The Andromeda nebula

The Andromeda nebula

Fig. 16.2 . At one time, spiral nebulae like Andromeda were thought to be young stars enveloped by protoplanetary material. We now know that the Andromeda nebula is the nearest large galaxy to our own, located at a distance of about 2.6 million light-years. Both the Andromeda nebula and our Galaxy are spiral galaxies with similar sizes and total masses, containing roughly a hundred billion, or 1011, visible stars. This photograph was taken in visible light with the 5.0-meter (200-inch) telescope at the Palomar Observatory near Pasadena, California. The two, smaller elliptical galaxies are at about the same distance as M 31, but with only about one hundredth of its mass. (Courtesy of the Palomar Observatory.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University