Ring Nebula

The Ring Nebula ( Messier 57 or NGC also referred 6720 ) is a planetary nebula in the constellation Lyra.

The nebula is the remnant of a star that has shed its outer shell of gas around 20,000 years ago. The shell of gas expands at a speed of 19 km / s and currently has an apparent diameter of about 118 arc seconds, which means an absolute diameter of about 1.3 light years at a distance of 2,300 light years. In a telescope the nebula ring, which is why he is often referred to as the Ring Nebula in Lyra. In fact, the visible shell of gas resembles a torus. In the center of the nebula is a white dwarf star with a surface temperature of about 70,000 ° C and an apparent magnitude of 15.8 is like.

M 57 can be relatively easily found, as it β approximately in the middle of the line connecting the stars and γ Lyrae is.

Discovery

M 57 was discovered in 1779 by Antoine Darquier in the observation of a comet. In the same year Charles Messier took him into his catalog.

Darquier compared the appearance of the nebula with a planet, what the astronomer Friedrich Wilhelm Herschel prompted to call this type of fog as a planetary nebula.

Appearance

M 57 can be seen already in a small telescope of 10 cm aperture as misty " smoke ring ". This, however, is relatively small, so that higher magnifications (> 100) are appropriate. In telescopes from 25 cm aperture structures are visible at higher magnification in the ring.

The central star has a visual magnitude of 15.8 m but extremely faint. To observe it, one needs a telescope of at least 20 cm opening.