M57 - RING NEBULA

The Ring Nebula (M57, NGC 6720) is one of the most famous and frequently observed planetary nebulae in the sky, located approximately 2,300 light-years from Earth in the constellation Lyra. It was discovered independently by Antoine Darquier de Pellepoix and Charles Messier in January 1779. The nebula is the expelled outer layers of a sun-like star that exhausted its nuclear fuel and shed its atmosphere into space, leaving behind a tiny, extremely hot white dwarf star at the center. This central star, with a surface temperature of about 120,000 Kelvin, ionizes the surrounding gas and causes it to glow in characteristic colors: the inner region appears blue-green from doubly ionized oxygen, while the outer ring glows red from hydrogen-alpha emission. The Ring Nebula has an apparent size of about 1.4 by 1.0 arcminutes, corresponding to a physical diameter of roughly 1.3 light-years. Despite its name suggesting a simple ring shape, deep imaging and Hubble Space Telescope observations have revealed that M57 is actually a barrel-shaped or cylindrical structure that we happen to view nearly pole-on, giving it the appearance of a ring. The nebula also possesses faint outer halos that extend well beyond the bright ring, evidence of earlier mass-loss episodes. M57 is easily found between the stars Sheliak (Beta Lyrae) and Sulafat (Gamma Lyrae). Even a small telescope will show the characteristic ring shape, though the central star requires at least a 12-inch telescope and excellent conditions to glimpse visually. The Ring Nebula is one of the finest examples of a planetary nebula and serves as an important object for understanding the final stages of stellar evolution for low- and intermediate-mass stars.

M57 is approximately 1.3 light-years in diameter with a central white dwarf star at 120,000 Kelvin, located about 2,300 light-years from Earth.