The Crescent Nebula, also known as NGC 6888 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 250,000 - 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 faint object located about 2 degrees SW of Sadr. To image the outer (blue-ish) shell, a OIII filter was used to allow the ultra-narrow, 3nm, Oxygen-III line to pass through only.
8x60sec were taken for each color, Red, Green, Blue and used for the star colors only.
30x120sec were used for the H-Alpha line and
40x120sec were used for the O-III line.
Exposure times: RGB 8x1min each, O3 40x2min, Ha 30x2min,total: 3hrs, 14min
Kit: TS-Optics PHOTOLINE 152 mm f/8 Triplet APO, Astrodon 3nm filters, QHY268M, 10Micron GM1000