Time: 01:08UT 2021-05-25 Exp. R: 12x5min G: 11x5min B: 10x5min
Tel SPA-2: Officina Stellare 700 RC 0.7m f/6.0 & FLI PL16803 CCD 0.86"/pix
Odd Trondal Obs.code X02.

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. It is a rather faint object located about 2 degrees SW of Sadr. For most telescopes it requires a UHC or OIII filter to see. Under favorable circumstances in a telescope as small as 8 cm ...