Large preview image HERE: http://3.bp.blogspot.com/-QvljZDh_hcM/Uj3IJDr03oI/AAAAAAAAKEo/YdfuuKVjXPY/s0/NGC6888_Wide.jpg
Image is in Mapped colors from the emission of ionized elements, R=Sulfur, G=Hydrogen and B=Oxygen.
Star colors are mixed from the NB channels, Red=H-a, G=O-III and B= 85%O-III + 15%H-a.
The Crescent Nebula, also known as NGC 6888, Caldwell 27 and Sharpless 105, is an emission nebula in constellation Cygnus, about 5000 light years distance.
It is formed by the fast stellar wind from the Wolf-Rayet star, WR 136 (HD 192163), colliding to an slower moving wind ejected by the same star when it became a red giant, around 400.000 years ago.
The result of the collision is a glowing shock shell around the star. Apparen size of the shell is 18' x 12' and the real size is about 25 x 16 light years.
This image covers about three degrees horizontally. (Area of six full Moons side by side)