M101: A striking example of the spiral galaxy (like our galaxy, the Milky Way) is M101, shown above, whose relatively close distance of about 22 million light years allow it to be studied in some detail. It is located in Ursa Major (of which the Big Dipper is a part), near the tip of the handle of the Big Dipper. Recent evidence indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass and condensed gas which continue to circle the galaxy. These waves compress existing gas and cause star formation. One result is that M101 has several extremely bright star-forming regions (called HII regions) spread across its spiral arms (which appear as pinkish blobs in the picture). M101 is so large that its immense gravity distorts smaller nearby galaxies.
Copyright Mark de Regt, 2001