NGC6888 Crescent Nebula

Photograph by

David Watson

About this image

The Crescent Nebula, catalogued as NGC 6888, Caldwell 27, and Sharpless 105, is an emission nebula in the constellation Cygnus, about 5000 light years away. It is formed by the fast stellar wind from the Wolf-Rayet star WR 136 (HD 192163) 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.