The famously named "Ring Nebula" (also catalogued as Messier 57, M57 or NGC 6720) appears in the northern constellation of Lyra and is located in the Carina–Sagittarius Arm. It is one of the most prominent examples of a planetary nebula, the gaseous remains of a red giant star that has ended its life by expelling its material into the surrounding interstellar medium.
This nebula was discovered by Antoine Darquier de Pellepoix in January, 1779, who reported that it was "...as large as Jupiter and resembles a planet which is fading." Later the same month, Charles Messier independently found the same nebula while searching for comets. It was then entered into his catalogue as the 57th object. Messier and William Herschel also speculated that the nebula was formed by multiple faint stars that were unable to resolve with his telescope.
In 1800, Count Friedrich von Hahn discovered the faint central star in the heart of the nebula. In 1864, William Huggins examined the spectra of multiple nebulae, discovering that some of these objects, including M57, displayed the spectra of bright emission lines characteristic of fluorescing glowing gases. Huggins concluded that most planetary nebulae were not composed of unresolved stars, as had been previously suspected, but were nebulosities.
M57 is located south of the bright star Vega, which forms the northwestern vertex of the Summer Triangle asterism. It lies midway between β and γ Lyrae, making it an easy target for astronomers.
Release date: Nov 15, 2011