Andromeda, Messier 31 (M31), is a spiral galaxy located about 2.5 million light years away. It is thought that the Milky Way and Andromeda will collide several billion years from now. The black holes located in both galaxies will then reside in the large, elliptical galaxy that results from this merger.

In Greek mythology, Andromeda is the daughter of the king of Aethiopia, Cepheus, and his wife, Cassiopeia. When Cassiopeia boasts that she is more beautiful than the Nereids, Poseidon sends the sea monster Cetus to ravage the coast of Aethiopia as divine punishment. Andromeda is chained to a rock as a sacrifice to sate the monster, but is saved from death by Perseus, who marries her and takes her to Greece to reign as his queen.

Her name means 'ruler of men', from meaning 'man, husband, human being', and 'I protect, rule over'.