The Andromeda Galaxy (also known as Messier 31 or M31) is a spiral galaxy approximately 2.5 million light-years away in the constellation Andromeda. It is the nearest spiral galaxy to our own Milky Way galaxy and is the largest galaxy of our Local Group, which also contains the Milky Way, the Triangulum Galaxy, and about 30 other smaller galaxies. It is estimated that M31 contains one trillion stars, at least twice the number of stars in our own Milky Way galaxy, which is estimated to be 200–400 billion.
The Andromeda Galaxy is one of the brightest Messier objects, making it visible to the naked eye from a dark site. Although only the brighter central region is visible to the naked eye, when photographed it appears more than six times as wide as the full Moon. This image is a 2-panel mosaic covering an area approximately 2° x 2°.
A 2-panel mosaic.
Each Panel: 16x300sec Subs, Darks, Flats and Bias.