M 31, the "Andromeda Galaxy", is the large galaxy nearest to
our own (estimates range from 2.4-2.9 million light years away).
It is, like our Milky Way, a spiral galaxy, though at more than
200,000 light year across it is more than twice as large as the
Milky Way. It is easily visible to the naked eye, appearing as a
fuzzy smudge of light. The eye can see only the bright central
region, but the full width of the galaxy is as long as 6 full
moons in the sky. M 31, unlike most galaxies, is approaching the
Milky Way (at 100 kilometers / second). Our galaxy and M 31 will meet
someday, and after a very long dance will merge into one huge galaxy.
But that day is billions of years away. There are two much smaller
elliptical companion galaxies visible in this image: M 32 above, and
M 110 below.

Image data:
Camera: SBIG STL-11000
Telescope: Takahashi FSQ 106n
Exposure: Luminance = 135 minutes (9 minutes x 15)
Color: Red = 60 minutes (15 minutes x 4)
Green = 36 minutes (9 minutes x 4)
Blue = 72 minutes (18 minutes x 4)