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. It is the nearest major
galaxy to the
Milky Way and was often referred to as the
Great Andromeda Nebula in older texts. It received its name from the area of the sky in which it appears, the
constellation of Andromeda, which was named after the mythological princess
Andromeda. Being approximately 220,000 light years across, it is the largest galaxy of the
Local Group, which also contains the Milky Way, the
Triangulum Galaxy, and about 44 other smaller galaxies.