The Crescent Nebula, NGC 6888,
is an interesting nebula with a pecular and unique shape. At
the center of the Nebula is a Wolf-Rayet star (WR 136) that
shines at magnitude 7.4, a star in the latter part of its life-cycle
that is shedding off its mass in the form of a strong, stellar wind.
It has shed off all its hydrogen gases leaving its helium
core exposed, a dynamic that will result eventually in a supernova
explosion. The stellar winds stirred up the surrounding interstellar
dust and gas causing ripples across the visible part of the nebula,
which is now seen because the ultraviolet radiation of WR136 exciting
the gases of the nebula, causing it to fluoresce.
nebulae have similar Wolf-Rayet Stars at their center. In
the case of NGC 6888, it is classified as an emission nebula
because it emits its own light, although it shares many characteristics
of planetary nebulae itself. The Crescent is quite difficult
to observe visually because of its rather even surface illumination.
To see it, you'll need medium to large aperture and dark skies.
Observatory near Azle, Texas
Date: June 26 & 27, 2005
Temperature: 72 degrees
RCOS RC and Paramount ME
Camera: SBIG STL-6303e (Ha)
and SBIG STL-11000M (RGB) astro
Filter: Custom Scientific 4.5nm Hydrogen-alpha
Exposure Info: HaRGB
image - 120:80:50:80 minutes (20 minute subexposures for Ha; 10
minute subs for RGB; all unbinned)
Registration, DDP, and RGB combine in MaxIm DL 4. HaRGB
combine, Levels/curves, sharpening, and
noise removal in Photoshop CS.
Notes: H-alpha data blended
50% with the red channel to improve color saturation. H-alpha
data was then used again as luminance.
on the image for higher resolution (1600 x 968 pixels)
Here is a wide-field shot of the area extending south-east from the Crescent
Nebula, NGC 6888, shown in the lower-left of this image. The total exposure is
over 3 hours in Hydrogen-alpha light, a method that allows for capturing detail
of the hydrogen gases being emitted in this area. It
is a region of interesting
nebulosity from the Cygnus Milky Way, a southern extention of IC1318 around
Gamma Cygni; however, none of the nebulosity in this image has a designation, at
least none that I'm aware of. There are star clusters contained within the dust.
Open clusters NGC 6871 and NGC 6883 are included at the right side of the image.
NGC 6874 is at the upper left.
Location: The Ballauer Observatory near Azle, Texas
2004 and September 8, 2004
Scope/mount: Takahashi FSQ-106 @ f/5 and Tak NJP mount
Filter: Custom Scientific 4.5 nm Hydrogen
Exposure Info: Grayscale, Hydrogen-alpha
filtered image - 205 minutes (15
min. subexposures unbinned).
Processing Info: Dark frame calibration, flat-fields,
registration, and average combine in MaxIm 4.0.
Digital-Development in MaxIm. Levels, Curves, selective unsharp
mask, and selective gaussian blur in Photoshop CS.
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