Crescent Nebula

Template:Short descriptionTemplate:More citations neededTemplate:Infobox nebula 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.<ref name=ngcic>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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<ref name="jumk">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> to 400,000Template: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.

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".Template:Cn

Gallery

• NGC 6888 HOO By Don Christopher Deaver.jpg

  NGC 6888 in Hydrogen and Oxygen Light. HOO Palette. Imaged by Don Christopher Deaver

• 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.

• Crescent Nebula in H-alpha.jpg

  Image of NGC 6888 using H-alpha filter.

• NGC 6888 (Crescent Nebula) bicolor.jpg

  Picture of NGC 6888 captured in narrowband by amateur astronomer Luca Moretti

• 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.

• 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.

• CrescentBicolorHunterWilson.jpg

  The Crescent Nebula, as taken by an amateur astronomer

See also

• Cygnus Bubble

External links

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