M57, Ring Nebula

The Ring Nebula (also catalogued as Messier 57, M57 or NGC 6720) is a planetary nebula in the northern constellation of Lyra. Such objects are formed when a shell of ionized gas is expelled into the surrounding interstellar medium by a star at the end of its asymptotic giant branch phase, in the last stages of its evolution before becoming a white dwarf. The nebula was found by Charles Messier in 1799 while he was looking for comets.