Caldwell 27, also known as NGC 6888 and the "Crescent Nebula" is an emission nebula in the constellation of Cygnus. It lies at a distance of ~5,000 light-years.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.This image comprises 8 x Ha, OIII and SII (200 seconds each), 0.5m f/2.9 ASA Astrograph with FLI ML3200 camera at an altitude of 75 degrees over two nights, 29 June and 8 July 2017. The images were processed using the CFHT convention, Ha-OIII-SII mapped to RGB. The field of view is 34’ x 23’.
Hills Observatory: 1 January 2013 to 19 January 2019