Andromeda Galaxy Andromeda Galaxy The Andromeda Galaxy (), also known as Messier 31, M31, or NGC 224, is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth, and the nearest major galaxy to the Milky Way. Its name stems from the area of the sky in which it appears, the constellation of Andromeda. The 2006 observations by the Spitzer Space Telescope revealed that the Andromeda Galaxy contains approximately one trillion stars, more than twice the number of the Milky Way's estimated 200 to 400 billion stars. The Andromeda Galaxy's mass is estimated to be around 1.76 times that of the
Triangulum Galaxy in the night sky. It also has an H-II nucleus. The galaxy gets its name from the constellation Triangulum, which is where it can be spotted. The Triangulum Galaxy is sometimes informally referred to as the "Pinwheel Galaxy" by some amateur astronomy references and in some public outreach websites. However, the SIMBAD Astronomical Database, a professional astronomy database that contains formal designations for astronomical objects, indicates that the name Pinwheel Galaxy is used to refer to Messier 101, and several other amateur astronomy resources and other public outreach websites also identify Messier 101 by that name. Under exceptionally good viewing