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March 2002

M101: The Pinwheel Galaxy

M101 is a fine example of a spiral galaxy - a system of over 100 billion stars, along with lots of hydrogen gas, molecular gas, and interstellar dust. Our own Milky Way might look very much like M101 if we could view it from above ("face-on"). Our Sun would sit about 2/3 of the way from the bright center to the edge of this image. The area shown here is about 100,000 light years across.

M101 lies about 25 million light-years from us, in the constellation of Ursa Major. It is only faintly visible through binoculars on a dark moonless night. In this CCD image, the nucleus appears yellowish as it is made of of millions of ordinary stars like our sun and cooler. The spiral arms appear bluer - they contain newly made massive stars that are much hotter than our sun. The colorful gas clouds surround clusters of young stars, whose energy causes the gas to glow in the light of hydrogen (red) and oxygen (green).