NGC6888 – The Crescent Nebula


The Crescent Nebula, in the constellation Cygnus, is the result of the bright central star entering the second phase of burning out. The hypothesis is that in its first phase, the red giant star used up all its hydrogen fuel and expelled its outer shell of gas. About 250,000 years ago, the star evolved into a Wolf-Rayet type and began ejecting its outer shell in a strong stellar wind. The wind collided with the hydrogen cloud from the first phase, compacting it into complex shells. Strong ultraviolet radiation ionizes the hydrogen gas, causing it to glow red. The star, WR136, will likely explode as a supernova within the next million years.

Celestron 9¼" at f/7.5 on a Celestron CGE equatorial mount
SBIG ST-8XM camera
SBIG CFW-10 filter wheel with Astrodon TruBalance LRGB filters
Optec TCF-S focuser
Optec Pyxis camera rotator
Guide scope: Celestron 100mm f/5 refractor and ST-402 camera.
Imaging and autoguiding with MaxIm DL 4.11
H-a   10.3 hours (124 x 5 min.) unbinned @ -10°C and -15°C
Processing Dark and flat processing in CCDStack
Images combined with SD Mask CCDStack
Levels and curves, highpass filter in Photoshop CS
Date and Location 8, 16, 26, & 29 July 2006   
Montpelier, VA    N 37° 49' 12", W 77° 42' 06"