Cancer Constellation

cancer constellation

   Cancer means “the crab” in Latin. It is the faintest of the zodiac constellations.   

   Cancer is the 31st largest constellation in the sky, occupying an area of 506 square degrees.



   Cancer is visible in the northern hemisphere in the early spring. It can be seen in the southern hemisphere during autumn.   It lies in the second quadrant of the northern hemisphere and can be seen at latitudes between +90° and -60°.

   Cancer is located between the Leo constellation (to its east) and the Gemini constellation (to its west). Other neighboring constellations are Canis Minor and Hydra (to the south), Leo Minor and Lynx (to the north).
   The brightest star in the Cancer constellation is Al Tarf (Beta Cancri). The star’s name is believed to be derived either from the Arabic aṭ-ṭarf, which means “the eye,” or aṭ-ṭarfah, which means “the glance (of Leo).” It is a binary star that consists of an orange K-type giant and a fourteenth magnitude companion is located 29 seconds away. Beta Cancri is approximately 290 light years distant.
   Asellus Australis (Delta Cancri) is the second brightest star. Its name means “southern donkey colt” in Latin. 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 is an orange giant 180 light years distant. It lies close to the ecliptic.  
   Asellus Borealis (Gamma Cancri) is a white A-type subgiant about 158 light years distant from Earth. Its name means “northern donkey colt.”  Gamma Cancri is also located near the ecliptic.   Acubens (Alpha Cancri) is only the fourth brightest star in Cancer. Its name means “the claws.”  It is sometimes also known as Al Zubanah or Sertan. The name Al Zubanah comes from the Arabic az-zubānah, which means “claws,” while Sertan is derived from saraţān, which means “the crab.” Alpha Cancri is a multiple star system located approximately 174 light years from Earth. The brightest component, Alpha Cancri A, is a white A-type main sequence dwarf while the companion, Alpha Cancri B is an eleventh magnitude star. Acubens has a luminosity 23 times that of the Sun. The star also lies close to the ecliptic.   Tegmine (Zeta Cancri) is a multiple star system approximately 83.4 light years from Earth. It is composed of two binary stars, Zeta-1 Cancri and Zeta-2 Cancri. Zeta-1 Cancri consists of two yellow-white main sequence dwarfs (Zeta Cancri A and B), Zeta-2 Cancri contains a yellow G-type star (Zeta Cancri C) and a 10th magnitude red dwarf (Zeta Cancri D).  Its name means “the shell of the crab.”  

   Cancer’s most famous deep sky object is Messier 44, also known as the Beehive Cluster, which is a small open star cluster, one of the nearest ones to our solar system. It resembles a swarm of bees. The Beehive Cluster is also called Praesepe, which means “the manger” in Latin. Also known as M44, NGC 2632 or Cr 189, the Beehive Cluster is located right in the center of the Cancer constellation. The Beehive Cluster is about 577 light years from Earth and its estimated age is 600 million years. Praesepe contains at least a thousand stars. More than a half of them (63%) are red dwarfs, and about a third (30%) are Sun-like. The brightest stars in the cluster are blue-white in color.

   The constellation’s other deep space object, Messier 67, is another open star cluster. It is one of the oldest open clusters known. Its estimated age is between 3.2 and 5 billion years. M67 contains over 100 stars similar to the Sun and a number of red giants. Almost all the stars in the cluster are roughly at the same distance and of the same age, which makes M67 one of the most observed and studied objects by those studying stellar evolution.

   Another notable feature in the Cancer constellation is 55 Cancri, a binary star approximately 40.9 light years distant from Earth. It consists of a yellow dwarf and a smaller red dwarf. 55 Cancri is notable because, as of 2010, astronomers have confirmed five extrasolar planets- one terrestrial planet and four gas giants- orbiting the primary star in the system, the yellow dwarf known as 55 Cancri A. This is one of the four known planetary systems in our solar system discovered to have at least five planets. The planet nearest to the star is believed to be a terrestrial planet with a mass similar to Neptune, while the outermost planets are believed to be Jovian planets, with masses comparable to that of Jupiter. 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.   



   In Greek myth, the story of the Crab is not a tale of heroic glory, but rather a celebration of loyalty, persistence and determination. The story begins with Zeus having an affair with Alcmene, the queen of Tiryns. The result of this union was the Hercules, the most famous Greek Hero. Of course, this union and offspring did not go over too well with Hera, the wife of Zeus. Hera, in her jealous state, swore to kill Hercules. Hera attempted to have Hercules killed many times but his imposing strength allowed him to overcome.    

   So, Hera cast a spell of madness on Heracles, causing him to commit a great crime. In order to be forgiven, he had to perform twelve difficult tasks. One of these tasks was destroying the terrible nine-headed water-serpent, Hydra. The giant crab nipped at Hercules feet to divert his attention from Hydra. However, Hercules killed the crab by crushing its shell with his feet. Although Hera is regarded as one of the most ungrateful of the Greeks, she was pleased with the services of the crab and rewarded it by placing it in the sky. Hera places the crab in a region of the sky that has no bright stars, because despite its efforts, the crab was not successful in accomplishing the task. 

   The Scriptures of Delphi has a different version. A different explanation behind the mythology of Cancer.

   According to the Scriptures, a giant crab named Crios guarded the sea nymphs in the Greek god Poseidon’s kingdom. He was enormous and strong, and Poseidon himself had blessed him with immortality. 

   When the god of monsters Typhon terrorized the gods of Olympus, Poseidon, along with most of the other gods, went into hiding. He left Crios in charge of protecting the sea nymphs, who were considered to be Poseidon’s daughters. The crab took his role as protector very seriously, and wouldn’t let any of the sea nymphs outside of his reach. After a while, some of the sea nymphs became restless, and convinced that they were in no danger from Typhon, escaped into the open sea.

   Crios could not chase them as he was charged with protecting the other sea nymphs, so he enlisted the help of the giant squid, Vamari.  Little did he know that Vamari, whose name translates to “Vampire Squid,” had ill intentions, and when he caught up to the sea nymphs, he devoured them.

   When Vamari returned to Crios, he told the crab that despite a valiant effort, he could not find any of the missing sea nymphs. Crios knew that he was lying and attacked him. They battled for hours until the crab finally won. But he had sustained such bad injuries that he was terribly crippled from that time forward. Since  he was immortal, though, he could not die, but had to live in pain.

   When Poseidon returned, he saw the bravery that the crab had shown and relieved him of his pain, but not his immortality, by placing him in the sky as the constellation of Cancer.


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