M100 is located in the constellation Coma Berenices.  It is approximately 55 million light years away and has a diameter of about 155,000 light years.  Note the numerous other faint galaxies in the image and the smaller galaxy to the left.  This galaxy is known as NGC 4312.
Image was taken from Lubbock, TX on the night of February 16, 2013.  It's a 10 minute exposure with a total exposure time of 130 minutes.