Decorative print of an image taken by the Hubble Telescope. © NASA
Stephans Quintet is a group of five galaxies in the constellation Pegasus, discovered on 22 September 1877 by French astronomer Édouard Jean-Marie Stephan.
The galaxy group consists of the galaxies NGC 7317, NGC 7318A, NGC 7318B, NGC 7319 and NGC 7320. The galaxies NGC 7317 to NGC 7319 form a spatially close, interacting system about 300 million light-years away. Due to mutual gravitational interaction, the spiral arms of the galaxies are irregularly shaped.
NGC 7320 was originally included by Stephan in Stephan's Quintet, but due to its significantly lower heliocentric radial relative velocity (~ 800 km/s compared to ~ 6500–7000 km/s for the other galaxies), this galaxy is a foreground galaxy only 35 million light-years away, which only coincides with Stephan's Quintet due to projection. Instead, NGC 7320C is now added to the quintet, so that there are still five galaxies.
The galaxies of Stephan's Quintet have a brightness of about 13 mag. To observe them, you need a telescope with at least 20 cm aperture.
