15 December 2012
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth. It is the nearest spiral galaxy to our Milky Way galaxy, but not the closest galaxy overall. The Andromeda Galaxy (click on above image to enlarge) is the largest galaxy of the Local Group, which also contains the Milky Way and about 30 smaller galaxies. Although the largest, the Andromeda Galaxy may not be the most massive, as recent findings suggest that the Milky Way contains more dark matter and could be the most massive in the group.
The two galaxies are expected to collide in 3.75 billion years, eventually merging to form a giant elliptical galaxy.
Note ~ a light-year is a unit of length approximately equal to 6 trillion miles.