Crescent Nebula Explained

Crescent Nebula
Type:Emission
Epoch:J2000.0
Ra:[1]
Dist Ly:5,000
Appmag V:+7.4
Size V:18′ × 12′
Constellation:Cygnus
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.[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 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

External links

Notes and References

  1. NGC 6888 . 2007-04-23.
  2. Web site: NGC 6888 . The NGC/IC Project . Erdmann . Robert . dead . https://web.archive.org/web/20120520010558/http://www.ngcicproject.org/ngcicdb.asp . 2012-05-20 .
  3. Web site: WR 136 . 25 March 2018 . jumk.de.