APOD 2.1

The Andromeda Galaxy, seen in the visible spectrum.

The Andromeda Galaxy, seen in the ultraviolet spectrum.

Here we see M31, or the Andromeda Galaxy, with pictures comparing the visible spectrum and the ultraviolet spectrum. The ultraviolet image, on the bottom, reveals many individual stars that can't be seen in the visible spectrum. The galaxy is on a collision course with the Milky Way, and the theoretical collision might occur in 4.5 billion years.