| Spectral type | A3V+F0V |
| Distance from Earth | About 162ly |
| RA (ICRS / J2000) | 18h44m20s |
| Declination (ICRS / J2000) | +39d40m12s |
| System structure | One of the two close binaries that together form the four principal stars of Epsilon Lyrae. |
| Observing interest | Binoculars separate the wide Double Double into two points. Resolving each point into its close pair needs sufficient aperture, magnification and steady seeing. |
| Visibility from Lewes | Circumpolar from Lewes: remains above the horizon throughout the day and night; needs a dark, clear sky to observe. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate. Combined V magnitude is calculated from the two component magnitudes in the Yale Bright Star Catalogue. The two wide subsystems have separate catalogue parallaxes; their rounded distances need not be identical.
Sources: SIMBAD: Epsilon1 Lyrae; Yale Bright Star Catalogue, fifth edition; NASA: the Double Double; Tokovinin (2008): Epsilon Lyrae hierarchy
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Epsilon2 Lyrae |
| System or component described | Catalogue reference position and light of the named object; unresolved companions may contribute. |
| Apparent magnitude (V) | 4.50 (combined pair; calculated) |
| Spectral type | A6Vn+A7Vn |
| Distance from Earth | About 156ly |
| RA (ICRS / J2000) | 18h44m23s |
| Declination (ICRS / J2000) | +39d36m46s |
| System structure | One of the two close binaries that together form the four principal stars of Epsilon Lyrae. |
| Observing interest | Binoculars separate the wide Double Double into two points. Resolving each point into its close pair needs sufficient aperture, magnification and steady seeing. |
| Visibility from Lewes | Circumpolar from Lewes: remains above the horizon throughout the day and night; needs a dark, clear sky to observe. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate. Combined V magnitude is calculated from the two component magnitudes in the Yale Bright Star Catalogue. The two wide subsystems have separate catalogue parallaxes; their rounded distances need not be identical.
Sources: SIMBAD: Epsilon2 Lyrae; Yale Bright Star Catalogue, fifth edition; NASA: the Double Double; Tokovinin (2008): Epsilon Lyrae hierarchy
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 2,000ly |
| RA (J2000; approximate centre) | 18h53m36s |
| Declination (J2000; approximate centre) | +33d02m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 72 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Power, Magnifying power
How much larger an object's angular size appears through a telescope. Divide telescope focal length by eyepiece focal length: 1,000 mm / 25 mm gives 40x. More magnification does not necessarily reveal more detail.
Other names and search terms: Main-sequence star
The band on a Hertzsprung-Russell diagram occupied by stars that generate energy by fusing hydrogen into helium in their cores. The Sun is a main-sequence star. A star does not simply travel along the whole band as it ages.
Other names and search terms: Maksutov, Mak, MCT
A catadioptric design using a thick, curved meniscus corrector and mirrors to provide a compact tube with a long effective focal length. In common versions the secondary is a reflective spot on the corrector; other versions use a separate secondary.
A mount moved by the observer rather than automatically by motors. Movement may use gentle pushes or slow-motion controls. Manual mounts can be alt-azimuth or equatorial.
A rocky planet with a thin atmosphere, a reddish surface and two small moons, Phobos and Deimos. Its solar day is only slightly longer than an Earth day.
| Position from the Sun | 4 of 8 |
|---|---|
| Type | Rocky (terrestrial) planet |
| Average Sun distance (semi-major axis) | 227,956,000km (1.524AU) |
| Orbital period (sidereal year) | 686.980 Earth days (1.88 Earth years) |
| Approximate orbit circumference | 1,430,000,000km |
| Mean diameter | 6,779km |
| Rotation relative to the stars | 24.6229h; prograde |
| Mean solar day | 24.6597h (a Martian sol) |
| Axial tilt (obliquity) | 25.19 degrees |
| Orbit inclination to the ecliptic | 1.848 degrees |
| Orbital eccentricity | 0.0935 |
| Perihelion (nearest Sun distance) | 206,650,000km |
| Aphelion (farthest Sun distance) | 249,261,000km |
| Known moons | 2 (JPL count checked 25 October 2026) |
Values are approximate. Average distance means semi-major axis; mean diameter is not necessarily the equatorial diameter. Orbit circumference is a calculated ellipse approximation. Orbital elements change with time, and moon counts change as discoveries are recognised.
Sources: NASA Mars fact sheet; JPL recognised planetary satellites
Other names and search terms: Volumetric mean diameter
Twice the volumetric mean radius: the diameter of a sphere with the same volume as the body. It can differ from the wider equatorial diameter of a flattened planet. Giant-planet sizes use a conventional level in their atmospheres because they have no ordinary solid surface.
Other names and search terms: MeerKAT telescope
A sensitive South African radio interferometer in the Karoo. Its separated dishes combine signals to investigate galaxies, pulsars and faint radio structures, including those near the centre of the Milky Way.
| Location | Near Carnarvon, Northern Cape, South Africa |
|---|---|
| Main instruments | Original array: 64 dishes, each 13.5m in diameter |
| Observing wavelengths | Radio |
Other names and search terms: Table mountain, Men
Mensa is one of the 88 IAU-recognised constellations. Its common English description is: table mountain.
| Common English name | Table mountain |
|---|---|
| IAU abbreviation | Men |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Hoerikwaggo (Alpha Mensae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Hoerikwaggo |
| Latin / catalogue designation | Alpha Mensae |
| Apparent magnitude (V) | 5.07 |
| Spectral type | G7V |
| Distance from Earth | About 33ly |
| RA (ICRS / J2000) | 06h10m14s |
| Declination (ICRS / J2000) | -74d45m11s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Mensae; IAU: newly adopted star names
| Object type | Star cluster in the Large Magellanic Cloud |
|---|---|
| Distance from Earth | About 160,000ly (approximate host-galaxy distance) |
| RA (J2000; approximate centre) | 05h27m17s |
| Declination (J2000; approximate centre) | -70d44m14s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 1987; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
The smallest planet and the closest to the Sun. Its iron-rich interior is large relative to its rocky exterior.
| Position from the Sun | 1 of 8 |
|---|---|
| Type | Rocky (terrestrial) planet |
| Average Sun distance (semi-major axis) | 57,909,000km (0.387AU) |
| Orbital period (sidereal year) | 87.969 Earth days (0.24 Earth years) |
| Approximate orbit circumference | 360,000,000km |
| Mean diameter | 4,879.4km |
| Rotation relative to the stars | 58.65 Earth days; prograde |
| Mean solar day | 175.94 Earth days |
| Axial tilt (obliquity) | 0.034 degrees |
| Orbit inclination to the ecliptic | 7.004 degrees |
| Orbital eccentricity | 0.2056 |
| Perihelion (nearest Sun distance) | 46,000,000km |
| Aphelion (farthest Sun distance) | 69,818,000km |
| Known moons | 0 (JPL count checked 25 October 2026) |
Values are approximate. Average distance means semi-major axis; mean diameter is not necessarily the equatorial diameter. Orbit circumference is a calculated ellipse approximation. Orbital elements change with time, and moon counts change as discoveries are recognised.
Sources: NASA Mercury fact sheet; JPL recognised planetary satellites
Other names and search terms: Local meridian, Observer meridian, Celestial meridian
Your local celestial meridian is the great circle passing through your zenith and the north and south celestial poles. Its visible part runs from the north horizon, overhead, to the south horizon. It depends on where you observe: it is not automatically the Greenwich meridian. When a telescope needs a meridian flip, it is this local meridian that matters.
| Why Greenwich differs | Greenwich is the chosen zero-longitude reference. Your local meridian passes through your observing position, so it generally lies in a different meridian plane if your longitude differs. |
|---|---|
| Same longitude, different latitude | Observers at the same longitude share a geographical meridian, even if one is much farther north or south. |
| Watching the sky | Earth's rotation carries celestial objects across local meridians. The same star crosses meridians at different longitudes at different times. |
Sources: Royal Museums Greenwich: meridians
A repositioning of a telescope on a suitable equatorial mount as it tracks past the meridian, keeping the tube clear of the mount or tripod. The requirement depends on mount geometry and limits, not simply its type of gearing.
Other names and search terms: Messier, Messier catalog, M objects
A catalogue of 110 nebulae, star clusters and galaxies, identified by an M followed by a number. It began as Charles Messier's list of objects that might be confused with comets. Many entries are popular observing targets, although their visibility depends on latitude, sky conditions and equipment.
Sources: NASA: Hubble Messier catalogue
Other names and search terms: Mike Foale, C. Michael Foale
A British-American NASA astronaut born in Louth, Lincolnshire. He flew on Space Shuttle missions, worked aboard Mir during its 1997 collision emergency, helped service Hubble and commanded ISS Expedition 8. His career links British scientific training with the American and Russian human-spaceflight programmes.
| Dates | Born 1957 |
|---|---|
| Background | British-American; NASA |
Other names and search terms: Microscope, Mic
Microscopium is one of the 88 IAU-recognised constellations. Its common English description is: microscope.
| Common English name | Microscope |
|---|---|
| IAU abbreviation | Mic |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Gamma Microscopii |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Gamma Microscopii |
| Apparent magnitude (V) | 4.65 |
| Spectral type | G8III |
| Distance from Earth | About 250ly |
| RA (ICRS / J2000) | 21h01m17s |
| Declination (ICRS / J2000) | -32d15m28s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Rises, but very low: maximum altitude about 7 degrees; needs a clear southern horizon. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Gamma Microscopii
| Object type | Galaxy |
|---|---|
| Distance from Earth | About 130 million ly (redshift-based luminosity distance) |
| RA (J2000; approximate centre) | 20h34m21s |
| Declination (J2000; approximate centre) | -31d58m51s |
| Visibility from Lewes | Rises, but very low: maximum altitude about 7 degrees; needs a clear southern horizon. |
An indicative distance calculated from SIMBAD redshift z=0.009317, using H0=70km/s/Mpc and a flat cosmology with matter density parameter 0.3. This is a luminosity distance, not a direct measurement; local galaxy motions can cause substantial uncertainty, especially at low redshift.
Sources: SIMBAD: NGC 6925
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
The galaxy containing the Sun and Solar System. The faint band across a dark sky is the combined light of many stars viewed along its disc.
A broad traditional and cataloguing term for a natural Solar System body orbiting the Sun that is not a major planet, moon or comet. It includes asteroids and many bodies beyond Neptune; some objects also have dwarf-planet status. It does not mean a small version of one of the eight planets. The categories overlap historically, so minor planet and asteroid are often used interchangeably.
Sources: JPL: minor planet
Other names and search terms: Mirror image, Reversed image
A view with reversed handedness, like a reflection in a mirror. A normal mirror star diagonal typically leaves this reversal, so it does not provide a fully correct terrestrial view.
Other names and search terms: Unicorn, Mon
Monoceros is one of the 88 IAU-recognised constellations. Its common English description is: unicorn. The combined light of the Beta Monocerotis triple system makes it brighter than any individual component.
| Common English name | Unicorn |
|---|---|
| IAU abbreviation | Mon |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Beta Monocerotis |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Beta Monocerotis |
| Apparent magnitude (V) | 3.74 |
| Spectral type | B4Ve+B2Vn(e)+B3V:nne |
| Distance from Earth | About 680ly |
| RA (ICRS / J2000) | 06h28m49s |
| Declination (ICRS / J2000) | -07d01m59s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 32 degrees. |
| System structure | A visual triple of three hot stars. |
| Observing interest | A particularly rewarding triple for a small telescope; sufficient magnification reveals three points. |
Distance is a rounded estimate from the catalogue parallax. The parallax is relatively uncertain; the distance is especially approximate. Magnitude and spectral type refer to the unresolved multiple system.
Sources: SIMBAD: Beta Monocerotis
| Object type | Reflection Nebula |
|---|---|
| Distance from Earth | 2,500ly |
| RA (J2000; approximate centre) | 06h39m12s |
| Declination (J2000; approximate centre) | +08d44m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 48 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: The Moon, Luna
Earth's rocky natural satellite. It rotates once in the same time that it orbits Earth, so approximately the same hemisphere faces us. Its orbital and rotation periods are about 27.3 days, while its phase cycle and solar day are about 29.5 days.
| Solar System position | Satellite of Earth, the third planet; not a planet |
|---|---|
| Type | Rocky natural satellite |
| Average distance from Earth | 384,400km (centre to centre) |
| Average distance from the Sun | About 149,600,000km with Earth; varies during both orbits |
| Orbital period around Earth | 27.3217 Earth days (sidereal) |
| Approximate Earth-orbit circumference | 2,410,000km |
| Mean diameter | 3,474.8km |
| Rotation relative to the stars | 27.3217 Earth days; synchronous |
| Mean solar day / phase cycle | 29.53 Earth days |
| Axial tilt to its orbital normal | 6.68 degrees |
| Orbit inclination to the ecliptic | 5.145 degrees |
| Orbital eccentricity around Earth | 0.0549 |
| Representative perigee (Earth distance) | 363,300km |
| Representative apogee (Earth distance) | 405,500km |
| Known natural satellites of its own | 0 |
Distances and orbital elements are approximate and variable. Lunar tilt here is measured relative to its own orbital plane; it is not the tilt relative to the ecliptic. The lunar solar day is the average interval from one local noon to the next.
Sources: NASA Moon fact sheet
Other names and search terms: Lunar phase
The changing fraction of the Moon's sunlit half visible from Earth. It results from the relative positions of the Sun, Earth and Moon, not Earth's shadow except during a lunar eclipse.
The support that holds the telescope tube and allows controlled pointing and, where provided, tracking. A tripod or base supports the mount itself. Stability is important, particularly at high magnification.
Other names and search terms: Mount Wilson, Hooker Telescope, 100-inch Telescope
A historic observatory whose large telescopes helped establish the scale of the Universe and the nature of galaxies. It is closely associated with Edwin Hubble's work.
| Location | Mount Wilson, San Gabriel Mountains, near Los Angeles, California, USA |
|---|---|
| Type of site | Historic optical observatory |
| Main instruments or facilities | 100-inch (approximately 2.54m) Hooker reflector and other instruments |
| Observing wavelengths | Primarily visible light |
| Scientific or historical importance | Observations central to the development of the extragalactic distance scale and evidence for cosmic expansion |
Sources: Mount Wilson: Hooker Telescope
Other names and search terms: MRAO, Lords Bridge Observatory, Cambridge radio observatory
The University of Cambridge's radio astronomy observatory at Lord's Bridge. It is an important site in the history of aperture synthesis and pulsar research, and hosts radio interferometry experiments.
| Location | Lord's Bridge near Harlton, south-west of Cambridge, England, United Kingdom |
|---|---|
| Type of site | University radio astronomy research site |
| Main instruments or facilities | Historic radio arrays and the Arcminute Microkelvin Imager (AMI) |
| Observing wavelengths | Radio |
| Scientific or historical importance | The first pulsars were identified in observations here in 1967; the site helped develop aperture-synthesis imaging |
Other names and search terms: Multiple stars, Triple star, Quadruple star, Sextuple star
A gravitationally associated system containing three or more stars. The stars are often arranged hierarchically: a close pair may have a more distant companion, or two binary pairs may orbit one another. Triple, quadruple and sextuple mean systems with three, four and six stars respectively. A small telescope may show only some of the components.
Other names and search terms: Fly, Mus
Musca is one of the 88 IAU-recognised constellations. Its common English description is: fly.
| Common English name | Fly |
|---|---|
| IAU abbreviation | Mus |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Alpha Muscae |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Muscae |
| Apparent magnitude (V) | 2.65 |
| Spectral type | B2IV |
| Distance from Earth | About 320ly |
| RA (ICRS / J2000) | 12h37m11s |
| Declination (ICRS / J2000) | -69d08m08s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Muscae
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 22,000ly |
| RA (J2000; approximate centre) | 12h59m36s |
| Declination (J2000; approximate centre) | -70d53m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 19,000ly |
| RA (J2000; approximate centre) | 12h25m48s |
| Declination (J2000; approximate centre) | -72d40m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: National Aeronautics and Space Administration
The United States civil space and aeronautics organisation. NASA conducts space missions, Earth and planetary science, astronomy and aeronautics research, and provides extensive public education resources. Its name expands to National Aeronautics and Space Administration.
| Area or location | United States; international scientific collaborations |
|---|---|
| Role | Government space and aeronautics organisation |
| Useful for | Mission information, images, scientific archives and explanations of astronomy |
Sources: Official organisation information
Other names and search terms: Moons, Satellite
A naturally occurring body orbiting a planet or another larger body, commonly called a moon. The Moon is Earth's natural satellite. Counts can change when discoveries are confirmed or recognised; they do not include artificial spacecraft.
Other names and search terms: Nebulae
A cloud of gas or dust in space. Some glow, some reflect starlight and others block background light. Nebulae vary greatly in size and brightness; faint ones often need dark skies.
Commander of Apollo 11 and the first person to step onto the Moon, in July 1969. Buzz Aldrin joined him on the surface while Michael Collins remained in lunar orbit. Armstrong had previously commanded Gemini 8.
| Dates | 1930-2012; Apollo 11 in 1969 |
|---|---|
| Background | American; NASA |
Sources: Official or institutional reference: Neil Armstrong
The outermost of the eight planets. Like Uranus, it is an ice giant with a gaseous outer atmosphere and a hot, dense interior rather than an accessible icy surface.
| Position from the Sun | 8 of 8 |
|---|---|
| Type | Ice giant |
| Average Sun distance (semi-major axis) | 4,514,953,000km (30.181AU) |
| Orbital period (sidereal year) | 60,189.018 Earth days (164.79 Earth years) |
| Approximate orbit circumference | 28,400,000,000km |
| Mean diameter | 49,244km |
| Rotation relative to the stars | about 16.11h; prograde |
| Mean solar day | about 16.11h |
| Axial tilt (obliquity) | 28.32 degrees |
| Orbit inclination to the ecliptic | 1.77 degrees |
| Orbital eccentricity | 0.0097 |
| Perihelion (nearest Sun distance) | 4,471,050,000km |
| Aphelion (farthest Sun distance) | 4,558,857,000km |
| Known moons | 16 (JPL count checked 25 October 2026) |
Values are approximate. Average distance means semi-major axis; mean diameter is not necessarily the equatorial diameter. Orbit circumference is a calculated ellipse approximation. Orbital elements change with time, and moon counts change as discoveries are recognised. Giant-planet diameters use the conventional atmospheric reference level; rotation is an approximate bulk value, not the rate at every cloud latitude.
Sources: NASA Neptune fact sheet; JPL recognised planetary satellites
NASA probe that made the first close flyby of Pluto and its moons in July 2015, revealing a complex, active-looking icy world. It later flew past the Kuiper Belt object Arrokoth on 1 January 2019.
| Programme / agency | NASA; Johns Hopkins APL and Southwest Research Institute |
|---|---|
| Key dates | Launched 2006; Pluto flyby 2015; Arrokoth flyby 2019 |
| Destination / science location | Pluto and the Kuiper Belt |
Other names and search terms: Newtonian
A reflecting telescope with a curved primary mirror at the rear and a flat, angled secondary that directs the converging light to an eyepiece on the side of the tube. A Dobsonian is a common mounting choice for this design.
Other names and search terms: Copernicus
A Polish astronomer whose 1543 book set out a mathematical Sun-centred model in which Earth rotates and orbits the Sun. Earlier thinkers had considered a moving Earth, but his model helped transform European astronomy.
| Dates | 1473-1543 |
|---|---|
| Background | Polish astronomer |
Sources: Official or institutional reference: Nicolaus Copernicus
Other names and search terms: Carpenter's square, Nor
Norma is one of the 88 IAU-recognised constellations. Its common English description is: carpenter's square.
| Common English name | Carpenter's square |
|---|---|
| IAU abbreviation | Nor |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Gamma2 Normae |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Gamma2 Normae |
| Apparent magnitude (V) | 4.02 |
| Spectral type | K0III |
| Distance from Earth | About 140ly |
| RA (ICRS / J2000) | 16h19m50s |
| Declination (ICRS / J2000) | -50d09m20s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Gamma2 Normae
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 3,500ly |
| RA (J2000; approximate centre) | 16h18m54s |
| Declination (J2000; approximate centre) | -57d54m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Fusion
A process in which light atomic nuclei combine to form heavier nuclei and release energy. Fusion of hydrogen into helium powers a main-sequence star, including the Sun. It is a nuclear process rather than ordinary chemical burning.
Sources: NASA: star types
Other names and search terms: Objective lens
The main light-collecting optical element that forms the telescope's image: a lens in a refractor or a primary mirror in a reflector. It is different from the eyepiece.
Other names and search terms: Axial tilt, Axial inclination
The angle between a body's rotation axis and the line perpendicular to its orbital plane, also called axial tilt. Zero means an upright axis relative to the orbit. Values above 90 degrees indicate retrograde rotation under the convention used here. Earth's tilt is about 23.44 degrees and drives its seasons.
A site or facility equipped for astronomical observations. It may contain one telescope, several telescopes or an array of antennas. Some observatories concentrate on research; others combine historic instruments, public observing and education.
Sources: ESO: observatories
Other names and search terms: OSC, Observatory Science Centre, The Observatory Science Centre, Herstmonceux Observatory
An interactive science centre and educational charity at the former Royal Greenwich Observatory site in Herstmonceux. It combines hands-on science, schools programmes and astronomy activities with the historic domes and telescopes. The science centre has operated at the site since 1995. LAS committee member Steven Ward was the only volunteer at the first public session held entirely in Dome E. LAS committee members Ian Whiteley and Paul Whitmarsh are currently serving as volunteers at the centre.
| Area or location | Herstmonceux, East Sussex, England |
|---|---|
| Role | Public science centre, museum and historic observatory site |
| Useful for | Science education, historic telescopes and public astronomy activities |
| Astronomical setting | Former Royal Greenwich Observatory site, with historic telescope domes |
| Observing and education | Optical astronomy activities alongside interactive science exhibits |
Sources: Official organisation information
A record of an observing session: date and time, location, target, telescope, eyepiece, magnification, conditions and what was seen. Short notes or sketches help you compare sessions and develop observing skills.
Other names and search terms: Octant, Oct
Octans is one of the 88 IAU-recognised constellations. Its common English description is: octant.
| Common English name | Octant |
|---|---|
| IAU abbreviation | Oct |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Nu Octantis |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Nu Octantis |
| Apparent magnitude (V) | 3.73 |
| Spectral type | K1III |
| Distance from Earth | About 63ly |
| RA (ICRS / J2000) | 21h41m29s |
| Declination (ICRS / J2000) | -77d23m24s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Nu Octantis
| Object type | Galaxy |
|---|---|
| Distance from Earth | About 120 million ly (redshift-based luminosity distance) |
| RA (J2000; approximate centre) | 01h41m38s |
| Declination (J2000; approximate centre) | -89d20m04s |
| Visibility from Lewes | Never visible from Lewes. |
An indicative distance calculated from SIMBAD redshift z=0.008215, using H0=70km/s/Mpc and a flat cosmology with matter density parameter 0.3. This is a luminosity distance, not a direct measurement; local galaxy motions can cause substantial uncertainty, especially at low redshift.
Sources: SIMBAD: NGC 2573
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
A relatively loose group of stars that formed together from the same cloud. Many lie in the disc of the Milky Way. Open clusters may eventually disperse as gravitational interactions separate their members.
Other names and search terms: Serpent bearer, Oph
Ophiuchus is one of the 88 IAU-recognised constellations. Its common English description is: serpent bearer.
| Common English name | Serpent bearer |
|---|---|
| IAU abbreviation | Oph |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Rasalhague (Alpha Ophiuchi) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Rasalhague |
| Latin / catalogue designation | Alpha Ophiuchi |
| Apparent magnitude (V) | 2.07 |
| Spectral type | A5IVnn |
| Distance from Earth | About 49ly |
| RA (ICRS / J2000) | 17h34m56s |
| Declination (ICRS / J2000) | +12d33m36s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 52 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Rasalhague
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 15,000ly |
| RA (J2000; approximate centre) | 16h57m06s |
| Declination (J2000; approximate centre) | -04d06m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 35 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Two stars that appear close together from Earth but are not a gravitationally bound pair. They may lie at different distances. Their appearance can still make an attractive observing target, but apparent proximity alone does not establish a physical connection.
Sources: Bastian and Anton (2018): interpreting an apparent double
Other names and search terms: Transmission
The fraction of incoming light that passes through an optical system to the image or your eye. Lenses, mirrors, coatings and obstructions affect how much useful light reaches you.
Other names and search terms: OTA, Telescope tube
The telescope's main assembly containing the optics and their tube or supporting structure. An OTA is often sold separately from its mount and tripod.
The path of one body under gravity around another body or their shared centre of mass. A simple bound two-body orbit is an ellipse, with a circle as a special case. Real orbits are perturbed by other bodies.
Other names and search terms: Orbit length, Orbital path length
The approximate distance around an orbital ellipse. The body entries use a calculated ellipse circumference based on semi-major axis and eccentricity, rounded to about three significant figures. This is not an exact measured path for a perturbed real orbit.
Other names and search terms: Inclination, Inclination to the ecliptic
The angle between an orbit's plane and a stated reference plane. Planet inclinations here are relative to the ecliptic, so Earth's reference inclination is 0 degrees. This is different from axial tilt.
Other names and search terms: Year, Length of year, Sidereal year, Revolution period
The time needed to complete an orbit. A sidereal period is measured relative to the stars; a planet's sidereal period around the Sun is its sidereal year. A period is a time, whereas orbit circumference is a distance.
Other names and search terms: Hunter, Ori
Orion is one of the 88 IAU-recognised constellations. Its common English description is: hunter.
| Common English name | Hunter |
|---|---|
| IAU abbreviation | Ori |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Rigel (Beta Orionis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Rigel |
| Latin / catalogue designation | Beta Orionis |
| Apparent magnitude (V) | 0.13 |
| Spectral type | B8Ia |
| Distance from Earth | About 860ly |
| RA (ICRS / J2000) | 05h14m32s |
| Declination (ICRS / J2000) | -08d12m06s |
| Among the ten brightest night-sky stars? | Yes: reference rank 7 (Sun excluded). |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 31 degrees. |
Distance is a rounded estimate from the catalogue parallax. The quoted V magnitude is a representative catalogue value, not a live measurement.
| Role | Additional bright variable star; reference rank 10 |
|---|---|
| Common / proper name | Betelgeuse |
| Latin / catalogue designation | Alpha Orionis |
| Apparent magnitude (V) | 0.42 |
| Spectral type | M1-M2Ia-Iab |
| Distance from Earth | About 550ly (uncertain) |
| RA (ICRS / J2000) | 05h55m10s |
| Declination (ICRS / J2000) | +07d24m25s |
| Among the ten brightest night-sky stars? | Yes: reference rank 10 (Sun excluded). |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 47 degrees. |
A model-based estimate from Joyce et al. (2020); other methods give different distances. Its brightness changes substantially, so its rank is not fixed. The quoted V magnitude is a representative catalogue value, not a live measurement.
Sources: SIMBAD: Betelgeuse; ESA Hipparcos brightness reference; Betelgeuse distance: Joyce et al. (2020)
| Object type | Nebula |
|---|---|
| Distance from Earth | 1,500ly |
| RA (J2000; approximate centre) | 05h35m24s |
| Declination (J2000; approximate centre) | -05d27m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 34 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Nebula |
|---|---|
| Distance from Earth | 1,600ly |
| RA (J2000; approximate centre) | 05h35m36s |
| Declination (J2000; approximate centre) | -05d16m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 34 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Reflection Nebula |
|---|---|
| Distance from Earth | 1,600ly |
| RA (J2000; approximate centre) | 05h46m42s |
| Declination (J2000; approximate centre) | +00d03m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 39 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Palomar, Hale Telescope, 200-inch Telescope
A historic and continuing astronomical research observatory associated with Caltech, particularly famous for the Hale Telescope.
| Location | Palomar Mountain, northern San Diego County, California, USA |
|---|---|
| Type of site | Optical and infrared research observatory |
| Main instruments or facilities | 200-inch (approximately 5.1m) Hale reflector, alongside other telescopes |
| Observing wavelengths | Optical and infrared, depending on instrument |
| Scientific or historical importance | A major role in twentieth-century astronomy and continuing studies of stars, planets and galaxies |
Sources: Caltech: Hale Telescope
The apparent shift in the direction of a nearby star as Earth moves around the Sun. Annual stellar parallax is half the full apparent displacement measured six months apart. For a reliable parallax, distance in parsecs is 1 divided by parallax in arcseconds; very uncertain parallaxes need more careful statistical treatment.
Other names and search terms: Very Large Telescope, VLT, VLTI
ESO's major observing site in northern Chile, home to the Very Large Telescope and its interferometer. Its telescopes can work individually or combine light for particular high-resolution observations.
| Location | Cerro Paranal, Atacama Desert, Chile; approximately 2,635m above sea level |
|---|---|
| Type of site | Optical and infrared research observatory |
| Main instruments or facilities | Four 8.2m VLT Unit Telescopes and four 1.8m Auxiliary Telescopes for interferometry |
| Observing wavelengths | Visible and infrared |
| Scientific or historical importance | High-resolution imaging and spectroscopy, including studies of stars, planets and galactic centres |
Sources: ESO: Very Large Telescope; ESO: Paranal site
Other names and search terms: Parkes, Murriyang, The Dish
CSIRO's observatory near Parkes, famous for its large steerable radio dish, Murriyang. It supports research on pulsars and other radio sources and is remembered for relaying television signals during the Apollo 11 Moon landing.
| Location | Near Parkes, New South Wales, Australia |
|---|---|
| Main instruments | 64m Murriyang radio telescope |
| Observing wavelengths | Radio |
Sources: Official or institutional reference: Parkes Observatory (Murriyang)
Other names and search terms: pc, kpc, Mpc
A distance of about 3.26 light-years, defined from an annual parallax of one arcsecond. Astronomers use pc for parsecs, kpc for thousands of parsecs and Mpc for millions of parsecs.
Other names and search terms: Peacock, Pav
Pavo is one of the 88 IAU-recognised constellations. Its common English description is: peacock.
| Common English name | Peacock |
|---|---|
| IAU abbreviation | Pav |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Peacock (Alpha Pavonis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Peacock |
| Latin / catalogue designation | Alpha Pavonis |
| Apparent magnitude (V) | 1.92 |
| Spectral type | B2IV |
| Distance from Earth | About 180ly |
| RA (ICRS / J2000) | 20h25m39s |
| Declination (ICRS / J2000) | -56d44m06s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Peacock
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 13,000ly |
| RA (J2000; approximate centre) | 19h10m54s |
| Declination (J2000; approximate centre) | -59d59m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 30 million ly |
| RA (J2000; approximate centre) | 19h09m48s |
| Declination (J2000; approximate centre) | -63d51m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Load capacity
A manufacturer's stated load limit for a mount. Include the tube, camera and accessories. Ratings are guides rather than guarantees; long tubes and demanding imaging can need greater stability than the quoted weight suggests.
Other names and search terms: Winged horse, Peg
Pegasus is one of the 88 IAU-recognised constellations. Its common English description is: winged horse.
| Common English name | Winged horse |
|---|---|
| IAU abbreviation | Peg |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Enif (Epsilon Pegasi) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Enif |
| Latin / catalogue designation | Epsilon Pegasi |
| Apparent magnitude (V) | 2.39 |
| Spectral type | K2Ib-II |
| Distance from Earth | About 690ly |
| RA (ICRS / J2000) | 21h44m11s |
| Declination (ICRS / J2000) | +09d52m30s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 49 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Enif
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 33,600ly |
| RA (J2000; approximate centre) | 21h30m00s |
| Declination (J2000; approximate centre) | +12d10m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 51 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 45 million ly |
| RA (J2000; approximate centre) | 22h37m06s |
| Declination (J2000; approximate centre) | +34d25m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 74 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
The point in an Earth-centred orbit at which the orbiting body is closest to Earth. The Moon reaches perigee roughly once per orbit, but its distance at perigee varies.
The point in an orbit at which a body is closest to the Sun. It is different from perigee, which refers to an orbit around Earth.
Other names and search terms: Perseus (the hero), Per
Perseus is one of the 88 IAU-recognised constellations. Its common English description is: perseus (the hero).
| Common English name | Perseus (the hero) |
|---|---|
| IAU abbreviation | Per |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Mirfak (Alpha Persei) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Mirfak |
| Latin / catalogue designation | Alpha Persei |
| Apparent magnitude (V) | 1.79 |
| Spectral type | F5Ib |
| Distance from Earth | About 510ly |
| RA (ICRS / J2000) | 03h24m19s |
| Declination (ICRS / J2000) | +49d51m40s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 89 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Mirfak
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 7,500ly |
| RA (J2000; approximate centre) | 02h19m00s |
| Declination (J2000; approximate centre) | +57d09m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 84 degrees. |
One of the two open clusters forming the Double Cluster. The coordinate refers to this cluster, not the midpoint of the pair. The distance is an approximate reference value.
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 7,500ly |
| RA (J2000; approximate centre) | 02h22m24s |
| Declination (J2000; approximate centre) | +57d07m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 84 degrees. |
One of the two open clusters forming the Double Cluster. The coordinate refers to this cluster, not the midpoint of the pair. The distance is an approximate reference value.
| Object type | Elliptical Galaxy |
|---|---|
| Distance from Earth | 230 million ly |
| RA (J2000; approximate centre) | 03h19m48s |
| Declination (J2000; approximate centre) | +41d31m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 81 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Mars 2020, Ingenuity
NASA's Mars 2020 rover, which landed in Jezero Crater in February 2021. It investigates ancient environments, searches for possible signs of past microbial life and collects selected samples for potential future return. It carried Ingenuity, the small experimental helicopter that demonstrated powered flight on another planet.
| Programme / agency | NASA / JPL |
|---|---|
| Key dates | Launched 2020; landed 2021 |
| Destination / science location | Jezero Crater, Mars |
Sources: Official or institutional reference: Perseverance rover
Other names and search terms: Phoenix, Phe
Phoenix is one of the 88 IAU-recognised constellations. Its common English description is: phoenix.
| Common English name | Phoenix |
|---|---|
| IAU abbreviation | Phe |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Ankaa (Alpha Phoenicis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Ankaa |
| Latin / catalogue designation | Alpha Phoenicis |
| Apparent magnitude (V) | 2.38 |
| Spectral type | K0.5IIIb |
| Distance from Earth | About 85ly |
| RA (ICRS / J2000) | 00h26m17s |
| Declination (ICRS / J2000) | -42d18m22s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Ankaa
| Object type | Dwarf galaxy |
|---|---|
| Distance from Earth | About 13 million ly |
| RA (J2000; approximate centre) | 01h35m05s |
| Declination (J2000; approximate centre) | -41d26m10s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 625; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Painter's easel, Pic
Pictor is one of the 88 IAU-recognised constellations. Its common English description is: painter's easel.
| Common English name | Painter's easel |
|---|---|
| IAU abbreviation | Pic |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Alpha Pictoris |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Pictoris |
| Apparent magnitude (V) | 3.23 |
| Spectral type | A8VnkA6 |
| Distance from Earth | About 97ly |
| RA (ICRS / J2000) | 06h48m11s |
| Declination (ICRS / J2000) | -61d56m29s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Pictoris
| Object type | Dwarf galaxy |
|---|---|
| Distance from Earth | About 17 million ly |
| RA (J2000; approximate centre) | 04h54m13s |
| Declination (J2000; approximate centre) | -53d21m39s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 1705; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
A British-born NASA astronaut and climate scientist from Crowborough, East Sussex. He flew on three Space Shuttle missions, contributing to assembly of the ISS. His scientific work investigated Earth's climate and the interactions between vegetation and the atmosphere.
| Dates | 1955-2016 |
|---|---|
| Background | British-American; NASA |
Other names and search terms: Fishes, Psc
Pisces is one of the 88 IAU-recognised constellations. Its common English description is: fishes.
| Common English name | Fishes |
|---|---|
| IAU abbreviation | Psc |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Alpherg (Eta Piscium) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Alpherg |
| Latin / catalogue designation | Eta Piscium |
| Apparent magnitude (V) | 3.62 |
| Spectral type | G7IIIa |
| Distance from Earth | About 370ly |
| RA (ICRS / J2000) | 01h31m29s |
| Declination (ICRS / J2000) | +15d20m45s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 54 degrees. |
Distance is a rounded estimate from the catalogue parallax. The parallax is relatively uncertain; the distance is especially approximate.
Sources: SIMBAD: Alpherg
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 32 million ly |
| RA (J2000; approximate centre) | 01h36m42s |
| Declination (J2000; approximate centre) | +15d47m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 55 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Southern fish, PsA
Piscis Austrinus is one of the 88 IAU-recognised constellations. Its common English description is: southern fish.
| Common English name | Southern fish |
|---|---|
| IAU abbreviation | PsA |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Fomalhaut (Alpha Piscis Austrini) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Fomalhaut |
| Latin / catalogue designation | Alpha Piscis Austrini |
| Apparent magnitude (V) | 1.16 |
| Spectral type | A4V |
| Distance from Earth | About 25ly |
| RA (ICRS / J2000) | 22h57m39s |
| Declination (ICRS / J2000) | -29d37m20s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Rises, but very low: maximum altitude about 10 degrees; needs a clear southern horizon. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Fomalhaut
| Object type | Galaxy |
|---|---|
| Distance from Earth | About 65 million ly (redshift-based luminosity distance) |
| RA (J2000; approximate centre) | 22h35m46s |
| Declination (J2000; approximate centre) | -26d03m02s |
| Visibility from Lewes | Rises, but very low: maximum altitude about 13 degrees; needs a clear southern horizon. |
An indicative distance calculated from SIMBAD redshift z=0.00460701, using H0=70km/s/Mpc and a flat cosmology with matter density parameter 0.3. This is a luminosity distance, not a direct measurement; local galaxy motions can cause substantial uncertainty, especially at low redshift.
Sources: SIMBAD: NGC 7314
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Planck space observatory
An ESA mission that mapped the cosmic microwave background, the faint radiation left from the early Universe. Its measurements strongly constrained the history and contents of the cosmos.
| Agency or partnership | ESA |
|---|---|
| Science orbit / location | Science orbit around Sun-Earth L2 |
| Main telescope or instruments | 1.5m-class telescope with low- and high-frequency detector instruments |
| Observing wavelengths | Microwave and submillimetre |
| Mission history | Launched in 2009; operations ended in 2013 |
| Scientific importance | Precise maps of the cosmic microwave background and estimates of key cosmological properties |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Sources: ESA: Planck operations; ESA: Planck overview
A substantial natural body orbiting a star, without the sustained hydrogen fusion that powers a star. For our Solar System, the IAU definition requires a planet to orbit the Sun, be nearly round through its own gravity, and gravitationally dominate the neighbourhood of its orbit. This does not mean its orbit must be completely empty. Eight Solar System bodies meet these criteria. The term exoplanet is used for a planet outside our Solar System.
Sources: IAU: Solar System planet definition
An expanding shell of gas shed by an ageing low- or intermediate-mass star, illuminated by its hot remnant. Despite the name, it is unrelated to planets: early telescopic views sometimes resembled small planetary discs.
Other names and search terms: Lunar observing
Observing planets or the Moon to examine features such as cloud belts, rings, craters or mountains. Useful high-power views require suitable optics, accurate focus and steady atmospheric conditions.
A chart showing the sky for a particular latitude, date and time. A traditional planisphere uses rotating discs; an electronic version can display the equivalent view on screen.
Setting an equatorial mount's polar axis parallel to Earth's rotation axis. In the northern hemisphere it points close to Polaris. This establishes tracking geometry and is different from finder alignment or GoTo star alignment.
Other names and search terms: Right ascension axis, RA axis
The main tracking axis of an equatorial mount. When polar-aligned, it is parallel to Earth's rotation axis. Turning around it compensates for the sky's apparent daily motion.
Other names and search terms: Pole Star, North Star
Polaris, also called the Pole Star or North Star, lies close to the north celestial pole, the direction in which Earth's rotation axis points. As Earth turns, it appears almost stationary while other stars trace circles around that part of the sky. This makes it useful for finding north and for polar alignment. It is not exactly at the pole and is not the brightest night-sky star. Precession slowly changes which star serves as the Pole Star.
| Common / proper name | Polaris (Pole Star; North Star) |
|---|---|
| Latin / catalogue designation | Alpha Ursae Minoris |
| Apparent magnitude (V) | 2.02 |
| Spectral type | F8Ib |
| Distance from Earth | About 430ly |
| RA (ICRS / J2000) | 02h31m49s |
| Declination (ICRS / J2000) | +89d15m51s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Circumpolar: above the northern horizon throughout the night, at an altitude close to 51 degrees. A clear, dark sky is still needed. |
| System structure | A triple with one close companion and one wider companion. |
| Observing interest | A small telescope can show the wider companion. The close pair is beyond ordinary visual telescopic resolution. |
Distance is a rounded estimate from the catalogue parallax. The quoted V magnitude is a representative catalogue value, not a live measurement.
Sources: SIMBAD: Polaris; NASA: why Polaris is the North Star; NASA: Polaris triple system
A slow change in the direction of a rotation axis. Earth's axis traces an approximately circular path over about 26,000 years, shifting the celestial poles and the equinoxes against the background stars. This is why the First Point of Aries now lies in Pisces and why coordinate catalogues specify a reference frame or equinox.
The main light-collecting mirror in a reflecting telescope. It normally sits at the rear of the tube and brings incoming light towards a focus.
Other names and search terms: Greenwich Meridian, Greenwich meridian line, Zero longitude
The agreed reference meridian for zero degrees of geographical longitude. The historic Greenwich meridian passes through the Airy Transit Circle at the Royal Observatory, Greenwich, and is marked by a line in the courtyard. It was adopted as the international reference in 1884. Other meridians pass through other locations; yours is local to where you observe.
| Earth coordinates versus sky coordinates | Greenwich zero longitude is a geographical reference on Earth. RA 0h is a celestial reference defined by the First Point of Aries; they are different coordinate origins. |
|---|---|
| Modern satellite coordinates | GPS zero longitude lies approximately 102m east of the historic Greenwich line. Modern Earth-centred coordinates differ from the older astronomical coordinates tied to the local direction of gravity. |
The modern 102m offset is a reference-frame detail at Greenwich. The difference between Greenwich and an observer's local meridian is primarily a question of the observer's longitude.
Sources: Royal Museums Greenwich: the Prime Meridian; Malys et al. (2015): the Greenwich reference-frame offset
Other names and search terms: Chris Lintott, Christopher Lintott, Prof Chris Lintott, Galaxy Zoo, Zooniverse
A British astrophysicist, author and broadcaster at the University of Oxford, well known as a presenter of BBC television's The Sky at Night. He helped establish Galaxy Zoo and the Zooniverse citizen-science platform, enabling volunteers to contribute to research by classifying galaxies and other scientific data. His work combines research into galaxies with public participation and astronomy education.
Other names and search terms: Michele Dougherty, Prof Michele Dougherty
A space physicist and planetary scientist appointed Astronomer Royal in July 2025, the first woman to hold the role. Her work on spacecraft magnetic-field measurements includes the Cassini mission: magnetic signatures helped reveal activity at Saturn's moon Enceladus. She has also led the magnetometer investigation for ESA's Juice mission to Jupiter. Her work connects planetary exploration, instrument development and public understanding of science.
Sources: Official reference: Professor Michele Dougherty; Royal Society: planetary missions and discoveries
Other names and search terms: X3, Black Arrow
A British experimental satellite launched from Woomera, Australia, in October 1971 by a Black Arrow rocket. It was the first successful launch of a British satellite by a British rocket, rather than the first British satellite of any kind. Its experiments tested spacecraft technology and measured micrometeoroids.
| Programme / agency | United Kingdom |
|---|---|
| Key dates | Launched 1971 |
| Destination / science location | Earth orbit |
Other names and search terms: Stern, Pup
Puppis is one of the 88 IAU-recognised constellations. Its common English description is: stern.
| Common English name | Stern |
|---|---|
| IAU abbreviation | Pup |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Naos (Zeta Puppis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Naos |
| Latin / catalogue designation | Zeta Puppis |
| Apparent magnitude (V) | 2.25 |
| Spectral type | O4I(n)fp |
| Distance from Earth | About 1,100ly |
| RA (ICRS / J2000) | 08h03m35s |
| Declination (ICRS / J2000) | -40d00m11s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Naos
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 5,400ly |
| RA (J2000; approximate centre) | 07h41m48s |
| Declination (J2000; approximate centre) | -14d49m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 24 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 4,000ly |
| RA (J2000; approximate centre) | 07h52m18s |
| Declination (J2000; approximate centre) | -38d33m00s |
| Visibility from Lewes | At most 0.6 degrees above the horizon: exceptionally low and generally impractical. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Mariner's compass, Pyx
Pyxis is one of the 88 IAU-recognised constellations. Its common English description is: mariner's compass.
| Common English name | Mariner's compass |
|---|---|
| IAU abbreviation | Pyx |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Alpha Pyxidis |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Pyxidis |
| Apparent magnitude (V) | 3.68 |
| Spectral type | B1.5III |
| Distance from Earth | About 790ly |
| RA (ICRS / J2000) | 08h43m36s |
| Declination (ICRS / J2000) | -33d11m11s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Rises, but very low: maximum altitude about 6 degrees; needs a clear southern horizon. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Pyxidis
| Object type | Planetary nebula |
|---|---|
| Distance from Earth | About 10,400ly |
| RA (J2000; approximate centre) | 09h16m11s |
| Declination (J2000; approximate centre) | -36d37m26s |
| Visibility from Lewes | At most 2.5 degrees above the horizon: exceptionally low and generally impractical. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 2818; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Radio observatories directory
Selected famous radio astronomy sites, including UK facilities. Single dishes and interferometer arrays have different strengths. Arecibo is included for its historical importance; its 305m telescope collapsed in 2020.
| Radio observatory | Description / significance |
|---|---|
| Jodrell Bank Observatory | The University of Manchester's radio observatory, famous for the Lovell Telescope and its role in radio astronomy. |
| Mullard Radio Astronomy Observatory | The University of Cambridge's radio astronomy observatory at Lord's Bridge. |
| Green Bank Observatory | A radio astronomy site in a protected radio-quiet area, known for its large fully steerable Green Bank Telescope.. |
| Arecibo Observatory | A celebrated Puerto Rican radio and radar astronomy site, historically dominated by its enormous fixed reflector. |
| Atacama Large Millimeter/submillimeter Array | An international array of antennas that combines signals to investigate cold gas, dust, forming stars and planets, and distant galaxies. |
| Parkes Observatory (Murriyang) | CSIRO's observatory near Parkes, famous for its large steerable radio dish, Murriyang. |
| Karl G. Jansky Very Large Array | A radio interferometer whose antennas can be moved along three railway arms to change the array's configuration. |
| Effelsberg Radio Telescope | A major fully steerable single-dish radio telescope operated by the Max Planck Institute for Radio Astronomy. |
| MeerKAT | A sensitive South African radio interferometer in the Karoo. |
An instrument that detects radio waves from astronomical objects. It may use a steerable dish, a fixed reflector or many antennas working together. The signals are processed electronically rather than viewed through an eyepiece.
Sources: Jodrell Bank: radio telescopes
A guide to the measurements in the 88 constellation entries. The listed star is the usual representative brightest star or unresolved system in visible light. Near ties, variability and combined multiple-star light can affect the choice. Deep-sky objects are selected examples, not a complete inventory.
| Profile field | Explanation / conventions |
|---|---|
| Star names | The same star can have both a common name and a Latin catalogue designation, for example Sirius (Alpha Canis Majoris). Both are shown where a separate common name is listed. |
| Star coordinates | ICRS positions at epoch J2000, rounded to the nearest second of RA time and arcsecond of declination. Proper motion can change positions over the years. |
| Deep-sky coordinates | Approximate J2000 object centres, generally from NGC 2000.0 (RA to 0.1 minute of time and declination to 1 arcminute) or SIMBAD. A large object extends well beyond its centre. |
| RA and declination notation | RA 05h35m17s means 5 hours, 35 minutes and 17 seconds eastwards from the origin. Dec -05d23m means 5 degrees and 23 arcminutes south of the celestial equator. The ASCII letter d means degrees. |
| Distances | Rounded estimates from SIMBAD parallaxes, NASA/ESA/ESO references or cited cluster catalogues. Selected galaxies use explicitly labelled redshift-based luminosity distances. Published values can differ. |
| Brightness | Apparent V magnitude describes brightness from Earth. Multiple systems may be listed by combined light. Catalogue values and variable-star brightnesses can differ. |
| Top-ten reference | The ordering follows the ESA Hipparcos reference list, excluding the Sun and using combined light where stated. It is not a permanent or live ranking. The profile V magnitudes can come from newer/different measurements. |
| Visibility from Lewes | Calculated for latitude 50.87 degrees N with a level, unobstructed horizon, ignoring refraction. Objects south of approximately -39.13 degrees declination never rise. A maximum altitude under 5 degrees is usually impractical. |
| Constellation visibility | All parts rise means each part can rise at a suitable time, not that the whole region is above the horizon simultaneously. Partly visible can still mean its brightest star never rises. |
| Practical observing | Geometric visibility is not a promise of easy observation. Season, darkness, moonlight, local obstructions, surface brightness and equipment all matter. |
Sources: IAU constellations; SIMBAD astronomical database; Yale Bright Star Catalogue, fifth edition; Astropy IAU boundary method (Roman 1987); ESA Hipparcos brightness reference
A relatively small, cool, low-mass main-sequence star. Red dwarfs fuse hydrogen and can live for extremely long periods, but are faint compared with the Sun. Proxima Centauri is the nearest star beyond the Sun and is a red dwarf.
Sources: NASA: Proxima Centauri
A torch with dim red light used to read charts or handle equipment while limiting disruption to dark adaptation. Keep it faint and avoid shining it towards other observers.
Other names and search terms: Reflex finder, Red dot
An aiming device that shows an illuminated mark against your direct view of the sky. Most do not magnify the view. It must be aligned with the main telescope.
A shift of spectral features towards longer wavelengths. For distant galaxies, cosmological redshift is mainly caused by the expansion of space; local motions also contribute. Converting redshift to distance requires an assumed cosmological model. The redshift-based distances in this glossary are explicitly marked and are especially uncertain for nearby galaxies.
A cloud of dust made visible by scattering the light of nearby stars. It reflects starlight rather than producing most of its visible light through glowing ionised gas.
Other names and search terms: Reflecting telescope
A telescope that uses a curved primary mirror to collect and focus light. A Newtonian is a familiar example. Some designs also use correcting lenses.
Other names and search terms: Refracting telescope
A telescope whose main light-collecting objective is a lens. It bends incoming light to form an image, normally examined through an eyepiece at the rear.
Other names and search terms: Resolution
The ability to distinguish closely spaced features or stars as separate. Larger apertures can resolve finer detail, but atmospheric conditions, optical quality and alignment can limit the actual view.
Other names and search terms: Reticle (eyepiece grid), Ret
Reticulum is one of the 88 IAU-recognised constellations. Its common English description is: reticle (eyepiece grid).
| Common English name | Reticle (eyepiece grid) |
|---|---|
| IAU abbreviation | Ret |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Rhombus (Alpha Reticuli) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Rhombus |
| Latin / catalogue designation | Alpha Reticuli |
| Apparent magnitude (V) | 3.36 |
| Spectral type | G8IIIa: |
| Distance from Earth | About 160ly |
| RA (ICRS / J2000) | 04h14m25s |
| Declination (ICRS / J2000) | -62d28m26s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Reticuli; IAU: newly adopted star names
| Object type | Barred spiral galaxy |
|---|---|
| Distance from Earth | About 14 million ly |
| RA (J2000; approximate centre) | 03h18m16s |
| Declination (J2000; approximate centre) | -66d29m54s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 1313; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Retrograde, Prograde rotation
Rotation opposite to the usual direction of planetary orbital motion. Viewed from north of the ecliptic, most planets rotate anticlockwise, while Venus and Uranus rotate clockwise. This concerns their spin; their orbits around the Sun still run in the usual prograde direction.
Other names and search terms: RA
The celestial equivalent of longitude, measured eastwards around the celestial equator from the First Point of Aries. It is normally written in hours, minutes and seconds: 24h covers 360 degrees, so 1h equals 15 degrees and 0h equals 0 degrees. RA minutes and seconds are units of coordinate time, not arcminutes and arcseconds. Together with declination, RA locates an object on the celestial sphere.
Other names and search terms: Dr Rosemary Coogan
A British ESA astronaut and astrophysicist from Belfast, Northern Ireland. Selected in 2022, she completed ESA basic astronaut training in April 2024. Her scientific training includes a doctorate at the University of Sussex. Astronaut certification and a completed spaceflight are distinct achievements.
| Dates | Born 1991; certified 2024 |
|---|---|
| Background | British; European Space Agency |
Sources: Official or institutional reference: Rosemary Coogan
Other names and search terms: Philae, 67P mission
ESA mission that rendezvoused with comet 67P/Churyumov-Gerasimenko in 2014 and followed it around the Sun. Its Philae lander reached the surface in November 2014. Rosetta studied the nucleus, dust and gas, and ended with a controlled descent to the comet in September 2016.
| Programme / agency | ESA with member-state and NASA contributions |
|---|---|
| Key dates | Launched 2004; comet operations 2014-2016 |
| Destination / science location | Comet 67P/Churyumov-Gerasimenko |
Sources: Official or institutional reference: Rosetta and Philae
Other names and search terms: Planetary rover, Mars rover
A mobile robotic vehicle that explores the surface of another world. Cameras and scientific instruments examine different locations; communication delays mean a rover cannot normally be driven from Earth as if it were a live remote-controlled toy.
Other names and search terms: RAS
A UK learned society founded in 1820, promoting astronomy, Solar System science and geophysics. It supports the research community through scientific meetings, publications, education and representation. Its Fellows include professional researchers, students and knowledgeable amateurs. Dr Robert Massey is both Deputy Executive Director of the Royal Astronomical Society and chair on the LAS committee.
| Area or location | Burlington House, London, England; UK and international membership |
|---|---|
| Role | Learned society for astronomy and geophysics |
| Useful for | Research news, public lectures, education and professional astronomy |
Sources: Official organisation information
Other names and search terms: ROE, UK Astronomy Technology Centre, UK ATC
A centre for astronomical research, teaching and instrument development on Blackford Hill. The site includes the UK Astronomy Technology Centre, the University of Edinburgh's Institute for Astronomy and a visitor centre.
| Location | Blackford Hill, Edinburgh, Scotland, United Kingdom |
|---|---|
| Type of site | Research, astronomical technology and education centre |
| Main instruments or facilities | Instrument laboratories and astronomical research facilities; visitor and historic telescope collections |
| Observing wavelengths | Technology for optical, infrared and other astronomical instruments |
| Scientific or historical importance | Design and construction of instruments for major ground-based and space telescopes |
Sources: Royal Observatory Edinburgh: about; UKRI: UK Astronomy Technology Centre
Other names and search terms: ROG, Greenwich Observatory
The historic observatory in Greenwich, London, associated with the Prime Meridian, navigation and timekeeping. Founded in 1675, the site now combines astronomical heritage with public science and education.
| Location | Greenwich, London, England, United Kingdom |
|---|---|
| Type of site | Historic observatory and public astronomy site |
| Main instruments or facilities | Airy Transit Circle; 28-inch (approximately 0.71m) Great Equatorial refractor |
| Observing wavelengths | Primarily optical astronomy and historical positional measurements |
| Scientific or historical importance | Historic longitude and time standards; long programmes of stellar and double-star observations |
Sources: Royal Museums Greenwich: Royal Observatory; RMG: Great Equatorial Telescope
Other names and search terms: Arrow, Sge
Sagitta is one of the 88 IAU-recognised constellations. Its common English description is: arrow.
| Common English name | Arrow |
|---|---|
| IAU abbreviation | Sge |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Gamma Sagittae |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Gamma Sagittae |
| Apparent magnitude (V) | 3.47 |
| Spectral type | M0-III |
| Distance from Earth | About 290ly |
| RA (ICRS / J2000) | 19h58m45s |
| Declination (ICRS / J2000) | +19d29m32s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 59 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Gamma Sagittae
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 13,000ly |
| RA (J2000; approximate centre) | 19h53m48s |
| Declination (J2000; approximate centre) | +18d47m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 58 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Archer, Sgr
Sagittarius is one of the 88 IAU-recognised constellations. Its common English description is: archer.
| Common English name | Archer |
|---|---|
| IAU abbreviation | Sgr |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Kaus Australis (Epsilon Sagittarii) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Kaus Australis |
| Latin / catalogue designation | Epsilon Sagittarii |
| Apparent magnitude (V) | 1.81 |
| Spectral type | B9IVp_lB? |
| Distance from Earth | About 140ly |
| RA (ICRS / J2000) | 18h24m10s |
| Declination (ICRS / J2000) | -34d23m05s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | At most 4.7 degrees above the horizon: exceptionally low and generally impractical. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Kaus Australis
| Object type | Emission Nebula |
|---|---|
| Distance from Earth | 5,200ly |
| RA (J2000; approximate centre) | 18h03m48s |
| Declination (J2000; approximate centre) | -24d23m00s |
| Visibility from Lewes | Rises, but very low: maximum altitude about 15 degrees; needs a clear southern horizon. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: NASA: Messier 8; NGC 2000.0 position catalogue
| Object type | Nebula |
|---|---|
| Distance from Earth | 5,000ly |
| RA (J2000; approximate centre) | 18h02m18s |
| Declination (J2000; approximate centre) | -23d02m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 16 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 10,000ly |
| RA (J2000; approximate centre) | 18h36m24s |
| Declination (J2000; approximate centre) | -23d54m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 15 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Emission Nebula |
|---|---|
| Distance from Earth | 5,500ly |
| RA (J2000; approximate centre) | 18h20m48s |
| Declination (J2000; approximate centre) | -16d11m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 23 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
The first American woman in space, flying aboard Space Shuttle Challenger on STS-7 in June 1983. A physicist, she later became an influential advocate for science education. She followed earlier Soviet women cosmonauts rather than being the first woman in space.
| Dates | 1951-2012; first spaceflight 1983 |
|---|---|
| Background | American; NASA |
Other names and search terms: Satellites and space probes directory
Selected satellites, space stations and robotic explorers. These profiles give mission history and scientific purpose, rather than live positions or operating-status reports. Space telescopes have their own linked directory.
| Spacecraft / mission | Purpose / significance |
|---|---|
| International Space Station (ISS) | A large, permanently crewed research laboratory assembled in low Earth orbit through international cooperation. |
| Sputnik 1 | The first artificial Earth satellite, launched by the Soviet Union on 4 October 1957. |
| Explorer 1 | The first successful United States satellite. |
| Telstar 1 | An early active communications satellite launched in 1962, famous for relaying transatlantic television signals. |
| Prospero | A British experimental satellite launched from Woomera, Australia, in October 1971 by a Black Arrow rocket. |
| Galileo navigation satellites | Europe's civilian global satellite-navigation system. |
| Voyager 1 | NASA probe that flew past Jupiter in 1979 and Saturn in 1980, including a close encounter with Titan. |
| Voyager 2 | NASA probe that visited Jupiter, Saturn, Uranus and Neptune. |
| Cassini-Huygens | A joint mission comprising NASA's Cassini Saturn orbiter and ESA's Huygens Titan lander, with Italian Space Agency participation. |
| New Horizons | NASA probe that made the first close flyby of Pluto and its moons in July 2015, revealing a complex, active-looking icy world. |
| Rosetta and Philae | ESA mission that rendezvoused with comet 67P/Churyumov-Gerasimenko in 2014 and followed it around the Sun. |
| Giotto | ESA's first deep-space mission, famous for its close flyby of Halley's Comet in 1986. |
| Galileo Jupiter probe | NASA mission comprising a Jupiter orbiter and an atmospheric entry probe. |
| Juno | NASA spacecraft designed to investigate Jupiter's interior, atmosphere, magnetic field and origins from a highly elliptical polar orbit. |
| Viking 1 and Viking 2 | Two NASA missions, each with an orbiter and a lander, that reached Mars in 1976. |
| Curiosity rover | NASA's Mars Science Laboratory rover, which landed in Gale Crater in August 2012. |
| Perseverance rover | NASA's Mars 2020 rover, which landed in Jezero Crater in February 2021. |
A hydrogen-and-helium giant surrounded by a prominent ring system. It has no ordinary solid surface, and its bulk rotation period is less precisely established than that of a rocky planet.
| Position from the Sun | 6 of 8 |
|---|---|
| Type | Gas giant |
| Average Sun distance (semi-major axis) | 1,432,041,000km (9.573AU) |
| Orbital period (sidereal year) | 10,755.699 Earth days (29.45 Earth years) |
| Approximate orbit circumference | 8,990,000,000km |
| Mean diameter | 116,464km |
| Rotation relative to the stars | about 10.7h; prograde |
| Mean solar day | about 10.7h |
| Axial tilt (obliquity) | 26.73 degrees |
| Orbit inclination to the ecliptic | 2.486 degrees |
| Orbital eccentricity | 0.0520 |
| Perihelion (nearest Sun distance) | 1,357,554,000km |
| Aphelion (farthest Sun distance) | 1,506,527,000km |
| Known moons | 293 (JPL count checked 25 October 2026) |
Values are approximate. Average distance means semi-major axis; mean diameter is not necessarily the equatorial diameter. Orbit circumference is a calculated ellipse approximation. Orbital elements change with time, and moon counts change as discoveries are recognised. Giant-planet diameters use the conventional atmospheric reference level; rotation is an approximate bulk value, not the rate at every cloud latitude.
Sources: NASA Saturn fact sheet; JPL recognised planetary satellites
Other names and search terms: SCT, Schmidt Cassegrain
A catadioptric telescope using a thin Schmidt corrector plate, a concave primary mirror and a convex secondary mirror. Light returns through a hole in the primary, producing a long effective focal length in a short tube.
Other names and search terms: STFC
A UK research council within UK Research and Innovation. STFC supports astronomy, space science and other areas of physics through research funding, facilities, laboratories, skills and public engagement.
| Area or location | United Kingdom; research facilities and partnerships in the UK and overseas |
|---|---|
| Role | Research council and provider of scientific facilities |
| Useful for | Understanding how UK astronomical research and instrumentation are supported |
Sources: Official organisation information
Other names and search terms: Scorpion, Sco
Scorpius is one of the 88 IAU-recognised constellations. Its common English description is: scorpion.
| Common English name | Scorpion |
|---|---|
| IAU abbreviation | Sco |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Antares (Alpha Scorpii) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Antares |
| Latin / catalogue designation | Alpha Scorpii |
| Apparent magnitude (V) | 0.91 |
| Spectral type | M1.5Iab+B2Vn |
| Distance from Earth | About 550ly |
| RA (ICRS / J2000) | 16h29m24s |
| Declination (ICRS / J2000) | -26d25m55s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Rises, but very low: maximum altitude about 13 degrees; needs a clear southern horizon. |
Distance is a rounded estimate from the catalogue parallax. The parallax is relatively uncertain; the distance is especially approximate. The quoted V magnitude is a representative catalogue value, not a live measurement.
Sources: SIMBAD: Antares
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 5,500ly |
| RA (J2000; approximate centre) | 16h23m36s |
| Declination (J2000; approximate centre) | -26d32m00s |
| Visibility from Lewes | Rises, but very low: maximum altitude about 13 degrees; needs a clear southern horizon. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: NASA: Messier 4; NGC 2000.0 position catalogue
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 980ly |
| RA (J2000; approximate centre) | 17h53m54s |
| Declination (J2000; approximate centre) | -34d49m00s |
| Visibility from Lewes | At most 4.3 degrees above the horizon: exceptionally low and generally impractical. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: NASA: Messier 7; NGC 2000.0 position catalogue
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 4,000ly |
| RA (J2000; approximate centre) | 17h13m42s |
| Declination (J2000; approximate centre) | -37d06m00s |
| Visibility from Lewes | At most 2.0 degrees above the horizon: exceptionally low and generally impractical. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Sculptor, Scl
Sculptor is one of the 88 IAU-recognised constellations. Its common English description is: sculptor.
| Common English name | Sculptor |
|---|---|
| IAU abbreviation | Scl |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Alpha Sculptoris |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Sculptoris |
| Apparent magnitude (V) | 4.27 |
| Spectral type | B7IIIp |
| Distance from Earth | About 710ly |
| RA (ICRS / J2000) | 00h58m36s |
| Declination (ICRS / J2000) | -29d21m27s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Rises, but very low: maximum altitude about 10 degrees; needs a clear southern horizon. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Sculptoris
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 10 million ly |
| RA (J2000; approximate centre) | 00h47m36s |
| Declination (J2000; approximate centre) | -25d17m00s |
| Visibility from Lewes | Rises, but very low: maximum altitude about 14 degrees; needs a clear southern horizon. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | About 6 million ly |
| RA (J2000; approximate centre) | 00h54m54s |
| Declination (J2000; approximate centre) | -37d41m00s |
| Visibility from Lewes | At most 1.4 degrees above the horizon: exceptionally low and generally impractical. |
Approximate distance from ESO. Coordinates identify the galaxy's approximate centre; the galaxy extends well beyond it.
Sources: ESO: NGC 300 distance; NGC 2000.0 position catalogue
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Shield, Sct
Scutum is one of the 88 IAU-recognised constellations. Its common English description is: shield.
| Common English name | Shield |
|---|---|
| IAU abbreviation | Sct |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Alpha Scuti |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Scuti |
| Apparent magnitude (V) | 3.83 |
| Spectral type | K3III |
| Distance from Earth | About 180ly |
| RA (ICRS / J2000) | 18h35m12s |
| Declination (ICRS / J2000) | -08d14m39s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 31 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Scuti
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 6,200ly |
| RA (J2000; approximate centre) | 18h51m06s |
| Declination (J2000; approximate centre) | -06d16m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 33 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
A smaller mirror that redirects light after it reflects from the primary. A Newtonian's secondary is flat; an SCT's is curved and also changes the beam's convergence.
Other names and search terms: Atmospheric seeing
The steadiness of the atmosphere as it affects astronomical images. Turbulence makes fine details shimmer and stars appear unsteady. A cloudless night can still have poor seeing.
Other names and search terms: Semimajor axis, Average orbital distance
Half the longest diameter of an ellipse. For a planet's orbit it is the conventional representative Sun distance often called its average distance. It is not the current distance or exactly the distance averaged over time.
Other names and search terms: Serpent, Ser
Serpens is one of the 88 IAU-recognised constellations. Its common English description is: serpent. It has two separate regions, Serpens Caput (the head) and Serpens Cauda (the tail), but counts as one constellation.
| Common English name | Serpent |
|---|---|
| IAU abbreviation | Ser |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Unukalhai (Alpha Serpentis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Unukalhai |
| Latin / catalogue designation | Alpha Serpentis |
| Apparent magnitude (V) | 2.63 |
| Spectral type | K2IIIbCN1 |
| Distance from Earth | About 74ly |
| RA (ICRS / J2000) | 15h44m16s |
| Declination (ICRS / J2000) | +06d25m32s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 46 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Unukalhai
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 25,000ly |
| RA (J2000; approximate centre) | 15h18m36s |
| Declination (J2000; approximate centre) | +02d05m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 41 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: NASA: Messier 5; NGC 2000.0 position catalogue
| Object type | Emission Nebula |
|---|---|
| Distance from Earth | 7,000ly |
| RA (J2000; approximate centre) | 18h18m48s |
| Declination (J2000; approximate centre) | -13d47m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 25 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Sextant, Sex
Sextans is one of the 88 IAU-recognised constellations. Its common English description is: sextant.
| Common English name | Sextant |
|---|---|
| IAU abbreviation | Sex |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Alpha Sextantis |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Sextantis |
| Apparent magnitude (V) | 4.49 |
| Spectral type | A0III |
| Distance from Earth | About 430ly |
| RA (ICRS / J2000) | 10h07m56s |
| Declination (ICRS / J2000) | -00d22m18s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 39 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Sextantis
| Object type | Lenticular Galaxy |
|---|---|
| Distance from Earth | 32 million ly |
| RA (J2000; approximate centre) | 10h05m12s |
| Declination (J2000; approximate centre) | -07d43m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 31 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Rotation period, Sidereal day
The time a body takes to rotate once relative to distant stars. It differs from a solar day because the body also moves along its orbit. Earth rotates in about 23h56min relative to the stars but has a mean solar day of 24h.
Other names and search terms: Bernard Lovell, Lovell
A British radio astronomer who founded Jodrell Bank Observatory and led development of its giant steerable radio telescope. His work grew from wartime radar experience into studies of meteors and cosmic radio sources. The 76m Lovell Telescope honours him.
| Dates | 1913-2012 |
|---|---|
| Background | British radio astronomer; University of Manchester |
Sources: Official or institutional reference: Sir Bernard Lovell
Other names and search terms: Isaac Newton, Newton
An English mathematician and physicist whose laws of motion and universal gravitation explained planetary orbits. His work in optics included experiments on the spectrum and construction of a practical reflecting telescope. The Newtonian reflector takes its name from him.
| Dates | 1643-1727 (modern calendar) |
|---|---|
| Background | English physicist and mathematician |
Sources: Official or institutional reference: Sir Isaac Newton
Other names and search terms: Martin Ryle, Ryle
A British radio astronomer who pioneered aperture-synthesis techniques, combining observations from separated antennas to make detailed radio images. He shared the 1974 Nobel Prize in Physics with Antony Hewish for pioneering radio astrophysics.
| Dates | 1918-1984 |
|---|---|
| Background | British radio astronomer; born in Brighton |
Sources: Official or institutional reference: Sir Martin Ryle
Other names and search terms: Patrick Moore, Moore, The Sky at Night
A British amateur astronomer, author and broadcaster who inspired generations of observers through BBC television's The Sky at Night, which he began presenting in 1957. He was an accomplished lunar observer and mapper, and an influential advocate for amateur astronomy. He lived in Selsey, West Sussex, and helped make practical observing accessible to a wide public.
| Dates | 1923-2012 |
|---|---|
| Background | British amateur astronomer and science communicator |
Sources: Official or institutional reference: Sir Patrick Moore
Other names and search terms: William Herschel, Herschel
A German-born British astronomer and telescope maker who discovered Uranus in 1781 and infrared radiation in 1800. Working with Caroline Herschel, he surveyed stars, nebulae and clusters using large reflecting telescopes.
| Dates | 1738-1822 |
|---|---|
| Background | German-born British astronomer |
Sources: Official or institutional reference: Sir William Herschel
Other names and search terms: Star chart, Star atlas
A map showing stars and other astronomical objects. Match its date, time and location where relevant, and learn its orientation before using it to find targets.
Controls that make small, precise movements of a mount, often using knobs or flexible cables. A manual alt-azimuth mount usually needs coordinated movement in both axes to follow a star.
Other names and search terms: SMC
A nearby dwarf galaxy associated with the Milky Way. It appears as an extended cloud in the southern sky, with many individual star clusters and nebulae inside it. Its apparent extent crosses constellation boundaries; the coordinates below give a reference centre.
| Distance from Earth | About 200,000ly |
|---|---|
| RA (ICRS / J2000; approximate centre) | 00h52m38s |
| Declination (ICRS / J2000; approximate centre) | -72d48m01s |
| Visibility from Lewes | Never visible from Lewes; a southern-sky target. |
Distance is approximate. A large galaxy does not have one sharply defined observational centre, so catalogue reference positions can differ.
Sources: NASA: Magellanic Cloud distance; SIMBAD: Small Magellanic Cloud
Other names and search terms: Small Solar System bodies, SSSB
The IAU collective category for natural bodies orbiting the Sun other than planets, dwarf planets and satellites. It includes most asteroids, comets and many objects beyond Neptune. It overlaps with the older term minor planet, but the two expressions are not exact synonyms.
Sources: IAU: Solar System body categories
An integrated system combining optics, a camera, a motorised mount and software to locate and image objects. Many are controlled through a phone or tablet and have no eyepiece. Automation does not remove the need for focus, clear skies and a suitable site.
Other names and search terms: SPA
A UK national society helping people enjoy astronomy, particularly newcomers. It provides practical observing guidance, specialist sections, meetings and the magazine Popular Astronomy. It was founded in 1953 as the Junior Astronomical Society.
| Area or location | United Kingdom |
|---|---|
| Role | Amateur astronomy society with a strong beginner focus |
| Useful for | Starting astronomy, observing guidance and sharing observations |
Sources: Official organisation information
Other names and search terms: Length of day, Day
The interval from one local solar noon to the next, usually quoted as a mean value. It depends on rotation and orbital motion. Earth's mean solar day is24h; Venus's is about 116.75 Earth days despite a rotation period of about 243 Earth days.
Other names and search terms: Solar safety
Equipment specifically designed for observing the Sun safely with the instrument concerned. For a conventional telescope, suitable filters normally fit securely over the front aperture; specialised solar telescopes use purpose-designed systems. Never improvise or use an eyepiece solar filter. Follow expert guidance and protect or remove unfiltered finders.
The Sun and the objects gravitationally bound to it, including planets, dwarf planets, moons, asteroids and comets. It is a small part of the Milky Way galaxy.
Other names and search terms: SAGAS
A network linking astronomical societies across southern England. Established in 1973, SAGAS provides a forum for societies to exchange ideas, coordinate activities and share practical experience. Lewes Astronomical Society is one of its member societies.
| Area or location | Southern England |
|---|---|
| Role | Regional network of astronomical societies |
| Useful for | Cooperation between societies, shared experience and regional meetings |
Sources: Official organisation information; SAGAS member societies
Other names and search terms: Robotic probe, Planetary probe
An uncrewed spacecraft sent to investigate space or celestial bodies. It may fly past a target, orbit it, land on it or release a rover or atmospheric probe. Unlike a telescope observing remotely from Earth, it can make measurements close to its target.
An astronomical instrument carried on a spacecraft, observing above Earth's atmosphere. This avoids atmospheric blurring and gives access to wavelengths that the atmosphere absorbs. Different missions use different orbits, wavelengths and detector designs; a space telescope is not necessarily an optical reflector.
Other names and search terms: Spectral class, Stellar classification, G2 V
A classification based on a star's spectrum, closely related to effective temperature. The traditional stellar spectral sequence runs O, B, A, F, G, K, M from hottest to coolest, with numbered subdivisions. The Sun is G2 V; V is its luminosity class, indicating a main-sequence star. Luminosity classes include I (supergiant), II (bright giant), III (giant), IV (subgiant) and V (main sequence). A plus sign can join the types of multiple stars. Suffixes such as e (emission features), p (peculiar spectrum) and n (broadened lines) add detail; a colon marks uncertainty. Wolf-Rayet types, such as WC, form a separate classification.
A binary detected through periodic changes in spectral lines as the stars move towards and away from us in their orbit. The components may be too close together to resolve in an ordinary telescope. Some systems show spectral lines from both stars; others show only the brighter component.
Splitting light or other electromagnetic radiation into its component wavelengths and measuring the resulting spectrum. Spectral features reveal information such as chemical composition, temperature and motion along the line of sight.
Sources: ESA: XMM-Newton instruments
Other names and search terms: Spitzer
A NASA infrared observatory whose observations revealed cold and dusty regions, distant galaxies and properties of planets around other stars. Its archive continues to support research after the mission ended.
| Agency or partnership | NASA |
|---|---|
| Science orbit / location | Earth-trailing orbit around the Sun |
| Main telescope or instruments | 0.85m primary mirror; infrared cameras and spectrograph |
| Observing wavelengths | Infrared; available wavelength bands changed after its coolant was depleted |
| Mission history | Launched in 2003; mission ended on 30 January 2020 |
| Scientific importance | Infrared studies of star formation and galaxies, and measurements of exoplanets |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Sources: NASA/JPL: Spitzer quick facts; NASA: Spitzer mission
Other names and search terms: Terrestrial telescope, Image-erecting optics
A telescope designed for viewing landscapes or wildlife. Extra prisms or lenses normally provide an upright, correctly oriented image. Such image-erecting optics are usually unnecessary for astronomy.
Other names and search terms: Sputnik
The first artificial Earth satellite, launched by the Soviet Union on 4 October 1957. Its radio signals marked the beginning of the Space Age. It re-entered the atmosphere in January 1958.
| Programme / agency | Soviet Union |
|---|---|
| Key dates | Launched 1957; re-entered 1958 |
| Destination / science location | Earth orbit |
Other names and search terms: Image stacking, Live stacking
Aligning and combining multiple images to improve the visibility of real features relative to random noise. Live stacking updates the displayed result as exposures arrive. It cannot reliably restore detail that was never sharply recorded.
A vast, self-gravitating sphere of hot gas, mostly in the plasma state, which generates energy through nuclear fusion for most of its life. A main-sequence star fuses hydrogen into helium in its core. The Sun is our nearest star. Stars emit their own light, whereas the visible light of planets is mainly reflected starlight. White dwarfs are stellar remnants and no longer sustain core fusion.
Sources: NASA: stars and their lives
Other names and search terms: GoTo alignment, Pointing alignment
A procedure that establishes how a computerised telescope is pointing relative to the sky, often by centring known stars. Some systems automate it with a camera. It is different from polar alignment and GPS location.
A group of stars associated through a shared origin or gravitational binding. Open clusters are generally loose groups; globular clusters are dense, roughly spherical systems containing many stars.
Other names and search terms: Diagonal
A mirror or prism accessory that turns the light path, commonly through 90 degrees, for comfortable viewing with a refractor or SCT. It normally adds no magnification by itself, although it can alter a conventional Barlow's factor by adding spacing. A mirror diagonal typically leaves a mirror-reversed view.
Other names and search terms: Bayer designation, Flamsteed designation, Latin star name, Proper star name, Star naming
A star can have a common or proper name, such as Sirius, and a catalogue designation, such as Alpha Canis Majoris. In a Bayer designation, a Greek letter is followed by the possessive (genitive) form of the Latin constellation name. A Flamsteed designation uses a number instead, as in 61 Cygni. These are alternative identifiers, not translations of the proper name. Greek letters are written out here as Alpha, Beta and so on. Not every star has a separate proper name.
Other names and search terms: Star hopping
Finding a target by following recognisable star patterns from a known starting point, comparing the sky or finder view with a chart.
Other names and search terms: Harmonic drive, Strain wave, Harmonic-drive mount
Compact reduction gearing used in some telescope mounts. It can offer high torque and low backlash, but performance depends on the design. Some mounts allow specified loads without counterweights; the gearing does not by itself remove the need for a meridian flip.
Other names and search terms: Subaru
Japan's large optical-infrared telescope on Maunakea. It is especially known for powerful wide-field observations as well as detailed studies using adaptive optics and spectroscopy.
| Location | Near the summit of Maunakea, Hawai'i Island, Hawai'i, USA |
|---|---|
| Type of site | National Astronomical Observatory of Japan research telescope |
| Main instruments or facilities | 8.2m effective-diameter monolithic primary mirror |
| Observing wavelengths | Visible and infrared |
| Scientific or historical importance | Deep, wide-field surveys of galaxies and other objects, and high-resolution astronomical studies |
Sources: NAOJ: Subaru Telescope
Other names and search terms: Sol
The star at the centre of the Solar System. It produces energy mainly by fusing hydrogen into helium in its core. Its spectral classification is G2 V: G2 describes its spectrum and temperature, and luminosity class V identifies a main-sequence star. On the Hertzsprung-Russell diagram it lies on the main sequence.
| Solar System position | Central star; not a numbered planet |
|---|---|
| Type | Main-sequence star; hot plasma, mainly hydrogen and helium |
| Mean Earth-Sun distance | About 149,600,000km (1AU) |
| Mean diameter | 1,391,400km |
| Rotation relative to the stars | About 25-36 Earth days, depending on latitude |
| Adopted rotation at 16 degrees latitude | 25.38 Earth days (609.12h) |
| Apparent rotation viewed from Earth | About 27 Earth days at low solar latitudes |
| Solar equator tilt to the ecliptic | 7.25 degrees |
| Galactic orbital period | About 230 million Earth years around the Milky Way centre |
| Spectral classification | G2 V |
| Effective temperature | 5,772K |
| Luminosity | About 3.828 x 10^26W (one solar luminosity) |
| H-R diagram position | Main sequence |
The Sun has no solid surface and rotates at different rates at different latitudes. Its solar-equator tilt is relative to the ecliptic, not the plane of its Galactic orbit. Planet-style Sun-orbit distance, eccentricity and inclination are not applicable to the Sun itself. A planetary solar day is not applicable to the Sun itself; apparent rotation means the period seen from Earth. Its planets are not counted as moons. Never observe the Sun without appropriate specialist solar equipment and guidance.
Sources: NASA Sun fact sheet; NASA Sun facts; Chandra introduction to the H-R diagram
Other names and search terms: L2, Second Lagrange point
The second Lagrange point of the Sun-Earth system, about 1.5 million km beyond Earth in the direction away from the Sun. Missions such as Webb and Euclid follow orbits around this region rather than sitting motionless at a point. This geometry helps with thermal control and observing.
Sources: NASA: Webb orbit
How much light an extended object delivers per unit of apparent area. Spreading its light over a larger apparent image can make it look dimmer. Aperture, magnification, exit pupil and transmission must be considered together.
Other names and search terms: Bull, Tau
Taurus is one of the 88 IAU-recognised constellations. Its common English description is: bull.
| Common English name | Bull |
|---|---|
| IAU abbreviation | Tau |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Aldebaran (Alpha Tauri) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Aldebaran |
| Latin / catalogue designation | Alpha Tauri |
| Apparent magnitude (V) | 0.86 |
| Spectral type | K5+III |
| Distance from Earth | About 67ly |
| RA (ICRS / J2000) | 04h35m55s |
| Declination (ICRS / J2000) | +16d30m33s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 56 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Aldebaran
| Object type | Open Cluster |
|---|---|
| Distance from Earth | 445ly |
| RA (J2000; approximate centre) | 03h47m00s |
| Declination (J2000; approximate centre) | +24d07m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 63 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Supernova Remnant |
|---|---|
| Distance from Earth | 6,500ly |
| RA (J2000; approximate centre) | 05h34m30s |
| Declination (J2000; approximate centre) | +22d01m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 61 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: NASA: Messier 1; NGC 2000.0 position catalogue
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Space telescopes, Famous observatories, Observatories, Telescope directory, Observatory directory
Selected space telescopes and famous ground-based observatories, with locations, instruments, wavelength coverage and scientific importance. UK research and public astronomy sites are included alongside international facilities. Mirror diameters, clear apertures and antenna sizes describe different instrument designs, so the figures are not all direct measures of equivalent light-gathering power.
| Telescope / observatory | Location / science orbit |
|---|---|
| Hubble Space Telescope | Space telescope: Low Earth orbit |
| James Webb Space Telescope | Space telescope: Orbit around the Sun-Earth L2 region, roughly 1.5 million km from Earth |
| Chandra X-ray Observatory | Space telescope: Highly elliptical Earth orbit |
| XMM-Newton | Space telescope: Highly elliptical Earth orbit |
| Euclid | Space telescope: Sun-Earth L2 region |
| Gaia | Space telescope: Science observations around Sun-Earth L2; later sent into a retirement orbit around the Sun |
| Herschel Space Observatory | Space telescope: Science orbit around Sun-Earth L2 |
| Spitzer Space Telescope | Space telescope: Earth-trailing orbit around the Sun |
| Kepler Space Telescope | Space telescope: Earth-trailing orbit around the Sun |
| TESS | Space telescope: Highly elliptical Earth orbit with a period of about 13.7 days |
| Planck | Space telescope: Science orbit around Sun-Earth L2 |
| Hipparcos | Space telescope: Highly elliptical Earth orbit after a launch-system problem prevented its planned geostationary orbit |
| Fermi Gamma-ray Space Telescope | Space telescope: Low Earth orbit |
| Royal Observatory Greenwich | Greenwich, London, England, United Kingdom |
| Royal Observatory Edinburgh | Blackford Hill, Edinburgh, Scotland, United Kingdom |
| Jodrell Bank Observatory | Cheshire, England, United Kingdom |
| Mullard Radio Astronomy Observatory | Lord's Bridge near Harlton, south-west of Cambridge, England, United Kingdom |
| Armagh Observatory and Planetarium | Armagh, Northern Ireland, United Kingdom |
| Kielder Observatory | Black Fell, Kielder Forest, Northumberland, England, United Kingdom |
| Isaac Newton Group of Telescopes | Roque de los Muchachos Observatory, La Palma, Canary Islands, Spain |
| Paranal Observatory | Cerro Paranal, Atacama Desert, Chile; approximately 2,635m above sea level |
| Atacama Large Millimeter/submillimeter Array | Chajnantor Plateau, Atacama region, Chile; main array approximately 5,000m above sea level |
| W. M. Keck Observatory | Near the summit of Maunakea, Hawai'i Island, Hawai'i, USA |
| Subaru Telescope | Near the summit of Maunakea, Hawai'i Island, Hawai'i, USA |
| Palomar Observatory | Palomar Mountain, northern San Diego County, California, USA |
| Mount Wilson Observatory | Mount Wilson, San Gabriel Mountains, near Los Angeles, California, USA |
| Green Bank Observatory | Green Bank, West Virginia, USA |
| Arecibo Observatory | Near Arecibo, Puerto Rico, USA |
| Vera C. Rubin Observatory | Cerro Pachon, Chile |
| Observatory Science Centre and Museum | Herstmonceux, East Sussex, England |
| Parkes Observatory (Murriyang) | Near Parkes, New South Wales, Australia |
| Karl G. Jansky Very Large Array | Plains of San Agustin, west of Socorro, New Mexico, USA |
| Effelsberg Radio Telescope | Near Bad Munstereifel, North Rhine-Westphalia, Germany |
| MeerKAT | Near Carnarvon, Northern Cape, South Africa |
Other names and search terms: Telescope, Tel
Telescopium is one of the 88 IAU-recognised constellations. Its common English description is: telescope.
| Common English name | Telescope |
|---|---|
| IAU abbreviation | Tel |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Alpha Telescopii |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Alpha Telescopii |
| Apparent magnitude (V) | 3.46 |
| Spectral type | B3IV |
| Distance from Earth | About 280ly |
| RA (ICRS / J2000) | 18h26m58s |
| Declination (ICRS / J2000) | -45d58m06s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Telescopii
| Object type | Globular star cluster |
|---|---|
| Distance from Earth | About 42,000ly |
| RA (J2000; approximate centre) | 18h18m38s |
| Declination (J2000; approximate centre) | -52d12m57s |
| Visibility from Lewes | Never visible from Lewes. |
Approximate distance from the Harris globular-cluster catalogue (1997 edition); later determinations may differ.
Sources: SIMBAD: NGC 6584; Harris (1996, 1997 catalogue edition)
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Telstar
An early active communications satellite launched in 1962, famous for relaying transatlantic television signals. Ground stations including Goonhilly in Cornwall participated. It was not geostationary, so communication was possible only while it was suitably placed above the participating stations.
| Programme / agency | AT&T; launched by NASA |
|---|---|
| Key dates | Launched 1962 |
| Destination / science location | Earth orbit |
Other names and search terms: Rocky planet
A planet with a solid rocky surface and an interior dominated by rock and metal. Mercury, Venus, Earth and Mars are the Solar System's terrestrial planets. Terrestrial does not mean suitable for human life.
Other names and search terms: Transiting Exoplanet Survey Satellite
NASA's Transiting Exoplanet Survey Satellite monitors large areas of the sky to find planets crossing the faces of nearby bright stars. It also records many other changing astronomical sources.
| Agency or partnership | NASA, led scientifically by MIT |
|---|---|
| Science orbit / location | Highly elliptical Earth orbit with a period of about 13.7 days |
| Main telescope or instruments | Four wide-field cameras, each with a 10.5cm entrance pupil |
| Observing wavelengths | Red visible light and near-infrared |
| Mission history | Launched in 2018 |
| Scientific importance | Finding transiting exoplanets suited to further study and measuring variable stars and transient events |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Sources: NASA/HEASARC: TESS telescope information; MIT: TESS spacecraft
Other names and search terms: Synchronous rotation
A state in which a body's rotation and orbital motion have become synchronised through tidal interactions. In the familiar one-to-one case, its rotation period equals its orbital period, keeping approximately the same face towards its companion. Earth's Moon is an example.
Other names and search terms: Major Tim Peake
A British ESA astronaut from Chichester, West Sussex, who travelled to the ISS in December 2015 for the Principia mission. He conducted scientific experiments and a spacewalk before returning in June 2016. He was the first British ESA astronaut to visit the ISS, rather than the first Briton in space.
| Dates | Born 1972; Principia mission 2015-2016 |
|---|---|
| Background | British; European Space Agency |
Saturn's largest moon and the second-largest moon in the Solar System, after Ganymede. Its thick atmosphere is mostly nitrogen, with methane clouds and rain. Surface lakes and seas contain liquid methane and ethane rather than water; a subsurface water ocean is also thought to exist.
| Parent planet | Saturn |
|---|---|
| Mean diameter | About 5,150km |
| Orbital distance (semi-major axis) | 1,221,870km from the planet's centre |
| Orbital period | 15.94542 Earth days |
| Rotation period | 15.94542 Earth days; synchronous with its orbit |
| Composition | Rocky interior beneath water ice, with a thick atmosphere |
Values are approximate reference figures. Orbital distance is measured from the centre of the parent planet, not its cloud tops. The rotation period is relative to distant stars, not the interval between sunrises. These moving Solar System objects have no single fixed RA/Dec position or distance from Earth.
Sources: NASA: Titan facts; NASA satellite fact sheet (orbital parameters); JPL: satellite physical parameters (mean radii)
Other names and search terms: Motorised tracking, Sidereal tracking
Keeping a telescope aimed at an object as Earth's rotation makes the sky appear to move. This can be done manually or by motors. Tracking is different from automatically finding an object with GoTo.
Other names and search terms: Atmospheric transparency
How clearly light passes through the atmosphere. Haze, thin cloud, dust and moisture can reduce it. Transparency is different from seeing, which concerns atmospheric steadiness.
Other names and search terms: Triangle, Tri
Triangulum is one of the 88 IAU-recognised constellations. Its common English description is: triangle.
| Common English name | Triangle |
|---|---|
| IAU abbreviation | Tri |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Alaybasan (Beta Trianguli) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Alaybasan |
| Latin / catalogue designation | Beta Trianguli |
| Apparent magnitude (V) | 3.00 |
| Spectral type | A5III |
| Distance from Earth | About 130ly |
| RA (ICRS / J2000) | 02h09m33s |
| Declination (ICRS / J2000) | +34d59m14s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 74 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Beta Trianguli; IAU: newly adopted star names
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | About 3 million ly |
| RA (J2000; approximate centre) | 01h33m54s |
| Declination (J2000; approximate centre) | +30d39m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 70 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Southern triangle, TrA
Triangulum Australe is one of the 88 IAU-recognised constellations. Its common English description is: southern triangle.
| Common English name | Southern triangle |
|---|---|
| IAU abbreviation | TrA |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Atria (Alpha Trianguli Australis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Atria |
| Latin / catalogue designation | Alpha Trianguli Australis |
| Apparent magnitude (V) | 1.88 |
| Spectral type | K2III_Ba1 |
| Distance from Earth | About 390ly |
| RA (ICRS / J2000) | 16h48m40s |
| Declination (ICRS / J2000) | -69d01m40s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Atria
| Object type | Open star cluster |
|---|---|
| Distance from Earth | About 2,400ly |
| RA (J2000; approximate centre) | 16h03m07s |
| Declination (J2000; approximate centre) | -60d25m48s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 6025; Cantat-Gaudin et al. (2020), cluster distances
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
A three-legged support for a telescope mount. Rigidity, firm ground and secure fittings help reduce vibration. Some telescopes instead use a pier or a broad ground-level base.
Other names and search terms: TFOV
The angular width of the actual patch of sky visible through a telescope and eyepiece. An approximate value is the eyepiece's apparent field divided by magnification; the eyepiece field stop gives a more precise limit.
Other names and search terms: Toucan, Tuc
Tucana is one of the 88 IAU-recognised constellations. Its common English description is: toucan.
| Common English name | Toucan |
|---|---|
| IAU abbreviation | Tuc |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Lang-Exster (Alpha Tucanae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Lang-Exster |
| Latin / catalogue designation | Alpha Tucanae |
| Apparent magnitude (V) | 2.82 |
| Spectral type | K3III |
| Distance from Earth | About 180ly |
| RA (ICRS / J2000) | 22h18m30s |
| Declination (ICRS / J2000) | -60d15m35s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alpha Tucanae; IAU: newly adopted star names
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 27,000ly |
| RA (J2000; approximate centre) | 01h03m12s |
| Declination (J2000; approximate centre) | -70d51m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 16,700ly |
| RA (J2000; approximate centre) | 00h24m06s |
| Declination (J2000; approximate centre) | -72d05m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Tycho
A Danish astronomer who obtained exceptionally precise naked-eye measurements of stars and planets before telescopic astronomy. His planetary observations, particularly of Mars, supplied crucial evidence for Kepler's laws.
| Dates | 1546-1601 |
|---|---|
| Background | Danish astronomer |
Other names and search terms: UKSA
The UK government organisation coordinating national space policy, strategy and programmes with industry, researchers and international partners. Its work includes space science, innovation and the wider use of space technologies.
| Area or location | United Kingdom |
|---|---|
| Role | Government space organisation |
| Useful for | UK space programmes, policy, educational material and international participation |
Sources: Official organisation information
Other names and search terms: UV
Electromagnetic radiation with wavelengths shorter than visible violet light and longer than X-rays. It is useful for studying hot stars and energetic gas. Much astronomical ultraviolet is blocked by Earth's atmosphere, so space telescopes are important.
Sources: NASA: Hubble wavelength coverage
An ice giant with an extreme axial tilt, so it rotates almost on its side. The term ice giant describes its composition and formation; it is not a solid ball of frozen ice.
| Position from the Sun | 7 of 8 |
|---|---|
| Type | Ice giant |
| Average Sun distance (semi-major axis) | 2,867,043,000km (19.165AU) |
| Orbital period (sidereal year) | 30,685.400 Earth days (84.01 Earth years) |
| Approximate orbit circumference | 18,000,000,000km |
| Mean diameter | 50,724km |
| Rotation relative to the stars | about 17.24h; retrograde |
| Mean solar day | about 17.24h |
| Axial tilt (obliquity) | 97.77 degrees |
| Orbit inclination to the ecliptic | 0.77 degrees |
| Orbital eccentricity | 0.0469 |
| Perihelion (nearest Sun distance) | 2,732,696,000km |
| Aphelion (farthest Sun distance) | 3,001,390,000km |
| Known moons | 29 (JPL count checked 25 October 2026) |
Values are approximate. Average distance means semi-major axis; mean diameter is not necessarily the equatorial diameter. Orbit circumference is a calculated ellipse approximation. Orbital elements change with time, and moon counts change as discoveries are recognised. Giant-planet diameters use the conventional atmospheric reference level; rotation is an approximate bulk value, not the rate at every cloud latitude.
Sources: NASA Uranus fact sheet; JPL recognised planetary satellites
Other names and search terms: Great bear, UMa
Ursa Major is one of the 88 IAU-recognised constellations. Its common English description is: great bear. The Plough is an asterism within it, not a separate constellation.
| Common English name | Great bear |
|---|---|
| IAU abbreviation | UMa |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Alioth (Epsilon Ursae Majoris) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Alioth |
| Latin / catalogue designation | Epsilon Ursae Majoris |
| Apparent magnitude (V) | 1.77 |
| Spectral type | A1III-IVpkB9 |
| Distance from Earth | About 83ly |
| RA (ICRS / J2000) | 12h54m02s |
| Declination (ICRS / J2000) | +55d57m35s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 85 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Alioth
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Mizar |
| Latin / catalogue designation | Zeta Ursae Majoris |
| System or component described | Brighter visual subsystem of the Mizar quadruple; companions are not all resolved |
| Apparent magnitude (V) | 2.22 |
| Spectral type | A1.5Vas |
| Distance from Earth | About 81.1ly |
| RA (ICRS / J2000) | 13h23m56s |
| Declination (ICRS / J2000) | +54d55m31s |
| System structure | A quadruple consisting of two close binary pairs; associated with the binary Alcor. |
| Observing interest | A small telescope shows two bright visual points within Mizar. Together with Alcor, the group contains six known stars. |
| Visibility from Lewes | Circumpolar from Lewes: remains above the horizon throughout the day and night; needs a dark, clear sky to observe. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate. The magnitude, spectrum and reference position describe the brighter visual subsystem. Mizar and Alcor are widely regarded as a very wide sextuple, although determining their precise outer orbit is difficult.
Sources: SIMBAD: Mizar; Mamajek et al. (2010): Mizar and Alcor
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Alcor |
| Latin / catalogue designation | 80 Ursae Majoris |
| System or component described | Catalogue reference position and light of the named object; unresolved companions may contribute. |
| Apparent magnitude (V) | 4.01 |
| Spectral type | A5V+M3-4V |
| Distance from Earth | About 81.7ly |
| RA (ICRS / J2000) | 13h25m14s |
| Declination (ICRS / J2000) | +54d59m17s |
| System structure | A binary companion to the Mizar quadruple, making a six-star association. |
| Observing interest | Mizar and Alcor can be separated without optical aid under suitable conditions, or easily in binoculars. Alcor's own faint companion is not a routine small-telescope target. |
| Visibility from Lewes | Circumpolar from Lewes: remains above the horizon throughout the day and night; needs a dark, clear sky to observe. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate.
Sources: SIMBAD: Alcor; Mamajek et al. (2010): Mizar and Alcor
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 11.6 million ly |
| RA (J2000; approximate centre) | 09h55m36s |
| Declination (J2000; approximate centre) | +69d04m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 72 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 12 million ly |
| RA (J2000; approximate centre) | 09h55m48s |
| Declination (J2000; approximate centre) | +69d41m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 71 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 25 million ly |
| RA (J2000; approximate centre) | 14h03m12s |
| Declination (J2000; approximate centre) | +54d21m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 87 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Little bear, UMi
Ursa Minor is one of the 88 IAU-recognised constellations. Its common English description is: little bear.
| Common English name | Little bear |
|---|---|
| IAU abbreviation | UMi |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Polaris (Alpha Ursae Minoris) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Polaris |
| Latin / catalogue designation | Alpha Ursae Minoris |
| Apparent magnitude (V) | 2.02 |
| Spectral type | F8Ib |
| Distance from Earth | About 430ly |
| RA (ICRS / J2000) | 02h31m49s |
| Declination (ICRS / J2000) | +89d15m51s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Circumpolar: above the northern horizon throughout the night, at an altitude close to 51 degrees. A clear, dark sky is still needed. |
| System structure | A triple with one close companion and one wider companion. |
| Observing interest | A small telescope can show the wider companion. The close pair is beyond ordinary visual telescopic resolution. |
Distance is a rounded estimate from the catalogue parallax. The quoted V magnitude is a representative catalogue value, not a live measurement. Polaris is called the Pole Star because it lies close to the direction of Earth's north rotation axis and appears almost stationary as Earth turns.
Sources: SIMBAD: Polaris; NASA: Polaris triple; NASA: the North Star
| Object type | Barred spiral galaxy |
|---|---|
| Distance from Earth | About 60 million ly |
| RA (J2000; approximate centre) | 16h32m39s |
| Declination (J2000; approximate centre) | +78d11m53s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 63 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 6217; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
The first woman in space. She flew aboard Vostok 6 in June 1963, spending almost three days in orbit. Her flight showed that women could undertake the demanding work of orbital space travel.
| Dates | Born 1937; historic flight 1963 |
|---|---|
| Background | Soviet cosmonaut |
Sources: Official or institutional reference: Valentina Tereshkova
Other names and search terms: Sails, Vel
Vela is one of the 88 IAU-recognised constellations. Its common English description is: sails.
| Common English name | Sails |
|---|---|
| IAU abbreviation | Vel |
| Visibility from Lewes (50.87 degrees N) | Partly. Only its northern portion rises; southern stars and objects may never rise. |
| Representative brightest star | Gamma2 Velorum |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Gamma2 Velorum |
| Apparent magnitude (V) | 1.83 |
| Spectral type | WC8+O7.5III-V |
| Distance from Earth | About 1,100ly |
| RA (ICRS / J2000) | 08h09m32s |
| Declination (ICRS / J2000) | -47d20m12s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax. The parallax is relatively uncertain; the distance is especially approximate.
Sources: SIMBAD: Gamma2 Velorum
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 2,000ly |
| RA (J2000; approximate centre) | 10h07m00s |
| Declination (J2000; approximate centre) | -40d26m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Globular Cluster |
|---|---|
| Distance from Earth | 16,000ly |
| RA (J2000; approximate centre) | 10h17m36s |
| Declination (J2000; approximate centre) | -46d25m00s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
A rocky planet with a dense carbon-dioxide atmosphere. It rotates slowly in the retrograde direction, so its solar day is shorter than one rotation relative to the stars.
| Position from the Sun | 2 of 8 |
|---|---|
| Type | Rocky (terrestrial) planet |
| Average Sun distance (semi-major axis) | 108,210,000km (0.723AU) |
| Orbital period (sidereal year) | 224.701 Earth days (0.62 Earth years) |
| Approximate orbit circumference | 680,000,000km |
| Mean diameter | 12,103.6km |
| Rotation relative to the stars | 243.03 Earth days; retrograde |
| Mean solar day | 116.75 Earth days |
| Axial tilt (obliquity) | 177.36 degrees |
| Orbit inclination to the ecliptic | 3.395 degrees |
| Orbital eccentricity | 0.0068 |
| Perihelion (nearest Sun distance) | 107,480,000km |
| Aphelion (farthest Sun distance) | 108,941,000km |
| Known moons | 0 (JPL count checked 25 October 2026) |
Values are approximate. Average distance means semi-major axis; mean diameter is not necessarily the equatorial diameter. Orbit circumference is a calculated ellipse approximation. Orbital elements change with time, and moon counts change as discoveries are recognised.
Sources: NASA Venus fact sheet; JPL recognised planetary satellites
Other names and search terms: Rubin Observatory, Rubin, Simonyi Survey Telescope, LSST, Legacy Survey of Space and Time
An observatory built for repeated wide-field imaging of the southern sky. Its Legacy Survey of Space and Time is designed to record how objects change and move, while mapping vast numbers of stars and galaxies.
| Location | Cerro Pachon, Chile |
|---|---|
| Type of site | Wide-field optical survey observatory |
| Main instruments or facilities | 8.4m-class Simonyi Survey Telescope with a combined primary/tertiary mirror and LSST Camera |
| Observing wavelengths | Optical bands from near-ultraviolet through near-infrared |
| Scientific or historical importance | Repeated imaging for moving Solar System objects, variable and explosive events, and the structure of the Universe |
Sources: Rubin Observatory: about; Rubin Observatory: telescope
Other names and search terms: Viking, Viking landers
Two NASA missions, each with an orbiter and a lander, that reached Mars in 1976. Their landers returned detailed surface images, weather measurements and biological experiments. The experiments did not establish that life existed on Mars.
| Programme / agency | NASA |
|---|---|
| Key dates | Both launched 1975; both landed 1976 |
| Destination / science location | Mars |
Sources: Official or institutional reference: Viking 1 and Viking 2
Other names and search terms: Maiden, Vir
Virgo is one of the 88 IAU-recognised constellations. Its common English description is: maiden.
| Common English name | Maiden |
|---|---|
| IAU abbreviation | Vir |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Spica (Alpha Virginis) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Spica |
| Latin / catalogue designation | Alpha Virginis |
| Apparent magnitude (V) | 0.97 |
| Spectral type | B1V |
| Distance from Earth | About 250ly |
| RA (ICRS / J2000) | 13h25m12s |
| Declination (ICRS / J2000) | -11d09m41s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 28 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Spica
| Role | Selected double or multiple star |
|---|---|
| Common / proper name | Porrima |
| Latin / catalogue designation | Gamma Virginis |
| System or component described | Catalogue reference position and light of the named object; unresolved companions may contribute. |
| Apparent magnitude (V) | 2.74 |
| Spectral type | F1-F2V |
| Distance from Earth | About 39.2ly |
| RA (ICRS / J2000) | 12h41m40s |
| Declination (ICRS / J2000) | -01d26m58s |
| System structure | A physical binary with two similar F-type stars. |
| Observing interest | A fine pair of near-equal stars. Their angular separation changes over the orbit, so check current double-star information before planning an observation. |
| Visibility from Lewes | Visible at a suitable season and time; maximum altitude about 38 degrees. |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
Coordinates are rounded reference positions, not predictions of the current relative positions of the components. Distances and magnitudes are approximate. The quoted V magnitude is the combined light; the spectrum is the catalogue classification of the system.
Sources: SIMBAD: Porrima
| Object type | Elliptical Galaxy |
|---|---|
| Distance from Earth | 54 million ly |
| RA (J2000; approximate centre) | 12h30m48s |
| Declination (J2000; approximate centre) | +12d24m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 52 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
| Object type | Spiral Galaxy |
|---|---|
| Distance from Earth | 28 million ly |
| RA (J2000; approximate centre) | 12h40m00s |
| Declination (J2000; approximate centre) | -11d37m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 28 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
A physical binary whose components can be resolved separately with suitable imaging or a telescope. Observations over time can trace their orbital motion. The broader phrase visual double also includes pairs whose physical association is uncertain.
Other names and search terms: Flying fish, Vol
Volans is one of the 88 IAU-recognised constellations. Its common English description is: flying fish.
| Common English name | Flying fish |
|---|---|
| IAU abbreviation | Vol |
| Visibility from Lewes (50.87 degrees N) | No. Its entire IAU region stays below the horizon from Lewes. |
| Representative brightest star | Beta Volantis |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Beta Volantis |
| Apparent magnitude (V) | 3.76 |
| Spectral type | K2III |
| Distance from Earth | About 110ly |
| RA (ICRS / J2000) | 08h25m44s |
| Declination (ICRS / J2000) | -66d08m13s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax. The quoted V magnitude is a representative catalogue value, not a live measurement.
Sources: SIMBAD: Beta Volantis
| Role | Nearly equal brightest star; catalogue values differ |
|---|---|
| Common / proper name | No separate common name listed here; use the catalogue designation. |
| Latin / catalogue designation | Gamma2 Volantis |
| Apparent magnitude (V) | 3.75 |
| Spectral type | K0III |
| Distance from Earth | About 130ly |
| RA (ICRS / J2000) | 07h08m45s |
| Declination (ICRS / J2000) | -70d29m56s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Never visible from Lewes. |
Distance is a rounded estimate from the catalogue parallax. The quoted V magnitude is a representative catalogue value, not a live measurement.
Sources: SIMBAD: Gamma2 Volantis
| Object type | Distorted spiral galaxy |
|---|---|
| Distance from Earth | About 50 million ly |
| RA (J2000; approximate centre) | 07h36m24s |
| Declination (J2000; approximate centre) | -69d31m51s |
| Visibility from Lewes | Never visible from Lewes. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
Sources: SIMBAD: NGC 2442; Published distance reference
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye. Beta and Gamma2 are very close in brightness, and catalogues differ about their order; both are included.
Sources: IAU: the 88 constellations
Other names and search terms: Voyager I
NASA probe that flew past Jupiter in 1979 and Saturn in 1980, including a close encounter with Titan. In 2012 it crossed the heliopause into interstellar space: beyond the solar-wind bubble, although still far inside the distant region conventionally associated with the Oort Cloud. It carries a Golden Record containing sounds and images of Earth.
| Programme / agency | NASA / JPL |
|---|---|
| Key dates | Launched 1977; heliopause crossing 2012 |
| Destination / science location | Jupiter, Saturn and interstellar space |
Other names and search terms: Voyager II
NASA probe that visited Jupiter, Saturn, Uranus and Neptune. Its 1986 Uranus and 1989 Neptune encounters remain the only spacecraft flybys of those planets. It crossed the heliopause in 2018. Its launch preceded Voyager 1 despite its higher number.
| Programme / agency | NASA / JPL |
|---|---|
| Key dates | Launched 1977; heliopause crossing 2018 |
| Destination / science location | Four giant planets and interstellar space |
Other names and search terms: Little fox, Vul
Vulpecula is one of the 88 IAU-recognised constellations. Its common English description is: little fox.
| Common English name | Little fox |
|---|---|
| IAU abbreviation | Vul |
| Visibility from Lewes (50.87 degrees N) | Yes. All parts of its IAU region rise at some time of year, although some southern objects may remain very low. |
| Representative brightest star | Anser (Alpha Vulpeculae) |
How to read these star and deep-sky measurements
| Role | Representative brightest star |
|---|---|
| Common / proper name | Anser |
| Latin / catalogue designation | Alpha Vulpeculae |
| Apparent magnitude (V) | 4.45 |
| Spectral type | M0.5IIIb |
| Distance from Earth | About 290ly |
| RA (ICRS / J2000) | 19h28m42s |
| Declination (ICRS / J2000) | +24d39m54s |
| Among the ten brightest night-sky stars? | No, in the reference top-ten list. |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 64 degrees. |
Distance is a rounded estimate from the catalogue parallax.
Sources: SIMBAD: Anser
| Object type | Planetary Nebula |
|---|---|
| Distance from Earth | 1,200ly |
| RA (J2000; approximate centre) | 19h59m36s |
| Declination (J2000; approximate centre) | +22d43m00s |
| Visibility from Lewes | Can be seen at a suitable season and time; maximum altitude about 62 degrees. |
Distances are approximate reference estimates and can differ between studies. Coordinates identify the approximate centre of an extended object; they do not describe its full extent.
See Reading constellation profiles for the coordinate conventions, brightness ranking and visibility method. Visibility means geometrically above an unobstructed horizon at some suitable time of year, not necessarily tonight or with the naked eye.
Sources: IAU: the 88 constellations
Other names and search terms: Keck, Keck Observatory
A pair of large optical and infrared telescopes using segmented primary mirrors and advanced instruments, including adaptive optics.
| Location | Near the summit of Maunakea, Hawai'i Island, Hawai'i, USA |
|---|---|
| Type of site | Optical and infrared research observatory |
| Main instruments or facilities | Two 10m primary mirrors, each built from 36 hexagonal segments |
| Observing wavelengths | Visible and infrared |
| Scientific or historical importance | High-resolution studies of stars, exoplanets, galaxies and the Galactic Centre |
Sources: Keck: telescopes; Keck: location and instrumentation
The compact, hot remnant left after a low- or intermediate-mass star sheds its outer layers. A white dwarf has roughly Earth-sized dimensions but a substantial fraction of a star's mass. It shines mainly by releasing stored heat, rather than sustained core fusion. The faint companion in the Sirius binary is a nearby example.
High-energy electromagnetic radiation with wavelengths shorter than ultraviolet. Astronomical X-rays often come from very hot gas and energetic regions around compact objects. Earth's atmosphere blocks them, and X-ray telescopes commonly use mirrors that reflect radiation at very shallow angles.
Sources: Chandra: X-ray telescope design
Other names and search terms: XMM, X-ray Multi-Mirror Mission
An ESA X-ray observatory with three nested-mirror telescopes, designed to collect many X-ray photons for imaging and spectroscopy. It also carries an optical and ultraviolet monitor.
| Agency or partnership | ESA |
|---|---|
| Science orbit / location | Highly elliptical Earth orbit |
| Main telescope or instruments | Three X-ray mirror modules, each with 58 nested shells and an outer diameter of about 0.7m; 0.3m optical/UV monitor |
| Observing wavelengths | X-rays, with complementary ultraviolet and optical observations |
| Mission history | Launched in 1999 |
| Scientific importance | Spectroscopy of hot gas, black-hole environments, stars and galaxy clusters |
Orbit descriptions refer to the science mission. Retired spacecraft may be in a different disposal orbit. Sizes describe the stated mirror, aperture or detector system and should not be treated as directly equivalent collecting areas.
Sources: ESA: XMM-Newton telescopes; ESA: XMM-Newton operations
The first human to travel into space and orbit Earth. His Vostok 1 mission on 12 April 1961 lasted approximately 108 minutes, opening the era of human spaceflight.
| Dates | 1934-1968; historic flight 1961 |
|---|---|
| Background | Soviet cosmonaut |
The point in the sky directly above the observer, at an altitude of 90 degrees.