constellation n.

early 14c., constellacioun, "position of a planet in the zodiac;" late 14c., "one of the recognized star patterns handed down from antiquity" (in the zodiac or not), from Old French constellacion "constellation, conjuncture (of planets)" and directly from Late Latin constellationem (nominative constellatio) "a collection of stars," especially as supposed to exert influence on human affairs," from constellatus "set with stars," from assimilated form of Latin com "with, together" (see con-) + past participle of stellare "to shine," from stella "star" (from PIE root *ster- (2) "star").

The oldest sense is astrological, of the position of planets ("stars") relative to the zodiac signs on a given day, usually the day of one's birth, as a determiner of one's character. "I folwed ay myn inclinacioun/By vertu of my constillacioun" (Chaucer, "Wife's Prologue," c. 1386). In modern use "a group of fixed stars to which a definite name has been given but does not form part of another named group (compare asterism). Figuratively, "any assemblage of a brilliant or distinguished character"(1630s).

The classical northern constellations probably were formed in prehistoric Mesopotamia; the Greeks likely picked them up c. 500 B.C.E., and Claudius Ptolemy (c. 90-c. 168) of Alexandria codified 48 of them, all still current, in his "Almagest" (2c.). The canonical list was expanded from 16c. as Europeans explored southern regions whose stars were invisible from Alexandria and as astronomers filled in the dimmer regions between the established figures, so that by the late 19c. as many as 109 constellations were shown on maps. The modern roster was set at 88 by the International Astronomical Union in 1922.