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 William 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.
Location: Stinger of Scorpius Observatory, Filiates, Thesprotia - Greece.
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Bortle Scale: Class 4
Imaging Telescope: William optics star 71 f/4.9
Equatorial Mount: Avalon linear fast reverse (Avalon Instruments)
Guide Scope : Skywatcher ed80 Black Diamond
Guide Camera:ZWO ASI290MM Mini (mono)
Main Camera: CCD Atik One 6.0 Monochrome
Filters: Astrodon Hydrogen Alpha 5nm
Exposures: 45X600sec for Hydrogen Alpha : (7.5 hours total)
: 42X600sec Oxygen iii : ( 7.0 hours total)
Image Calibration: 60 dark frames, 230 bias frames, 35 flat frames
Sensor temperature: -10°C
Image acquisition software: Artemis Capture
Telescope guiding software: PHD2
Processing software: Pixinsight - CCD stack - Photoshop CS6
Acquisition dates: 05/06/2021 - 29/06/2021 (H-Alpha Filter)
12/07/2021 - 14/07/2021 (Oiii filter)
Total exposure : 14.5 hours