ANDROMEDA, in Greek legend, the daughter of Cepheus • and Cassiopeia (q.v.). To satisfy Poseidon, who had been offended, Andromeda, chained to a rock, was exposed to a sea monster. Perseus, returning from having slain the Gorgon, found her, slew the monster, set her free, and married her in spite of Phineus, to whom she had before been promised (Ovid, Metam., v. I). An dromeda followed her husband to Tiryns in Argos, and became the ancestress of the family of the Perseidae. After her death she was placed by Athena amongst the constellations in the northern sky, near Perseus and Cassiopeia. Sophocles and Euripides (and in modern times Corneille) made the story the subject of trage dies, and its incidents were represented in numerous ancient works of art.
The most famous feature of the astronomical constellation is the Great Andromeda Nebula—the brightest of the spiral nebulae. It can be seen without much difficulty with the naked eye and recognized by its diffuse appearance. It is an "island universe" probably containing millions of stars and of the same general nature as our own stellar system, though apparently of somewhat smaller dimensions. (See NEBULA.) From the brightness of the Cepheid variables in the nebula, Hubble has deduced that its distance is 900,000 light-years. A number of outbursts of Novae (temporary stars) have been observed in the nebula. Nearly all the spiral nebulae are receding from us with large velocities, but the Andromeda nebula is one of the exceptional approaching sys tems, its velocity in the line of sight being 30o kilometres per second. Photographs show in great detail its beautiful spiral struc ture; the plane of the spiral is tilted with respect to us, giving the nebula an apparently elongated form.
The double star y Andromedae is a favourite object for obser vation with a small telescope on account of the striking contrast of colour of the two components.
The Andromedids are a swarm of meteors which made a notable display on Nov. 27 1872, and provide some of the November meteors year by year; the swarm is believed to be the debris of Biela's comet which was last seen in 1852.