|Right ascension||07h 55m 19.7973s–09h 22m 35.0364s|
|Area||506 sq. deg. (31st)|
|Stars with planets||10|
|Stars brighter than 3.00m||0|
|Stars within 10.00 pc (32.62 ly)||2|
|Brightest star||β Cnc (Altarf) (3.53m)|
|Nearest star||DX Cnc
(11.84 ly, 3.63 pc)
|Meteor showers||Delta Cancrids|
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. Its name is Latin for crab and it is commonly represented as one. Its astrological symbol is (Unicode ♋). Cancer is a medium-size constellation with an area of 506 square degrees and its stars are rather faint. It lies between Gemini to the north and Leo to the south, Lynx to the east and Canis Minor and Hydra to the west.
Cancer, or the Crab, is one of the constellations of the zodiac. It is a medium size constellation with mostly faint stars that lies in the northern hemisphere. In Greek mythology, Cancer is identified with the crab that appeared while Hercules was fighting the many-headed Hydra. The crab bit Hercules on the foot, Hercules crushed it and then the goddess Hera, a sworn enemy of Hercules, placed the crab among the stars.
The Cancer constellation occupies an area of 506 square degrees and contains two stars with known planets. It can be seen at latitudes between +90° and -60° and is best visible at 9 p.m. during the month of March.
The brightest star in the Cancer constellation is  beta Cancri, also known as Tarf or Al Tarf, with an apparent magnitude of 3.50. The primary component is an orange K-type giant 290 light-years distant from Earth. The magnitude 14 companion is located 29 seconds away.
At magnitude 3.94,  delta Cancri, is the second brightest star. It is an orange giant that also goes by the name Asellus Australis, or "southern donkey colt." 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." Delta Cancri also makes it easy to find X Cancri, the reddest star in the sky.
 iota Cancri, with a magnitude of 4.03, is another star brighter than  alpha Cancri. It is a binary star composed of a yellow G-type bright giant and an A-type main sequence dwarf. Both can easily be seen with a small telescope.
 gamma Cancri or Asellus Borealis ("northern donkey colt") is a magnitude 4.6 white A-type subgiant about 158 light-years distant from Earth.
 alpha Cancri or Acubens ("the claws") is a star system that lies 173 light-years away and has magnitude of 4.26. It is also sometimes known as Sertan ("the crab"). The star’s primary component is a white A-type main sequence dwarf, while the companion is a magnitude 11 star.
Zeta Cancri or Tegmine ("the shell") is another star system, one that contains at least four stars.  zeta 1 Cancri consists of two yellow-white main sequence dwarfs (zeta Cancri A and B), while  zeta 2 Cancri contains a yellow G-type star (zeta Cancri C) and a magnitude 10 companion that is either a red dwarf or a close pair of red dwarfs.
The Cancer constellation also has several notable deep sky objects. Praesepe, or the Beehive Cluster, is a very popular feature among astronomers. Also known as Messier 44, M44, NGC 2632 or Cr 189, the Beehive Cluster is located right in the centre of the Cancer constellation. It is an open star cluster, one of the nearest ones to our solar system. It is most easily observed when Cancer is high in the sky. North of the Equator, this period stretches from February to May. Ptolemy described the Beehive Cluster as "the nebulous mass in the breast of Cancer." It was one of the first objects Galileo observed with his telescope in 1609, spotting 40 stars in the cluster. Today, there are about 1010 high-probability members, most of them (68 percent) red dwarfs. The Greeks and Romans identified the nebulous object as a manger from which two donkeys, represented by the neighbouring stars  Asellus Borealis and  Asellus Australis, were eating. The stars represent the donkeys that the god Dionysus and his tutor Silenus rode in the war against the Titans. The ancient Chinese interpreted the object as a ghost or demon riding in a carriage, calling it a "cloud of pollen blown from under willow catkins."
Another notable feature in the Cancer constellation is  rho-1 Cancri or 55 Cancri, 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.
Cancer belongs to the Zodiac family of constellations, along with Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces, Aries, Taurus and Gemini.
Constellations directly bordering Cancer are Lynx, Gemini, Canis Minor, Hydra, Leo and Leo Minor.
- α Cnc (Acubens) is a double star with a primary of magnitude 4.3, 173 light-years from Earth. The secondary is of magnitude 12.0 and is visible in small amateur telescopes. Its common name means "the claw".
- β Cnc (Altarf) is the brightest star in Cancer at magnitude 3.5. It is an orange-hued binary star system consisting of a K-type orange giant and a red dwarf located 290 light-years from Earth. Altarf represents a part of Cancer's body.
- γ Cnc (Asellus Borealis) is a white-hued star of magnitude 4.7, 158 light-years from Earth. Its common name means "northern donkey".
- δ Cnc (Asellus Australis) is an orange-hued giant star of magnitude 3.9, 136 light-years from Earth. Its common name means "southern donkey".
- ζ Cnc is a multiple star system 83 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 star of magnitude 70000.0 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 59.5 years; its primary is of magnitude 5.6 and its secondary is of magnitude 6.0. This pair will be at its greatest separation in 2018.
- ι Cnc is a wide double star. The primary is a yellow-hued giant star of magnitude 4.0, 298 light-years from Earth. The secondary is a blue-white hued star of magnitude 6.6.
- 55 Cnc has a quintuple planet system with one super-earth and four gas giants, one of which is in the habitable zone and as of such has expected temperatures similar to Earth.
Cancer is best known among stargazers as the home of Praesepe (Messier 44), an open cluster also called the Beehive Cluster, 577 light-years from Earth. M44 contains about 50 stars, the brightest of which are of the sixth magnitude. ε Cnc 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.
The smaller, denser open cluster Messier 67 can also be found in Cancer, 2500 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.
Cancer is said to have been the place for the Akkadian Sun of the South, perhaps from its position at the summer solstice in very remote antiquity. But afterwards it was associated with the fourth month Duzu (June–July in the modern western calendar), and was known as the Northern Gate of Sun.
Showing but few stars, and its brightest stars being of only 4th magnitude, Cancer was often considered the "Dark Sign", quaintly described as black and without eyes. Dante, alluding to this faintness and position of heavens, wrote in Paradiso:
Then a light among them brightened,
Cancer was the location of the Sun's most northerly position in the sky (the summer solstice) in ancient times, though this position now occurs in Taurus due to the precession of the equinoxes, around June 21. This is also the time that the sun is directly overhead at 23.5°N, a parallel now known as the Tropic of Cancer.
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 represent Cancer as 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 much 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.
|This section does not cite any references or sources. (December 2008)|
In Ancient Greece, Aratus called the crab Καρκινος (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 Καρκινος, Ονοι, και Φατνη (Karkinos, Onoi. kai fatne): the Crab, Asses, and Crib.
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 Karkatan, and in Sinhalese Kagthaca. The later Hindus knew it as Kulira, from the Greek Κολουρος (Koloyros), the term originated by Proclus.
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 crab, lobster, or scorpion.
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.
The creation of the constellation is explained in Greek mythology by the short-lived association of the crab Karkinos with one of the Twelve Labors of Hercules, in which Hercules battled the multi-headed Lernaean Hydra. Hera had sent Karkinos to distract Hercules and put him at a disadvantage during the battle, but Hercules quickly dispatched the crab by kicking it with such force that it was propelled into the sky. Other accounts had Karkinos grabbing onto Hercules' toe with its claws, but Hercules simply crushed the crab underfoot. Hera, grateful for Karkinos' effort, gave it a place in the sky. Some scholars have suggested that Karkinos was a late addition to the myth of Hercules in order to make the Twelve Labors correspond to the twelve signs of the Zodiac.
As of 2002[update], the Sun appears in the constellation Cancer from July 21 to August 9. In tropical astrology, the Sun is considered to be in the sign Cancer from June 21 to July 22, and in sidereal astrology, from July 16 to August 15.
In the 1998 Sega arcade game The Ocean Hunter, Karkinos is featured therein as one of seven boss characters. Though Karkinos is depicted in the game as resembling a giant red king crab, its species is listed therein as Macrocheira kaempferi, or the Japanese spider crab.
In the final book in the Percy Jackson & the Olympians series, The Last Olympian, Percy Jackson fights a giant crab (Karkinos) on board the Titan cruise ship Princess Andromeda. He kills it by stabbing its underbelly, its only uncovered, vulnerable point.
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- (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 27 日
- The Ocean Hunter - Stage 5 (YouTube)
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|Wikimedia Commons has media related to:|
- The Deep Photographic Guide to the Constellations: Cancer
- Star Tales – Cancer
- Cancer Constellation at Constellation Guide