QuintetCredit: © Subaru Telescope, National Astronomical Observatory of Japan (NAOJ)Thursday, December 8, 2011: Stephan’s Quintet, in the constellation Pegasus, consists of five galaxies, although one lies closer than the others. Japan’s Subaru Telescope shows two views of the grouping using different filters to distinguish the recession velocity of each object, the speed at which the object movies away from the observer. The image on the left shows the galaxies filtered for a recession velocity of 0, while the one on the right shows them filtered for a recession velocity of 4,200 miles per second. The contrasting images show that NGC7320 (lower left) is closer than the other galaxies.

— Tom Chao