The Zodiac --- The Constellation of Cancer the Crab

 

Cancer The Crab is the fourth constellation of the Zodiac. Astronomically, the Sun is now in Cancer from the 21st of July to the 9th of August, but in days of yore the Sun entered Cancer at the time of the Summer Solstice in June. Thus, the opening of the Summer season in the Northern Hemisphere was known (and is still sometimes referred to) as The First Point of Cancer. The Tropic of Cancer marks the point where the Sun's direct rays reach their northernmost point on June 21st.

Cancer is a small and dim constellation. None of its stars exceed the Fourth Magnitude, making it hard to see at the best of times. It has a very ill-defined Y-shaped asterism that makes up the body of the crab, but in Sumeria the starfield that is Cancer was not identified as any thing. Instead, that area of the sky was simply referred to as "The Realm of Anu" (the sky-god and father of the rest of the gods). Cancer was thus intimately linked to the stars and to the Sun, and Sumerian astrologers made the Moon the ruler of Cancer. Thus, although it had no bright stars itself and was sometimes referred to as "The Dark Stars" this early summer constellation was tied to all the sources of light in the sky. 

Later Mesopotamians decided that the Cancer starfield was actually the glittering Throne of Anu, and it is recorded as such in Assyrian and Babylonian texts. Despite its ill-definition it was clearly an important constellation. 

 

Anu was also known as El; this is the name used in later Mesopotamian records, among Canaanites, and among the early Hebrews (who applied it to the One God they worshiped). It is still a titular name for God in Judaism (i.e., "Beth-El" = "House of God").

The Egyptians, who were not worshipers of Anu, saw the asterism of Cancer not as a crab but as a crayfish, and the constellation appears as a crayfish in many star catalogues of the 16th-19th Centuries. It is, however, "The Crab" in the Nautical Almanac. 

 

It was the Greeks who called the constellation Cancer The Crab, and they associated it with the Twelve Labors of Hercules, one of which was slaying a giant crab monster. "Cancer" means "crab." Ancient Greek physicians who were advanced enough to extract tumors from the human body noted that in many cases the tumors put out tentacles to ensnare healthy tissue. Noting a resemblance to the generally unlovely multilegged and clawed arthropods they knew, they called the tentacled tumors "cancers" and the word has descended to us unchanged. 

Cancer may not be an impressive constellation, but it is home to several deep-sky objects, the most prominent of which is the Beehive Cluster at its center.