Crescent Nebula
{{Short description|Emission nebula in the constellation Cygnus}}{{More citations needed|date=May 2024}}{{Infobox nebula
| name = Crescent Nebula
| image = NGC 6888.png
| caption = The Crescent Nebula, captured with a color camera, narrowband filter, and high-speed amateur telescope
| type = Emission
| epoch = J2000.0
| ra = {{RA|20|12|7}}{{cite simbad
| title=NGC 6888
| access-date=2007-04-23}}
| dist_ly = 5,000
| appmag_v = +7.4
| size_v = 18′ × 12′
| constellation = Cygnus
| radius_ly =
| absmag_v =
| notes =
| names = NGC 6888, Sharpless 105, Caldwell 27
}}
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.{{cite web |url=http://www.ngcicproject.org/ngcicdb.asp |title=NGC 6888 |work=The NGC/IC Project |last1=Erdmann |first1=Robert |url-status=dead |archive-url=https://web.archive.org/web/20120520010558/http://www.ngcicproject.org/ngcicdb.asp |archive-date=2012-05-20 }} 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{{cite web|url=http://jumk.de/astronomie/big-stars/wr-136.shtml |title=WR 136 |access-date=25 March 2018 |website=jumk.de}} to 400,000{{citation needed|date=January 2013}} 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.
Visibility
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 call it the "Euro sign nebula".{{cn|date=April 2025}}
Gallery
File:NGC 6888 HOO By Don Christopher Deaver.jpg|alt=Crescent Nebula NGC 68888 Imaged by Don Christopher Deaver|NGC 6888 in Hydrogen and Oxygen Light. HOO Palette. Imaged by Don Christopher Deaver
File:Crescent Nebula, Hydrogen alpha and Oxygen III by Stephan Hamel.jpg|Crescent Nebula in H-alpha and OIII. Imaged with a 715mm focal length telescope. The hydrogen gas is red. The oxygen is blue.
File:Crescent Nebula in H-alpha.jpg|Image of NGC 6888 using H-alpha filter.
File:NGC 6888 (Crescent Nebula) bicolor.jpg|Picture of NGC 6888 captured in narrowband by amateur astronomer Luca Moretti
File:NGC 6888, the Crescent Nebula in Cygnus, imaged by amateur astronomer Patrick Hsieh.jpg|NGC 6888 imaged in 3 nm hydrogen-alpha and oxygen-III narrowband at 2800mm focal length by amateur astronomer Patrick Hsieh.
File:C27 - Crescent Nebula.jpg|Crescent Nebula (Caldwell27) was captured by David Rousseau from an urban location in Québec, Canada, using Ha and OIII narrowband filters.
File:CrescentBicolorHunterWilson.jpg|The Crescent Nebula, as taken by an amateur astronomer
See also
References
{{reflist}}
External links
{{commons category}}
- {{cite web|url=http://www.noao.edu/image_gallery/html/im0834.html|title=Crescent|publisher=National Optical Astronomy Observatory|access-date=2005-01-08|archive-date=2007-08-30|archive-url=https://web.archive.org/web/20070830193539/http://www.noao.edu/image_gallery/html/im0834.html|url-status=dead}}
- {{cite web|url=http://chandra.harvard.edu/photo/2003/ngc6888/|title=Crescent Nebula: Live Fast, Blow Hard and Die Young|date=14 October 2003|publisher=Chandra X-Ray Observatory}}
- {{WikiSky}}
- {{cite APOD|title=NGC 6888: The Crescent Nebula|date=11 November 2007|access-date=25 March 2018}}
{{Caldwell catalogue}}
{{Sh2 objects}}
{{NGC70}}
{{Cygnus (constellation)}}
{{Portal bar|Stars|Outer space}}