M57: The Ring Nebula.

It looked like a ring on the sky. Hundreds of years ago astronomers noticed a nebula with a most unusual shape. 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 . The Ring Nebula lies about 4,000 light years away, and is roughly 500 times the diameter of our Solar System . In this recent picture by the Hubble Space Telescope , dust filaments and globules are visible far from the central star. This helps indicate that the Ring Nebula is not spherical, but cylindrical .