Since my processing technique gets better and weather doesn't give any support, I have reprocessed some older images. There is now star colors added and other processing is tweaked too.
NGC 6888 as a wide field image
Ra 20h 12m 7s Dec +38° 21′ 3"
Image is in HST-palette, (HST=Hubble Space Telescope)
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)
Natural color composition from the emission of ionized elements, R=80%Hydrogen+20%Sulfur, G=100%Oxygen and B=85%Oxygen+15%Hydrogen to compensate otherwise missing H-beta emission. This composition is very close to a visual spectrum.
Image is shot with a QHY8 and the Tokina AT 300mm f2.8 lens at full aperture.
Original versions from November 2008, with technical details:
A closeup image of the Crescent Nebula
This image is shot with a much longer focal length, about 2000mm, with a Meade LX200 GPS 12", Baader narrowband filters and a QHY9 astronomical camera. Image is in HST-palette.
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