Cometary Globule 12: A Dark Nebula That's Not All Dark

OTA: PW17 f /6.8
Camera: FLI ML16803
Observatory: Deep Sky West
Date of Capture: Apr, '22
Date of Processing: Dec, '23

Exposures:
R: 20 x 600 sec
G: 16 x 600
B: 16 x 600
L:  31x 600
Total Exposure time: 13.8 hours
Image Width: 43.3 arc-minutes

Processing Tools:
1.    Commercial: PixInsight, Topaz (Studio2, Photo AI2), Photo Director 365
2.    Pixinsight Addons: NoiseXTerminator, BlurXTerminator, StarXTerminator, Normalize Scale Gradient
3.    My Scripts: NB_Assistant, AC_Restar, Subframe Weighting Tool (Excel w/ J. Hunt)

Target Description:
This region hosts a significant dark nebula (Cometary Globule 12 or CG 12) and the reflection nebulae NGC 5367. Reflection nebulae result when the light from one or more bright stars illuminates a gas cloud. Unlike an emission nebula, the brightness emanates dominantly from a "filtering" of the star's light and not from ionized gas atoms (but some degree of ionization is not precluded). Our blue sky arises from the same physics as the two reflection nebulae in this image: blue light has a short wavelength and is more subject to Rayleigh scattering. Rayleigh scattering occurs when the light bounces off gas particles that are small with respect to wavelengths of light. However, other factors also contribute to why our sky, and these reflection nebulae, are blue. C. S. Baird lists the spectrum of the incident light, the attenuation of other colors (absorption by the gas), and even our visual system's interpretation of colors as factors that contribute to the blue color of our sky and these nebulae. (Also, thanks, Wikipedia!)

As for the stars illuminating NGC 5367 are young stars that appear to be part of an unusually low-density area for star formation to initiate. Williams, et al. (1977) suggest that these stars may have been spawned due to a supernova explosion into an irregular, clumpy molecular cloud.

Processing Description:
Dark nebula seem driven to conceal their structure, and sometimes, it is not so much concealing structure lacking structure. Regardless, NGC 5367 neither lacks nor conceals its structure. The trick is making the nebula bright enough to reveal slight differences in brightness by enhancing contrasts on multiple scales. In my opinion, that is not an area where PixInsight excels but where Topaz Studio and PhotoDirector, working together, can get the job done. I don't think you will find many versions of this nebula on Astrobin that have been fashioned in this manner. However, almost all of them portray NGC 5367 as significantly brighter than the background, although it is still primarily gray or cream in tint. An overall grayish flush arises from a subequal mix of primary colors but not necessarily a precisely equal mix. Bringing out those subtle color variations was my objective here. Hope you like this result.

BTW, the only masking done on this object involved reinstating the stars and the galaxy at the left into the processed starless image.

Statistics:
Distance: 2,100
Pixel Span at Target: 6B km

Alex Woronow