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Andromeda galaxy (M31), optical image. The galaxy comprises a central nucleus surrounded by spiral arms. The nucleus appears more yellow than the spiral arms as it contains a higher proportion of dust and older, redder stars. Two small satellite galaxies are associated with Andromeda, M32 (NGC 221), the fuzzy blob at lower right, and M110 (NGC 205), the bright star-like point immediately left of Andromeda's nucleus. The Andromeda galaxy is the closest major galaxy to our own Milky Way, lying just over two million light years away. It is also about half as large again as the Milky Way, with a span of over 150,000 light years. The galaxy takes its name from the constellation Andromeda, in which is it found. (KEYSTONE/SCIENCE PHOTO LIBRARY/ROBERT GENDLER)