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| Emission nebula | |
|---|---|
 The Crescent Nebula, as taken by an amateur astronomer | |
| Observation data: J2000.0 epoch | |
| Right ascension | 20 12 7 |
| 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 |
| See also: Lists of nebulae | |
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".
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NGC 6888 in Hydrogen and Oxygen Light. HOO Palette. Imaged by Don Christopher Deaver
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Crescent Nebula in H-alpha and OIII. Imaged with a 715mm focal length telescope. The hydrogen gas is red. The oxygen is blue.
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Image of NGC 6888 using H-alpha filter.
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Picture of NGC 6888 captured in narrowband by amateur astronomer Luca Moretti
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NGC 6888 imaged in 3 nm hydrogen-alpha and oxygen-III narrowband at 2800mm focal length by amateur astronomer Patrick Hsieh.
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See also
References
- ^ "NGC 6888". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2007-04-23.
- Erdmann, Robert. "NGC 6888". The NGC/IC Project. Archived from the original on 2012-05-20.
- "WR 136". jumk.de. Retrieved 25 March 2018.
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.
| Caldwell catalogue | |
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| List |
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| See also | |
| New General Catalogue 6500 to 6999 | |
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