Messier 57 (M57), also known as the Ring Nebula, is a well-known planetary nebula located in the northern constellation Lyra. The Ring Nebula has an apparent magnitude of 8.8 and lies at an approximate distance of 2,300 light years from Earth. It has the designation NGC 6720 in the New General Catalogue.

Messier 57 lies south of Vega, the brightest star in Lyra and one of the stars that form the Summer Triangle, a prominent asterism found overhead in the summer sky. The nebula is easy to find as it is located roughly 40 percent of the distance from Sheliak, Beta Lyrae, to Sulafat, Gamma Lyrae.The nebula cannot be resolved in small binoculars and is best seen in 8-inch and larger telescopes. Even smaller telescopes will reveal the nebula’s ring shape, while medium-sized instruments will also show its interior hole.With a visual magnitude of 14.8, the nebula’s central white dwarf is a difficult target. The best time of year to observe M57 is in the summer months.Messier 57 occupies an area of 1.5 by 1 arc minutes. It is classified as a bipolar nebula as it has thick equatorial rings that extend its structure through its main axis of symmetry, which is seen at about 30° from Earth.The Ring Nebula is one of only four planetary nebulae listed in Messier’s catalogue, along with the Dumbbell Nebula (M27), the Little Dumbbell Nebula (M76), and the Owl Nebula (M97).Planetary nebulae are formed when a dying red giant star expels its shell of ionized gas to form the nebula, while the star itself becomes a white dwarf, a dense stellar remnant roughly the size of the Earth. The central star of the Ring Nebula ejected its outer layers 6,000 to 8,000 years ago and they have since expanded over an area about 1.3 light years in radius. The nebula is expanding at a rate of about 1 arc second per century, which corresponds to a velocity of 20 to 30 km/s.The nebula’s ring shape appears in different colours and the different layers seen in images are not equally bright. This is because they consist of different layers of the central star, or different elements at different temperatures. The outermost layer, which appears red in images, consists almost entirely of hydrogen. Elements that appear in different colours include doubly-ionized oxygen, molecular nitrogen, molecular sulphur, and helium.The central planetary nebula nucleus (PNN) has an estimated mass of 0.61 to 0.62 solar masses and a surface temperature of about 125,000 K. It is about 200 times more luminous than the Sun.The Ring Nebula was discovered by the French astronomer Antoine Darquier de Pellepoix in January 1779