The Crescent Nebula in Hydrogen Alpha (NGC 6888)

Crescent Nebula in Hydrogen Alpha
All Images Copyright Steve Cannistra

Please click here or on image for a higher resolution view.

Magnitude:  10.0
Size: about 20'
Distance: 4,700 light years
RA: 20h 12m 48s
Dec: 38 degrees 19' 00"

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.

Photographic Details:

Date:  July 3, 2004
Takahashi Sky 90 at f4.5 with field flattener/focal reducer, on the G11 Losmandy Mount.
Autoguider:  SBIG STV with e-finder.
Camera:  SXV-H9
Astronomik Ha filter (13 nm bandpass).
Exposures:  17 x 5' each, binned 1 x 1, 85 minutes total.
Conditions:  Temperature 60 degrees F; below average transparency; very humid; excellent seeing; calm.
No dark, bias, or flat frames used.  Two-star aligned in MaximDL; Sigma combined using RC Sigma Reject MaximDL, followed by DDP in ImagesPlus (IP).  Subsequent levels and curves adjustments in Photoshop CS (16 bit format).  I purposefully avoided overprocessing this area, since I like a more natural look to this region.

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