Cancer (constellation)

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". 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). 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 zodiacal constellations, having only two stars above the fourth magnitude. Also known as Altarf or Tarf, Beta Cancri is the brightest star in Cancer at apparent magnitude 3.5. Located 290 ± 30 light-years from Earth, An aging star, it has expanded to around 50 times the Sun's diameter and shines with 660 times its luminosity. It has a faint magnitude 14 red dwarf companion located 29 arcseconds away that takes 76,000 years to complete an orbit. 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. Its common name means "southern donkey". that is 35 times as luminous as of the Sun. It is located 181 ± 2 light-years from Earth. Located 181 ± 2 light-years from Earth, Zeta Cancri or Tegmine ("the shell") is a multiple star system that contains at least four stars located 82 light-years from Earth. The two brightest components are a binary star with an orbital period of 1100 years; the brighter component is a yellow-hued binary pair and the dimmer component is a yellow-hued star of magnitude 6.2. The brighter component is itself a binary star with a period of 59.6 years; its primary is of magnitude 5.6 and its secondary is of magnitude 6.0. This pair is at its greatest separation around 2019. more than six times the value calculated for the previous largest object. ==History and mythology==

Cancer was first recorded by Claudius Ptolemy in the in The Mathematical Syntaxis (a.k.a. Almagest), under the Greek name (Karkinos). In the late 1890s, R. H. Allen asserted the following, with no supporting citation: :"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 , our June–July, and was known as the Northern Gate of Sun ..." Very few of Cancer's stars are visible to the naked eye, and its brightest stars are only 4th magnitude. Cancer was often considered the "Dark Sign", quaintly described as "black and without eyes". Dante, alluded to its faintness in Paradiso, and mentioned it being visible for the whole night when it culminated at midnight in a Northern Hemisphere winter month: :Then a light among them brightened, :so that, if Cancer one such crystal had, :winter would have a month of only a day. Cancer was the backdrop to the Sun's most northerly position in the sky (the summer solstice) in ancient times, when the Earth's Sun-facing side was maximally tilted towards the south, in the Gregorian calendar kept within a few days of June 21. Equivalently, this is the date when the Sun is directly overhead as far north as 23.437° N. The northern-most parallel where the Sun is directly overhead is still called the Tropic of Cancer, even though the corresponding position on the sky now occurs in Taurus, due to the precession of the equinoxes. ==Illustrations==

, a set of constellation cards published in London c. 1825 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. In the 12th century, an illustrated astronomical manuscript shows it as a water beetle. Albumasar writes of this sign in ''Flowers of Abu Ma'shar''. A 1488 Latin translation depicts cancer as a large crayfish, which also is the constellation's name in most Germanic languages. Jakob Bartsch and Stanislaus Lubienitzki, in the 17th century, described it as a lobster. ==Names==

R.H. Allen, in Star Names: Their lore and meanings, lists names for the constellation as follows: :In Ancient Greece, Aratus called the crab (Karkinos), which was followed by Hipparchus and Ptolemy. The Alfonsine tables called it Carcinus, a Latinized form of the Greek word. Eratosthenes extended this as , , (Karkinos, Onoi, kai Fatne): the Crab, Asses, and Crib. In Ancient Rome, Manilius and Ovid called the constellation Litoreus (shore-inhabiting). Astacus and Cammarus appear in various classic writers, while it is called Nepa in Cicero's De Finibus and the works of Columella, Plautus, and Varro; all of these words signify a crab, lobster, or scorpion. :Athanasius Kircher said that in Coptic Egypt it was (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. :The Indian language Sanskrit shares a common ancestor with Greek, and the Sanskrit name of Cancer is Karka and Karkata. In Telugu it is "Karkatakam", in Kannada "Karkataka" or "Kataka", in Tamil Kadagam, and in Sinhala . The later Hindus knew it as Kulira, from the Greek (Kolouros), the term originated by Proclus. ==Astrology==

, the Sun appears in the constellation Cancer from July 20 to August 9. In tropical astrology, the Sun is considered to be in the sign of Cancer from June 22 to July 22, and in sidereal astrology, from July 16 to August 16. The symbol of the astrological sign (which now covers roughly the constellation of Gemini) is (♋︎). ==Equivalents==

In Chinese astronomy, the stars of Cancer lie within the Vermilion Bird of the South (南方朱雀, Nán Fāng Zhū Què). ==See also==