The Andromeda Galaxy (also known as Messier 31 or M31) is a spiral galaxy. It is the closest major galaxy to our own Milky Way Galaxy. Spiral galaxies are characterized by a central bulge, a disk of stars and gas, and spiral arms that extend from the center. The Andromeda Galaxy is the largest member of the Local Group of galaxies, which includes the Milky Way Galaxy and about 50 other smaller galaxies.