Stephan's Quintet (NGC 7317, NGC 7318A, NGC 7318B, NGC 7319, NGC 7320)

Stephan's Quintet, as its name implies, is a group of five galaxies (NGC7317, 7318A, 7318B, 7319 and 7320) in the constellation Pegasus. This unusual system has often been used as proof that the redshift is not truly a distance indicator, which would completely overturn current cosmology, because although four of the galaxies have similar, large redshifts, the fifth (NGC7320), although apparently a member of the group, shows a much smaller redshift. Conventional theory states that the low-redshift galaxy is in a nearby group (the NGC7331 group) and by coincidence appears on the sky projected against a distant background group. Opponents point to debris and tails around the low-redshift galaxy, suggesting that it is interacting with the high-redshift systems, which would require that all five galaxies be at the same physical location in space. See also our color picture from the 0.9-meter.