... Careful inspection of the full field of view for this sharp composite image reveals a surprising number of galaxies both near and far toward the constellation Ursa Major. ... It's the blue wisp near the bottom that's the remnant of a tremendous recent supernova explosion. ... Of course, the nebula is itself a star-forming region, but the stars that appear and disappear here include background and foreground stars that by chance lie along the same line of sight. The Matter of the Bullet Cluster . ...