The Andromeda Galaxy (M31) is one of the nearest galaxies in our local neighbourhood, and is visible to the naked eye from a dark site. Being so near, it also has a very large apparent size: the width of 6 full moons. The bright blue patch near the top left is designated NGC 206, and is a very large open cluster within M31. It has two satellite galaxies, M32 near the top left, and M110 near the bottom left.
The HII regions have been emphasized by layering an H-alpha exposure into the red and luminance channels.
This image was updated 18-October-2008. I gathered 3h45m worth of added luminance and blended with the original image, which helped me bring out some better contrast and detail in the central region.
View in World Wide Telescope (Requires install).