Obscured Spiral Galaxy in Cepheus
Instrument: 12.5" f/5 Home made Newtonian
Platform: Astrophysics 1200 QMD
CCD Camera: SBIG 10XME NABG with Enhanced Water Cooling
Guider: SBIG ST4
Exposure: Ha^RGB = 120:40:40:40
RGB Combine Ratio: 1: 1.05: 1.11
Filters: AstroDon RGB Tricolor
Location: Payson, Arizona
Elevation: 5150 ft.
Sky: Seeing FWHM = 5.5 arcsec (Maxim DL - 10min subframe), Transparency 7/10
Outside Temperature: 60 F
CCD Temperature: -20 C
Processing Tools: Maxim DL, Gralaks Sigma, Photoshop, PixInsight, Starizona Debloomer.
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Often portrayed in browns
and yellows, this very highly obscured face on spiral requires
special attention during processing to get the colors close
to reality. In this part of the sky in Cepheus, the dust in the
Milkyway not only obscures deep space galaxies and stars, but
imparts a very strong yellow color cast as well. To remove the
color cast and reveal the galaxy in its natural hues, a technique
known to many professional day time photographers to remove color
casts was used - Histogram Equalization. To do this, we use a
mask to select only the galaxy and adjust the histograms to start
and end in the same location for each of the three colors. Most
notably, the blue histogram is strongly truncated on the top
end, and must be brought back into sync with the others. A brown
nearly monochrome galaxy is transformed almost by magic to a
standard blue armed spiral, with a golden core and now visible
for the first time - hordes of pink HII regions in the arms.
NGC6946 is only
inclined 1 degree, and thus presents its face to us clearly.
Listed at 9.6 magnitude, its large size of 12 arcminutes spreads
out its light into a very faint disk, with little central condensation.
The galaxy is listed as a SAB spiral and has as you would expect
a very ruddy color index of .80, which is almost as red as a
K type star. The faint galaxy to the lower right of the the main
spiral is MAC 2033+6005, a 17th magnitude object with a size
listed as .4 arcminutes. The field is devoid of any other faint
galaxies because of the extreme dust in this region of the sky.
2 hours of hydrogen alpha data was taken, and combined into the
R channel at 100% with lighten, and the blue channel at 10% using
lighten as well to maintain the proper pink coloration of Hydrogen.
Extreme care was used to not white clip or oversaturate the hydrogen
hues. The stars and galaxy remain close to G2V using this technique.