M31 - the "Andromeda Galaxy" - is the nearest large galaxy next to our Milky Way. The distance between them is 2.2 mill. light-years, and they are the biggest members of the "Local Group" of galaxies, bound together gravitationally. Two small satellite galaxies to M31 are also visible on the image, M110 to the lower right, and M32 near the upper left edge of the galaxy.
Under dark and transparent conditions M31 can be seen as a fuzzy patch with the naked eyes.