Portal:Astronomy/Picture/25 July 2005
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![](http://upload.wikimedia.org/wikipedia/commons/thumb/5/52/M101-PIA04630.jpg/300px-M101-PIA04630.jpg)
M101, also known as the pinwheel galaxy, is a spiral galaxy in Ursa Major, and is the largest member of a galaxy cluster called the M101 group. It was one of the first galaxies found to have a spiral structure.