Crescent Nebula

Object Type: Emission Nebula
Scope: Orion APO 80mm; Exposure 60 minutes.

The Crescent Nebula (NGC 6888, Caldwell 27) is an emission nebula in Cygnus, about 5,000 light-years away. It is formed by the fast wind of the hot Wolf-Rayet star WR 136 slamming into the slower gas the star shed earlier, when it was a red giant around 400,000 years ago. The collision creates a glowing shell bracketed by shock waves; the inner shock heats the gas to X-ray temperatures. WR 136 is nearing the end of its life and is expected to explode as a supernova.