M101 is a relatively large galaxy compared to the Milky Way. With a diameter of 170,000 light-years it is nearly twice the size of the Milky Way. It has a disk mass on the order of 100 billion solar masses, along with a small bulge of about 3 billion solar masses. On photographs M101 can be seen to be asymmetrical on one side. It is thought that in the recent past (speaking in galactic terms) M101 underwent a near collision with another galaxy and the associated gravitational tidal forces caused the asymmetry. This image, taken on April 21, was exposed for a total of 3 hours using a Takahashi FSQ-106 Refractor and an SBIG STL-11000 CCD camera. Click on the image above to see it at full resolution. Look for the small galaxy to the left of M101, and the edge on galaxy to the right.