The Milky Way

Our whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, the Milky Way, a spiral disk of 200 billion stars and their planets, and thousands of clusters and nebulae.  All these objects orbit their common center of mass called the Galactic Center. Our Sun is one of the 200 billion stars of the milky way and is located roughly 24,000 light years from the Galactic Center.

As a galaxy, the Milky Way is actually a giant, as its mass is probably between 750 billion and one trillion solar masses, and its diameter is about 100,000 light years. The Milky Way Galaxy belongs to the Local Group of galaxies, a small group of 3 large and over 30 small galaxies, and is the second largest (after the Andromeda Galaxy/M31) of this group. Andromeda is also a spiral galaxy like the Milky Way but is 4 times as massive and is 2.9 million light years away.  Andromeda is the nearest large galaxy, but a number of faint galaxies are much closer: Many of the dwarf Local Group members are satellites or companions of the Milky Way. The closest of all is the Sagittarius Dwarf Elliptical Galaxy (SagDEG) at about 80,000 light years from us and some 50,000 light years from the Galactic Center, followed by the more conspicuous Large and Small Megallanic Clouds at 179,000 and 210,000 light years, respectively.