Andromeda galaxy. Infrared Spitzer Space Telescope image of the Andromeda galaxy (M31). Different colours show different temperatures of galactic dust. The hottest dust is white, then blue, through yellow and orange to red, the coolest dust. Seen here is the intricate structure of the spiral arms and an unexpected hole (lower right) in the galaxy's disk. The Andromeda galaxy measures 150,000 light years across and is located in the constellation Andromeda, around 2.5 million light years from Earth. It is the closest major galaxy to the Milky Way.