Cancer (constellation)
Constellation | |
31st) | |
Main stars | 5 |
---|---|
Bayer/Flamsteed stars | 76 |
Stars with planets | 10 |
Stars brighter than 3.00m | 0 |
Stars within 10.00 pc (32.62 ly) | 2 |
Brightest star | β Cnc (Tarf) (3.53m) |
Messier objects | 2 |
Meteor showers | Delta Cancrids |
Bordering constellations | Lynx Gemini Canis Minor Hydra Leo Leo Minor (corner) |
Visible at latitudes between +90° and −60°. Best visible at 21:00 (9 p.m.) during the month of March. |
Cancer is one of the twelve constellations of the zodiac and is located in the Northern celestial hemisphere. Its old astronomical symbol is (♋︎). Its name is Latin for crab and it is commonly represented as one. Cancer is a medium-size constellation with an area of 506 square degrees and its stars are rather faint, its brightest star Beta Cancri having an apparent magnitude of 3.5. It contains ten stars with known planets, including 55 Cancri, which has five: one super-earth and four gas giants, one of which is in the habitable zone and as such has expected temperatures similar to Earth. At the (angular) heart of this sector of our celestial sphere is Praesepe (Messier 44), one of the closest open clusters to Earth and a popular target for amateur astronomers.
Characteristics
Cancer is a medium-sized constellation that is bordered by Gemini to the west, Lynx to the north, Leo Minor to the northeast, Leo to the east, Hydra to the south, and Canis Minor to the southwest. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Cnc".[3]
The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of 3 main and 7 western edgework forming sides (illustrated in infobox). In the equatorial coordinate system, the right ascension coordinates of these borders lie between 07h 55m 19.7973s and 09h 22m 35.0364s, while the declination coordinates are between 33.1415138° and 6.4700689°.[2] Covering 506 square degrees or 0.921% of the sky, it ranks 31st of the 88 constellations in size. It can be seen at latitudes between +90° and -60° and is best visible at 9 p.m. during the month of March. Cancer borders the bright constellations of Leo, Gemini and Canis Minor. Under city skies, Cancer is invisible to the naked eye.
Features
Stars
Cancer is the dimmest of the
Also known as Altarf or Tarf,
At magnitude 3.9 is Delta Cancri, also known as Asellus Australis.[11] Located 131±1 light-years from Earth,[9] it is an orange-hued giant star that has swollen and cooled off the main sequence to become an orange giant with a radius 11 times and luminosity 53 times that of the Sun.[11] Its common name means "southern donkey".[1] The star also holds a record for the longest name, "Arkushanangarushashutu," derived from ancient Babylonian language, which translates to "the southeast star in the Crab."[citation needed] Delta Cancri also makes it easy to find X Cancri, the reddest star in the sky. Known as Asellus Borealis "northern donkey", Gamma Cancri is a white-hued A-type subgiant of spectral type A1IV and magnitude 4.67,[12] that is 35 times as luminous as of the Sun.[13] It is located 181 ± 2 light-years from Earth.[9]
Located 181 ± 2
Ten star systems have been found to have planets. Rho1 Cancri or 55 Cancri (or Copernicus[7]) is a binary star approximately 40.9 light-years distant from Earth. 55 Cancri consists of a yellow dwarf and a smaller red dwarf, with five planets orbiting the primary star; one low-mass planet that may be either a hot, water-rich world or a carbon planet and four gas giants. 55 Cancri A, classified as a rare "super metal-rich" star, is one of the top 100 target stars for NASA's Terrestrial Planet Finder mission, ranked 63rd on the list. The red dwarf 55 Cancri B, a suspected binary, appears to be gravitationally bound to the primary star, as the two share common proper motion.
YBP 1194 is a sunlike star in the open cluster M67 that has been found to have three planets.
Deep-sky objects
Cancer is best known among stargazers as the home of Praesepe (Messier 44), an open cluster also called the Beehive Cluster, located right in the centre of the constellation. Located about 590 light-years from Earth, it is one of the nearest open clusters to our Solar System. M 44 contains about 50 stars, the brightest of which are of the sixth magnitude. Epsilon Cancri is the brightest member at magnitude 6.3. Praesepe is also one of the larger open clusters visible; it has an area of 1.5 square degrees, or three times the size of the full Moon.[1] It is most easily observed when Cancer is high in the sky. North of the Equator, this period stretches from February to May.
The smaller, denser open cluster Messier 67 can also be found in Cancer, 2600 light-years from Earth. It has an area of approximately 0.5 square degrees, the size of the full Moon. It contains approximately 200 stars, the brightest of which are of the tenth magnitude.[1]
History and mythology
Cancer was first recorded by
In the late 1890s,
- "Cancer is said to have been the place for the Akkadian Sun of the South, perhaps from its position at the winter solstice in very remote antiquity; but afterwards it was associated with the fourth month Duzu [araḫ Dumuzu], our June–July, and was known as the Northern Gate of Sun ..."[19]
Very few of Cancer's stars are
- Then a light among them brightened,
- so that, if Cancer one such crystal had,
- winter would have a month of only a day.[20][full citation needed]
Cancer was the backdrop to the Sun's most northerly position in the sky (the
The close conjunction of Jupiter and Saturn in 1563 – which was observed by Tycho Brahe and led him to note the inaccuracy of existing ephemerides and to begin his own program of astronomical measurements – occurred in Cancer not far from Praesepe.
In Greek mythology, Cancer is identified with the crab that appeared while Heracles fought the many-headed Lernaean Hydra. Hercules slew the crab after it bit him in the foot. Afterwards, the goddess Hera, an enemy of Heracles, placed the crab among the stars.[21]
Illustrations
The modern symbol for Cancer represents the pincers of a crab, but Cancer has been represented as many types of creatures, usually those living in the water, and always those with an exoskeleton.
In the Egyptian records of about 2000 BC it was described as Scarabaeus (Scarab), the sacred emblem of immortality. In Babylonia the constellation was known as MUL.AL.LUL, a name which can refer to both a crab and a snapping turtle. On boundary stones, the image of a turtle or tortoise appears quite regularly and it is believed that this represents Cancer since a conventional crab has not so far been discovered on any of these monuments.
There also appears to be a strong connection between the Babylonian constellation and ideas of death and a passage to the underworld, which may be the origin of these ideas in later Greek myths associated with Hercules and the Hydra.[22]
In the 12th century, an illustrated astronomical manuscript shows it as a
Names
- In
- Athanasius Kircher said that in Coptic Egypt it was Κλαρια (Klaria), the Bestia seu Statio Typhonis (the Power of Darkness). Jérôme Lalande identified this with Anubis, one of the Egyptian divinities commonly associated with Sirius.[24]
- The Indian language
Astrology
As of 2002[update], the Sun appears in the constellation Cancer from July 20 – August 9. In
Equivalents
In
See also
- Cancer (Chinese astronomy)
Notes
References
- ^ a b c d e f g h i Ridpath & Tirion 2017, pp. 96–97
- ^ a b c "Cancer, constellation boundary". The Constellations. International Astronomical Union. Retrieved 14 February 2014.
- Bibcode:1922PA.....30..469R.
- ^ Wagman 2003, p. 60.
- ^ Bortle, John E. (February 2001). "The Bortle Dark-Sky Scale". Sky & Telescope. Retrieved 28 August 2017.
- ^ Ridpath, Ian. "Constellations: Andromeda–Indus". Star Tales. self-published. Retrieved 26 August 2015.
- ^ a b "Naming Stars". IAU.org. Retrieved 30 July 2018.
- ^ a b Kaler, James B. "Al Tarf (Beta Cancri)". Stars. University of Illinois. Retrieved 20 March 2014.
- ^ S2CID 18759600.
- ^ Watson, Christopher (3 May 2013). "NSV 3973". AAVSO Website. American Association of Variable Star Observers. Retrieved 20 March 2014.
- ^ a b Kaler, James B. (14 May 2010). "Asellus Australis (Delta Cancri)". Stars. University of Illinois. Retrieved 7 April 2015.
- ^ "gam Cnc". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 8 April 2015.
- S2CID 118665352.
- ^ a b Kaler, James B. "Iota Cancri". Stars. University of Illinois. Retrieved 29 May 2015.
- ^ Kaler, James B. "Acubens". Stars. University of Illinois. Retrieved 29 May 2015.
- S2CID 4412396. Archived from the original(PDF) on 8 September 2015. Retrieved 1 September 2015.
- ^ Shiga, David (10 January 2008). "Biggest black hole in the cosmos discovered". NewScientist.com news service.
- ISBN 9780718847814– via Google Books.
- Dover Books, New York, NY, and continually to the present.
- Quoted nearly verbatim by:
Bibcode:1911slaa.book.....O, citating Allen (1898/1899).- Later authors continue to repeat the same quote from Allen (1898/1899) to the present.
- The Divine Comedy.
- De Astronomica. 2.23.
- ^ White 2008, pp. 79–82
- ^ "Flowers of Abu Ma'shar". World Digital Library. 1488. Retrieved 15 July 2013.
- ^ a b c Allen 1899, pp. 107–108
- ^ 天文教育資訊網 2006 年 5 月 27 日. Activities of Exhibition and Education in Astronomy.
Bibliography
- Allen, Richard Hinckley (1899). "Cancer, the Crab". Star-names and Their Meanings. G.E. Stechert. pp. 107–114. Reprinted as Allen, Richard Hinckley (1963). Star Names: Their Lore and Meaning. Dover Publications. ISBN 0-486-21079-0.
- Ridpath, Ian; Tirion, Wil (2017). Stars and Planets Guide (5th ed.). Princeton University Press. ISBN 978-0-69-117788-5.
- Liungman, Carl G. (1994). Dictionary of Symbols. W. W. Norton & Company. ISBN 0-393-31236-4.
- White, Gavin (2008), Babylonian Star-lore, Solaria Pubs
- Wagman, Morton (2003). Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others. Blacksburg, Virginia: The McDonald & Woodward Publishing Company. ISBN 978-0-939923-78-6.
External links
- The Deep Photographic Guide to the Constellations: Cancer
- Ian Ridpath's Star Tales – Cancer
- Warburg Institute Iconographic Database (medieval and early modern images of Cancer)