M31, the Andromeda Galaxy, is the closest spiral galaxy to our galaxy, the Milky Way.

At about 2.5 million light years distant, M31 is approximately the same size as the Milky Way galaxy, with a diameter of about 100,000 light years.

Under dark skies M31 can be seen with the naked eye as a fuzzy patch in the constellation Andromeda. It is easily spotted from all but the most light-polluted sites with binoculars, and appears to be about three times the diameter of the full moon. In long exposure photos, the apparent extended size of the galaxy is seen to be close to three degrees, or six times the apparent size of the full moon.

Despite it's immense size and relative nearness to us, Andromeda's low surface brightness makes it difficult to pick up any texture visually. Through moderate sized amateur telescopes it appears to be a blurry oval, brighter in the center than on the edges. Larger amateur telescopes, under dark skies, begin to pick up some detail. Long photographic exposures can show the incredibly beautiful richness in texture that makes M31 a favorite target for amateur astrophotographers.

In this photo two companion galaxies of M31 can be seen. The irregular dwarf galaxy M32 is the bright blob above and to the left, and the elliptical galaxy M110 can be seen near the bottom of the photo.

This photo was made on 14-October-2007. The total exposure time is 20 minutes, at ISO 800. Another hour or two of exposure will be necessary to bring out all the detail possible with my equipment at my location.

Image details:

mount: Orion Atlas EQ-G
telescope: 203mm f/4.9 newtonian reflector
imaging focal length: 1000mm
imaging camera: Canon Digital Rebel XT
exposure time: 2 minutes, ISO 800
number of exposures: 10
guiding: automatic
guide scope: 80mm f/11.2 refractor
guide camera: Meade DSI-C
guiding software: PHD Guiding
image processing software: Iris, Adobe Photoshop CS2