A large-scale image of M31, the Andromeda Galaxy, emphasizing the various colors of regions with different kinds of stars, by using different choices for the colors assigned to black-and-white images taken at various wavelengths. The small elliptical above M31 is M32, while the larger, more elongated elliptical below it is M110 (also called NGC205).
     The bright blue stars lighting up the outer parts of the galaxy were recently formed from clouds of gas and dust (visible elsewhere in the image, as dark lanes superimposed on the starry background) in the galaxy's spiral arms. Ultraviolet and infrared images of the galaxy reveal that the star-forming regions form concentric circles around the galaxy, as if a bullseye; and it is thought that perhaps that is just what they are -- the result of M32 passing right through the center of M31, a few tens of millions of years ago. (Robert Gendler, apod051222)