Crescent Nebula (also known as NGC 6888, Caldwell 27, 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 250,000to 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 moving shock wave heats the stellar wind to X-ray-emitting temperatures. [Description from wikipedia] Ha: 20 x 30m (5nm) OIII: 16 x 30m (3nm) total exposure time: 18 hours. Main Camera: QSI 583 WSG Guide Camera: SXV Lodestar (on OAG) Mount: Astro-Physics Mach 1 Scope: Celestron Edge HD 8" (FL: 2032mm) Adaptive Optics Unit: SXV-AO-LF Image Aquisition software MaximDL Registed, Calibrated and Stacked in MaximDL Post Processed with PixInsight 1.8 and Photoshop CS6

[Description adapted from NASA APOD: the Crab is now known to be a supernova remnant, an expanding cloud of debris from the explosion of a massive star. The violent birth of the Crab was witnessed by astronomers in the year 1054. Roughly 10 light-years across today, the nebula is still expanding at a rate of over 1,000 kilometers per second] This is a bicolor-rendition in the same style as NGC6888 (linked below in the comments). I have mapped Ha to Red, OIII to blue and created a synthetic green channel mixing the two (15% OIII + 85% Ha). Ha: 20 x 30m (5nm) OIII: 20 x 30m (3nm) total exposure time: 20 hours. Main Camera: QSI 583 WSG Guide Camera: SXV Lodestar (on OAG) Mount: Astro-Physics Mach 1 Scope: Celestron Edge HD 8" (FL: 2032mm) Adaptive Optics Unit: SXV-AO-LF Image Aquisition software MaximDL Registed, Calibrated and Stacked in MaximDL Post Processed with PixInsight 1.8 and Photoshop CS6