The spiral galaxy nearest to our own, and the largest member of the Local Group; also called M31 and NGC 224. It lies 2.5 million l.y. away and is visible to the naked eye as an elongated patch of light of total magnitude 3.4 in the constellation Andromeda. The Andromeda Galaxy has two arms and is classified as an Sb spiral. Its total mass is over 1000 billion solar masses, almost twice as massive as our own Galaxy. On long-exposure photographs it can be traced across over 4° of sky, corresponding to a diameter of about 150 000 l.y. It has around 600 globular clusters, over three times as many as our own Galaxy. There are two close dwarf elliptical companion galaxies, both of 8th magnitude: M32 (NGC 221), and NGC 205 (sometimes known as M110), plus more than ten dwarf spheroidal systems.

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