This beautiful ring nebula is actually an expanding shell of gas thrown off explosively by a dying star, which is barely visible at the center of the ring. The gasses forming the ring glow (similar to a fluorescent light) as a result of ultraviolet radiation from the central star. The different colors of the nebula result from the diverse physical conditions of the gas where the emission originates. For example, the center of the ring appears blue from emissions of helium close to the star, because helium requires higher-energy photons to ionize than hydrogen or oxygen, and the conditions for emission by helium primarily occur near the star. The nebula shines at magnitude 8.8, while the central star is a faint magnitude 15.29. It is located about 1500 light-years away. The nebula is approximately 500 times the size of our solar system. The gasses of the nebula are expanding at a radial velocity of about 12 miles per second.
French astronomer Antoine Darquier de Pellepoix is credited with discovering the ring nebula in 1779. M57 was the first planetary nebula found, and it was the second planetary nebula added to the Messier catalog. The ring nebula is a so-called "planetary nebula", although it has nothing to do with a planet. Nebula of this type were named planetary nebula in the 18th century because these nebula resembled the disk of a planet in the telescopes of the time, and the name has stuck to this day.
This is an RGB composite CCD image taken with an SBIG ST-8E CCD on a Takahashi Mewlon 210 telescope at prime focus. The exposures were made from my backyard in Scottsdale, Arizona.
M57 (NGC 6720)
Constellation: Lyra
RA: 18h 53m 43.5s Dec: +33d 01' 56"
May 14, 2005
Image by Sid Leach
Scottsdale, Arizona.
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