The origin of Cancer's name is derived from the Latin meaning for "Crab." It is an ancient constellation, probably Babylonian in origin, and listed as one of the forty-eight constellations compiled by Claudius Ptolemy during the Second Century A.D. In Ancient Egypt, this group of stars represented two turtles or sometimes an obscure water creature known as the Allul. During the Seventeenth Century, some cultures referred to Cancer as a lobster or even a crayfish. This dim constellation, the faintest of the entire Zodiac, contains no stars brighter than fourth magnitude, none of which are distinguishable by the naked eye. Quite possibly, Cancer's only claims to fame is inclusion in the Signs of the Zodiac and the beautiful Praesepe (meaning "hive," "crib" or "manger"), also known as the Beehive Cluster. In earlier times, this Cluster was also referred to as "Little Cloud" and "Little Mist" and was the basis of an early method of forecasting the weather. According to Pliny, if Praesepe were not visible in a clear sky, then it foretold the coming of a violent storm. The astronomers of both Ancient Greece and Ancient Arabia perceived the Beehive Cluster as the crib of the infant Jesus, with two of the nearby stars (known collectively as the "Aselli" or "Asses") on either side representing donkeys (or maybe a donkey and an ox) feeding on hay from the manger.

The Chaldeans associated this region of the heavens with a crab because such creatures walk sideways and then backward, rather like the Sun appears to move as it reaches the Solstice and turns Southward. Possibly associated with a similar belief, the Ancient Egyptians thought of this area of the sky as a scarab, in reference to their concept that an invisible celestial scarab beetle pushed the Sun across the heavens. The constellation of Cancer was also referred to by some ancient philosophers as the "Gate of Men" through which, so it was said, the souls of people descended to Earth in order to enter human bodies. To the Ancient Japanese, who regarded the grouping as a "lump of souls," the Beehive Cluster was a truly terrifying sight.

One of the sky's largest and finest open clusters, the Beehive is easily found with the aid of binoculars and can be spotted with the naked eye, provided one is in a dark location. Its size is equivalent to three full Moons, end-to-end, and is so large that it was once thought to be a nebula. Galileo was the first to study its stars with a telescope, counting over forty members. It was later determined that the Beehive, in fact, contains more than three three hundred stars, over a hundred of which are brighter than the Sun. In 1531 Halley's Comet was discovered in this part of the sky and, in the Summer of 1895, all of the planets with the exception of Neptune congregated in this area...an event of extreme rarity. According to some cultural legends, when all the planets meet in Cancer, then the world will come to an end by means of a devastating flood.

The Sun passes through Cancer from late July to early August. In earlier times, the Sun formerly lay in this constellation when it reaches the point farthest North...the time of the Summer Solstice and the origin of the naming of the Tropic of Cancer. Today, however, the Sun lies in the neighboring constellation of Gemini during the Summer Solstice (due to the effect of precession) but the Tropic of Cancer label persists, nonethless. Cancer is associated with the constellation family of Hercules.

A Northern constellation located between Gemini the Twins and Leo the Lion, Cancer is also bordered by Canis Minor the Little Dog, Hydra the Sea-Serpent, Leo Minor the Little Lion, Ursa Major the Great Bear and Lynx the Lynx.