Andromeda (M31 or Messier 31, NGC 224)
is a spiral galaxy about
two and a half million light-years away.
It is within the Local Group and is the nearest galaxy
to the Milky Way that is similar: the Local Group contains
one more somewhat similar spiral galaxy that is substantially smaller,
and numerous smaller dwarfsatellite galaxies.
Andromeda is somewhat larger than the Milky Way, with
on the order of a trillion stars.
Andromeda was observed before the current concept of a galaxy
was established, at the time, known as the Great Andromeda Nebula.
Characteristics: