Crescent Nebula

Crescent Nebula
Observation data: J2000.0 epoch
Type	Emission
Right ascension	20h 12m 7s[1]
Declination	+38° 21.3′[1]
Distance	5,000 ly
Apparent magnitude (V)	+7.4
Apparent dimensions (V)	18′ × 12′
Constellation	Cygnus
Physical characteristics
Radius	-
Absolute magnitude (V)	-
Notable features	-
Other designations	NGC 6888,[1] Sharpless 105, Caldwell 27
See also: Diffuse nebula, Lists of nebulae
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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. It was discovered by Friedrich Wilhelm Herschel in 1792.^[2] 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^[3] to 400,000^{[citation needed]} 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 a telescope as small as 8cm (with filter) can see its nebulosity. Larger telescopes (20cm 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

• APOD (2007-11-11) – NASA Astro Picture of the Day: Image by Franck Bugnet
• NOAO image
• Chandra image
• Image by Arran Hill
• Image by Daniel Lopez
• Sharpless Catalog 105
• Crescent Nebula on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images