The Milky Way, part of it at least, can be seen tonight under clear dark skies. It spreads across the eastern sky, from Cassiopeia in the north to Sagittarius in the south. The Milky Way is our home galaxy; we live on a planet orbiting a star about two-thirds of the way out from its center. Other galaxies surround ours, all bound together by gravity. We have satellite galaxies, most notably the Large and Small Magellanic Clouds. And there’s a bigger spiral galaxy about 2 and a half million light years away: its catalog number is M31, but we know it best as the Andromeda Galaxy. Now besides the Milky Way and M31, there are about 30 other, smaller galaxies in the immediate neighborhood (and by “immediate neighborhood,” we mean anything that’s within a million parsecs of here.) This cluster of galaxies is known as the Local Group. Most of them are fairly small and contain only a billion or so stars. M31 and the Milky Way are the Group’s gravitational “anchors”.