NGC 6888 – Crescent Nebula
Pictures taken on Tuesday 24th May 2016 from Grassobbio (BG)
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 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 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”.
Takahashi FSQ 106 EDXIII F/3.6
CCD Moravian G2 8300
H-Alpha 7Nm Filter
Guide scope Tecnosky 60/228mm
Guide camera Starlight Xpress Lodestar X2
Mount Sky-Watcher AZ-EQ6
H-Alpha 6 x 1200s
RGB 6 x 600s (thanks to Efrem Frigeni)