The Ring Nebula (also catalogued as Messier 57, M57 and NGC 6720) is a planetary nebula in the northern constellation of Lyra. Such a nebula is formed when a star, during the last stages of its evolution before becoming a white dwarf, expels a vast luminous envelope of ionized gas into the surrounding interstellar space.
M57 is 2,570 light-years from Earth. It has a visual magnitude of 8.8 and a dimmer photographic magnitude, of 9.7. Photographs taken over a period of 50 years show the rate of nebula expansion is roughly 1 arcsecond per century, which corresponds to spectroscopic observations as 20–30 km s−1. M57 is illuminated by a central white dwarf or planetary nebula nucleus (PNN) of 15.75v visual magnitude.