• Source: Crescent Nebula

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.
The Crescent Nebula is a rather small object located about 2 degrees Southwest of Sadr. While considered bright by astronomical imaging standards, visually it is relatively faint. For most telescopes it requires a UHC or OIII filter to see. Under favorable circumstances a telescope as small as 8 cm (with filter) can see its nebulosity. Larger telescopes (20 cm or more) reveal the crescent or a Euro sign shape which makes some to call it the "Euro sign nebula".

























See also


Cygnus Bubble




References






External links



"Crescent". National Optical Astronomy Observatory. Archived from the original on 2007-08-30. Retrieved 2005-01-08.
"Crescent Nebula: Live Fast, Blow Hard and Die Young". Chandra X-Ray Observatory. 14 October 2003.

Crescent Nebula on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
Nemiroff, R.; Bonnell, J., eds. (11 November 2007). "NGC 6888: The Crescent Nebula". Astronomy Picture of the Day. NASA. Retrieved 25 March 2018.

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