The Crescent Nebula (NGC 6888)

Crescent Nebula
All Images Copyright Steve Cannistra

Please click here for a medium sized image (55%).
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Magnitude:  10.0
Size: about 20'
Distance: 4,700 light years
Position Angle (Pinpoint):  +11 degrees
RA (J2000): 20h 12m 11s
Dec (J2000): +38 degrees 20' 28"

The Crescent Nebula is not a typical supernova remnant like the Veil.  It is probably a result of the slow release of large amounts of gas from the dying central star seen in the above photograph, known as Wolf-Rayet 136, which has not yet gone supernova.  The stellar winds resulting from the release of this star's outer envelope compress and excite surrounding hydrogen gas, resulting in Ha emission and the characteristic layered texture to NGC 6888.  More information about this interesting region of space can be found here
, and here.  This represents the first light image for the VC200L in f6.1 configuration (based upon plate solve results), yielding a focal length of 1228mm and an image scale of 1.14 "/pixel.  Details may be found in the Equipment section.

Photographic Details:
Date:  July 2, 2008
Scope:  Vixen VC200L at f6.1 (FL = 1228 mm) on the Takahashi NJP Mount.
Autoguider:  SBIG ST-402 with 60mm guidescope, focal length 227mm.
Camera:  Apogee U32 -20C.

Astronomik Ha (6nm).
Exposures:  Ha: 16 x 15' = 240' (unbinned); Total exposure 4 hours.
Conditions:  A clear night sandwiched in between a terrible stretch of weather here in New England.  Seeing only in the range of 3.5".
Post-processing:  Calibrated, debloomed, aligned, and Sigma Clip combined in Maxim.  DDP in ImagesPlus (IP).  Deconvolution (25 iterations) in AIP4WIN.  Further processing in Photoshop CS (16 bit format).  Given the high density of stars in this region, I used one pass of a minimum filter (radius 1) with 50% opacity, masked only to affect the stars, in order to reduce their size and draw attention towards the center of the field.
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