The Crescent Nebula (NGC 6888 or Caldwell 27) is an emission nebula in the Cygnus constellation, 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 400,000 years ago. Wolf-Rayet stars are very hot, massive stars that are blowing off their outer layers. 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. The nebula is about 25 light years across and continues to expand. (Wikipedia and others)

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Dates:
August 5, September 4 and 5, 2010
Location:
Ft. Griffin State Historic Site, Texas
Telescope:
TEC 140 at f/7 980mm focal length
Mount:
Astro-Physics Mach1 guided by the ST-10XE internal and external guide chips
Camera:
SBIG ST-10XE at prime focus with CFW8 and Astronomik LRGB filters
Camera Control:
CCDSoft
Exposures:
L -190 mins at 5 min each; 1x1
Red - 60 mins with 12 exposures at 5 mins each; binned 2x2
Green - 60 mins with 12 exposures at 5 mins each; binned 2x2
Blue - 60 mins with 12 exposures at 5 mins each; binned 2x2
Exposure time:
L - 3 hrs 10 mins; R - 1 hr; G - 1 hr; B - 1 hr
Total Time:
6 hrs 10 mins
Processing:
CCDStack; Registar; Photoshop CS2; StarSpikes Pro