M57: The Ring Nebula . ... Hubble Heritage Team ( STScI / AURA ), NASA Explanation: It looks like a ring on the sky. ... Now known as M57 or NGC 6720, the gas cloud became popularly known as the Ring Nebula . It is now known to be a planetary nebula, a gas cloud emitted at the end of a Sun-like star's existence. As one of the brightest planetary nebula on the sky, the Ring Nebula can be seen with a small telescope in the constellation of Lyra . ... NASA Official: Jay Norris. ...