All of the other Messier objects we have talked about to this point are contained within our own Milky Way. The remaining class of Messier objects—galaxies—is on a completely different scale. Most galaxies in the Messier catalog are similar in size to our own galaxy, so they may contain billions of stars and scores of nebulae and star clusters of their own.

M31, the Andromeda galaxy, is very similar to our own galaxy, except that it's even bigger. It's the most distant object we can see in the night sky without binoculars—over two million light years away. If there was an astronomer living in the Andromeda galaxy, and he made his own catalog of fuzzy objects, it would not include any of the clusters or nebulae in our catalog, but it would have most of the same galaxies, with the exception of one additional galaxy, the Milky Way.

Not all galaxies look like ours, with it's flat disk and spiral arms. Elliptical galaxies, for instance, are shaped like giant balls. An interesting elliptical galaxy in the Messier catalog is M87 in the Virgo Cluster. This is the brontosaurus of elliptical galaxies, tipping the scales at 800 billion solar masses. At the heart of M87 is a gigantic black hole, with a mass of three billion suns.