NGC6888 / Crescent Nebula  Classification: Emission nebula, NGC 6888, Caldwell 27, Sh2-105 Constellation: Cygnus (CYG) Object Location: Ra 20h 12m 40s Dec +38° 24’24° (current) Size & Distance: 18 x 12, Apx 5000 light years Date & Location: 09-27-2014 Palomar Mountain, CA. Exposure: HaOlllOlll, Ha= R, 4 @ 15m, HaOlll=G, Olll=B, 6 @ 15m, all (bin 1x1) Optics: Telescope Engineering Company APO180FL @ f/5.23 using an Astro-Physics TCC160 F/L 941mm Mount: Astro-Physics 1200 GTO / ATS 10x36 Pier Camera: FLI-ML6303E @-20c / CFW2-7 / FLI-Atlas focuser / Guided by SBIG ST-I, w /OAG. FOV 67.5x101.4 Filters: Astrodon 3nm Ha, Olll Software: MaxImDL 6.06, Photoshop CS5, Topaz Lab Notes: Sky conditions: Average seeing, calm winds, Temp 65° Image Field of view is 68 x 101 arc-min. Look close, bottom right, you can see Soap Bubble 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. It was discovered by Friedrich Wilhelm 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.