Any of certain groupings of star s that were imagined by those who named them to form images of objects, mythological figures, or creatures in the sky.
They are useful in helping sky gazers and navigators locate certain stars. A constellation's stars are often designated by its name and letters of the Greek alphabet in order of brightness. Of 88 named constellations in Western astronomy, about half retain the names Ptolemy gave the 48 he identified in his Almagest . See also zodiac .