CEPHEUS, in Greek mythology, the father of Andromeda (q.v.); in astronomy, a constellation of the northern hemisphere, mentioned by Eudoxus (4th century B.C.) and Aratus (3rd century B.C.). Ptolemy catalogued 13 stars in this constellation, Tycho 11, and Hevelius 51. The most interesting star in it is δ Cephei, a remarkable double star, the brighter component of which is a short period variable (5·37 days), with a range in magnitude of 3·7 to 4·9; it is also a spectroscopic binary.