This is the 2nd target I have used the Optolong L-Ultimate 2" filter and I like the results, I was considering purchasing the Optolong L-Extreme 2", but I think I will wait. I have 3 filters the L-Ultimat, L-Pro and L-Enhance, so far I am happy with the results.
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.It is a rather small object located about 2 degrees SW 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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