All datasets acquired with Moana from DSO (Dark Sky remote Observatory), near Fort Davis, TX, USA.
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 starWR 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[
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.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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