Stephan's Quintet is a
visual grouping of five galaxies of which four form the first compact galaxy group ever discovered. The group, visible in the constellation Pegasus, was discovered by Édouard Stephan in 1877 at the Marseille Observatory. The group is the most studied of all the compact galaxy
groups.The brightest member of the visual grouping (and the only non-member of the true group) is NGC 7320, which has extensive H II regions, identified as red blobs, where active star formation is occurring.