The Crescent Nebula (also known as NGC 6888, Caldwell 27, Sharpless 105) is an emission nebula in the constellation Cygnus, about 5000 light-years away from Earth. 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. 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 light sub-frames were acquired over the last two nights (7/6-7) and represents just under 2 hours of Hydrogen-alpha and 4 hours of Oxygen-III narrowband data. It is the first image that I have successfully created with 10 minute subs (600 sec) and also the first light on my new field flattener. I believe the reason I was able to pull off longer subframes has entirely to do with balance on the mount – autoguider and OTA parallel and centered over frame versus the dual-saddle side-by-side configuration I end up having to use when I use camera lenses. This is my first attempt at the Crescent and despite some bleary-eyed, late-night, rushed bi-color processing, I think it turned out alright. Practice helps.