Andromeda Galaxy. True-colour optical image from the Palomar Observatory Sky Survey of the Great Andromeda Galaxy (M31; NGC 224). It is 2.2 million light years from Earth in the constellation Andromeda. At 200 light years across it is the largest galaxy in the local group", a cluster of about 25 galaxies that includes our own, the Milky Way. Like the Milky Way, Andromeda is a spiral galaxy with a dense central bulge packed with millions of stars. Here, two small companion galaxies are also seen: the irregular galaxy NGC 205 (at right) and the elliptical galaxy NGC 221 (star-like object just below Andromeda's centre)."