Constellation

Constellation, any of 88 imagined groupings of stars that appear on the celestial sphere and that are named after religious or mythological figures, animals, or objects. The term also refers to the delimited areas on the celestial sphere that contain the named groups of stars.

The oldest known drawings of constellations are motifs on seals, vases, and gaming boards of the Sumerians, indicating that constellations may have been established as early as 4000 bc. The constellation Aquarius was named by the Sumerians after their god An, who pours the waters of immortality upon the Earth. The zodiac was divided into 12 equal signs by around 450 bc by the Babylonians. The northern constellations of today are little different from those known to the Chaldeans and the ancient Egyptians, Greeks, and Romans. Homer and Hesiod mentioned constellations, and the Greek poet Aratus of Soli (c. 315-c. 245 bc) gave a verse description of 44 constellations in his Phaenomena. The Greek astronomer and mathematician Ptolemy, in his Almagest, described 48 constellations, of which 47 are known today by the same names.

In the past many other peoples have grouped stars into constellations, although their arrangements usually did not correspond to those of the ancient West. Some Chinese constellations, however, resemble Western ones, indicating the possibility of a common origin.

At the end of the 16th century the first European explorers of the South Seas mapped the southern sky. New constellations were added by a Dutch navigator, Pieter Dirckz Keyser, who participated in the exploration of the East Indies in 1595. Subsequently, other southern constellations were added by the German astronomer Johann Bayer, who published the first extensive star atlas in the Western world, the Uranometria; by Johannes Hevelius; and by the French astronomer Nicolas Louis Lacaille. Many others proposed new constellations, but astronomers finally settled on a list of 88. The boundaries of constellations, however, remained a matter of discussion until 1930, when definitive boundaries were fixed by the International Astronomical Union.

The genitive forms of the names of constellations, preceded by a Greek letter, are used to designate about 1,300 bright stars; this system was introduced by Johann Bayer. The famous star Algol in the constellation Perseus, for example, is called Beta Persei. The accompanying table lists the constellations on which separate articles appear in this encyclopedia.