Ringnebel

Ringnebel refers to the Ring Nebula, known in English as M57 or NGC 6720. It is a planetary nebula located in the northern constellation Lyra and is among the best-known and most studied examples of this class. Its prominent, circular appearance has made it a common target for both amateur and professional observers.

The nebula forms from the outer layers ejected by a star similar in mass to the Sun as it leaves the asymptotic giant branch. The remaining stellar core becomes a very hot white dwarf, whose ultraviolet radiation ionizes the expanding gas. The bright ring arises from a limb-brightened shell or torus of gas, with fainter material and knots present in a surrounding halo. Emission lines from ionized hydrogen and oxygen dominate the visible spectrum.

Distance estimates place Ringnebel at about 2,000 light-years from Earth, and it spans roughly one light-year in diameter. Its apparent size is a few arcminutes across. The expansion velocity of the nebular gas is typically around 20–30 km/s, implying an age since ejection of several thousand years. The central star has a temperature on the order of 100,000–150,000 kelvin.

Discovery and significance: Ringnebel was described independently in 1779 by Antoine Darquier de Pellepoix and by Charles Messier, who added it to his catalog as M57. It serves as a standard example for studying late stellar evolution, photoionization, and chemical abundances in nebulae. High-resolution imaging, including from the Hubble Space Telescope, reveals a clumpy, knotty structure within the ring.

Notes: Ringnebel is the German name for the Ring Nebula; in English literature it is widely referred to as Ring Nebula.