NGC 6946: seen through the Galactic plane (Wei-Hao Wang)

NGC 6946: seen through the Galactic plane

NGC 6946 is a face-on spiral galaxy. It has a Galactic latitude of 11.7 deg, very close to the Galactic plane. This means that its light has to go through the dense interstellar medium of the Milky Way before reaching us. In this picture, reflected light from interstellar dust can be seen everywhere around NGC 6946. The light of NGC 6946 is also strongly attenuated and reddened by the interstellar dust absorption, making it appear redder than it should be.

For this picture, I tried two different color balance. The first one is a standard G2V balance, using Sun light as the white reference. This is Rev.B. Here, everything has the "right" color that our eye would have seen, but as mentioned above, this color of NGC 6946 is actually redder than its original color. To recover NGC 6946's true color, I corrected the interstellar dust absorption. Toward the direction of NGC 6946, the Galactic foreground absorption is 0.938 mag at V band. This translates to 1.242 mag at B band and 0.702 mag at R band. This allows me to correct the absorption and restore NGC 6946's original color. This is Rev.C. Now the spiral galaxy has the blue color that it should have. Unfortunately, as a consequence, the foreground stars and dust who do not suffer from such absorption (or have much weaker absorption) become too blue.

(The processings for Rev.B and Rev.C are almost identical, to give a fair comparison of their colors. Also, Rev.B and Rev.C are simple RGB composition, without L and H-alpha, while the final version is an LHaRGB composition.)

The final version has a color balance between Rev.B and Rev.C, as it looks more natural to me.

Rev.D is an enhanced version, to better show the outer spirals of NGC 6946 and the foreground dust clouds.

Final
Original
B
C
D

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Status	Advanced success
Started	...
Astrometry.net job	6646710
PixInsight job	FUFTZ4IS2KY0W7JTHHF91AUDHWSS4VPL
PixInsight queue size	n/a
PixInsight stage	TASK_LOG

RA (center)	20h34m54s.896
RA (top/left)	20h37m21s.960
RA (top/right)	20h32m27s.453
RA (bottom/right)	20h32m31s.229
RA (bottom/left)	20h37m19s.559

Dec (center)	+60°08′45″.23
Dec (top/left)	+60°26′50″.39
Dec (top/right)	+60°26′42″.65
Dec (bottom/right)	+59°50′29″.90
Dec (bottom/left)	+59°50′37″.54

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