NGC 6888, or 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 (HD 192163) colliding with and energizing the slower moving wind ejected by the star when it became a red giant around 250,000 to 400,000 years ago.

Image details:
Telescope: TS 90/600 triplet with 2.5" TS flattener
Mount: Skywatcher HEQ5-Synscan
Camera: Atik one 6.0
Exposure: 66 * 300sec Ha, 40 * 300sec OIII, 13 * 300sec RGB
Software: PixInsight, PHD
Calibrationfiles: Dark:No, Bias:Yes, Flat:Yes

(c) All photos by Ruud de Vries