Crescent Nebula

11. Crescent Nebula


NGC 6888  RA: 20h 12.0'  Dec: +38 21'   Cygnus (Cyg)

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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 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.

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".
 

Image Information

Location Miller Lake ON
Date Aug 10 2013
Optics AstroTech AT8IN
Filters Baader MPCC
Mount Celestron CGE
Camera Canon/Hutech 500DH
ISO 800
Subexposures 15
Exposure Length 300
Guider NH2/ST-4
 

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All images copyright © 2006-2021, Rick Saunders
Main text descriptions sourced from Wikipaedia.
Sky position information is based on IP geolocation and is therefore approximate.