A constellation is group of stars
that appear to form a configuration in the sky; properly speaking, a constellation is a definite region of the sky in which the configuration of stars is contained. Identifiable groupings of bright stars have been recognized and named since ancient times, the names corresponding to mythological figures (e.g., Perseus, Andromeda, Hercules, Orion), animals (e.g., Leo the Lion, Cygnus the Swan, Draco the Dragon), or objects (e.g., Libra the Balance, Corona the Crown). Ptolemy listed 48 constellations in his
Almagest
(2d cent. AD). As systematic observations were extended to the entire southern sky from the 17th cent. on, more constellations were added to the list by J. Bayer, N. L. de Lacaille, and others. For example, Ptolemy's 48th constellation, Argo Navis, representing a ship, was divided into four smaller constellations corresponding to different parts of the ship. The final list consists of 88 constellations, each associated with a definite region of the sky. Thus, the entire celestial sphere is divided according to a plan prepared by Eugene Delporte, with the boundaries fixed by international agreement in 1930, along lines of right ascension and declination. The 12 constellations located along or near the ecilhe apparent path of the sun through the heavens, are known as the constellations of the zodiac; the remaining constellations are officially classified as northern (28 constellations) or southern (48 constellations).
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