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.

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 8cm (with filter) can see its nebulosity. Larger telescopes (20cm or more) reveal the crescent or a Euro sign shape which makes some to call it the “Euro sign nebula”.

Imaging telescopes or lenses: Takahashi TSA-102
Imaging cameras: Atik 383L+ mono
Mounts: SkyWatcher NEQ6 pro II
Guiding telescopes or lenses: EZG60
Guiding cameras: QHYCCD QHY5 Mono
Focal reducers: Takahashi TOA-35
Software: Pleiades Astrophoto, S.L. PixInsinght 1.8 RC7
Filters: Baader Planetarium OIII, Baader Planetarium Ha 7nm 2″
Dates: Aug. 15, 2014, Aug. 16, 2014
Locations: Pantano
Frames: 
Baader Planetarium Ha 7nm 2″: 69×600″ -20C bin 1×1
Baader Planetarium OIII: 66×600″ -20C bin 1×1
Integration: 22.5 hours
Darks: ~20
Flats: ~16
Bias: ~20

Author: Jose Luis Ricote
AstroPhotography of the day by SPONLI 31 Aug 2014