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June 13, 2010

The old saying that a picture is worth a thousand words is especially appropriate for the spiral galaxy known as M101. It's been the subject of some of the most famous astronomical images in history.

The galaxy is a near-perfect spiral. It spans about 170,000 light-years, so it's a good bit bigger than our home spiral galaxy, the Milky Way. And it contains a lot more stars than the Milky Way -- a trillion or more.

The galaxy is a popular portrait subject because it's fairly close, so we see it clearly, and because it's turned face-on to us, so we have a perfect view of its spiral structure. That structure earned M101 its nickname: the Pinwheel galaxy.

M101 was the first galaxy ever seen as a spiral. In 1851, a British amateur astronomer, Lord Rosse, drew M101 after viewing it through a giant telescope he'd designed and built. It was the first picture ever to show a galaxy's full spiral structure. At the time, though, no one knew its true nature -- most astronomers thought it was a whirl of matter inside the Milky Way.

And a few years ago, M101 was the subject of Hubble Space Telescope's largest galaxy picture yet -- a monster of almost 200 megapixels. It shows not just the spiral arms, the bright central bulge, and the galaxy's star clusters -- it even shows individual stars.

M101 is near the tip of the Big Dipper's handle. It's so far away, though, that you need a telescope to see this picture-perfect galaxy.

Script by Damond Benningfield, Copyright 2010

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