This Messier Object, also known as NGC 5194, is a face-on Seyfert grand design spiral galaxy located 25 million light years away in the constellation of Canes Venatici at a declination of +47 degrees.  It is a magnitude 8.4 galaxy which spans 10 arc-minutes in our apparent view.  This corresponds to a diameter of 80,000 light years.  It is the 14th brightest galaxy in the sky.

The Whirlpool Galaxy is one of my favorite night sky objects. Viewed face-on from earth, the graceful, symmetric arms contain flowing dark lanes, blue star clusters and pink hydrogen star-forming regions.  VV rows are seen in the grand design spiral arms

The companion galaxy slightly below and behind M51 is NGC 5195.  Numerous encounter theories have been proposed for those 2 objects.  One of my favorite proposed sequences is this one, from the groundbreaking galaxy encounter work by Toomre and Toomre.  The bottom row is the view of these objects from earth, the top row is the view from above them (for better clarity).  Time goes from left to right.  The bottom right image is as we see it from earth today:


Their work indicates that we are not seeing a bridge between these 2 galaxies, as it may appear from the image.  We are simply seeing M51 in front of NGC 5195.  This is best seen in the "from above" view in the upper right image.  The smaller galaxy has passed M51 from top right to bottom left, just grazing the left edge of M51. The smaller galaxy has now passed behind M51, but the gravitation influences are still apparent in the distorted star patterns and the brighter than normal blue and pink regions of M51. The two galaxies may merge in the future after several more "dances".

My favorite part of the image is the wispy outlying star cloud of the smaller galaxy NGC 5195, on the left.  I also like how the left side of the dark lane of M51 overlaps with the core of NGC 5195.  That core provides a light background which accentuates the M51 dark lane.