The Crescent Nebula  is an emission nebula in the constellation Cygnus, about 5000 light-years away.  It was discovered by Friedrich Wilhelm Herschel in 1792. It is formed by the fast stellar wind from the Wolf-Rayet star WR 136 colliding with and energizing the slower moving wind ejected by the star when it became a red giant around 250,000 years ago. The result of the collision is a shell and two shock waves, one moving outward and one moving inward. The inward moving shock wave heats the stellar wind to X-ray-emitting temperatures. Desktop Version Crescent Nebula (RGBHa) 68min Old Version (Modified DSLR) 60min