The Crescent Nebula (NGC 6888) is an emission nebula in the constellation Cygnus, about 5,000 light-years from Earth. It is the result of the collision and compression of the fast stellar wind of the Wolf-Rayet star WR 136 (at the center of the nebula) with the slower stellar wind gas blown off by the star when it was still a red giant 250,000 to 400,000 years ago. The result of the collision is a shell and two shock waves, one moving outward and one moving inward. The inward shock wave heated the stellar wind to X-ray temperatures. The Crescent Nebula is a small object, about 18′x12′ in visual size, and has a brightness of +7.4 magnitude.