Crescent Nebula

Crescent Nebula

Emission nebula
Observation data: J2000.0 epoch
Right ascension	20h 12m 7s
Declination	+38° 21.3′
Distance	5,000 ly
Apparent magnitude (V)	+7.4
Apparent dimensions (V)	18′ × 12′
Constellation	Cygnus
Designations	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. It was discovered by Friedrich Wilhelm 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 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". Some observers even can see the Euro symbol shape in a telescope as small as 11 cm with an OIII filter.

See also

• Cygnus Bubble

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