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Contains:  NGC 6357
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NGC6357 - The Scorpion in Scorpius (SHO), 


            Andrew Klinger
NGC6357 - The Scorpion in Scorpius (SHO)
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NGC6357 - The Scorpion in Scorpius (SHO)

Technical card

Dates:May 31, 2019

Ha 5nm: 35x300" (gain: 200.00) -10C bin 1x1
Astrodon OIII 3nm: 33x300" (gain: 200.00) -10C bin 1x1
Astrodon SII 3nm: 34x300" (gain: 200.00) -10C bin 1x1

Integration: 8.5 hours

Darks: ~64

Flats: ~30

Bias: ~200

Avg. Moon age: 26.57 days

Avg. Moon phase: 9.60%

Bortle Dark-Sky Scale: 3.00

Basic astrometry details job: 2783068

RA center: 17h 26' 33"

DEC center: -34° 11' 38"

Pixel scale: 2.022 arcsec/pixel

Orientation: 1.278 degrees

Field radius: 1.560 degrees

Resolution: 4482x3282

Locations: Atoka dark site, Atoka, Oklahoma, United States

Data source: Traveller


There are a lot of names for this intricate nebula, however none of them really seem to fit the bill. "The Lobster Nebula" as well as the "War and Peace Nebula" are used often but I personally see a scorpion with raised claws and a faint curved tail. Not to mention this nebula resides in the constellation Scorpius, a fitting home. So hear me out astronomical community and lets make this happen!

In this false-color narrowband image, I display the Sulphur and Hydrogen emissions as the warm red-orange colors and the Oxygen emissions as the teal-blue range. I typically save narrowband imaging for home, but since this target never rose above 22° I used my dark site's unobstructed view to capture this nebula. In the core of this nebula lie some of the most massive stars known, and the surrounding nebulosity shows off a chaotic display of gas and dark dust.

OTA: William Optics GT81 w/0.8x reducer (382mm fl at f/4.7)
74mm aperture stop-down ring (brings scope to f/5.2)
Mount: Orion Sirius EQ-G (HEQ-5)
Guidescope: Orion 50mm guidescope
Guiding camera: Orion StarShoot Autoguider
Imaging camera: ZWO ASI1600MM-Cool

QHYCCD PoleMaster


Location: Atoka, OK (Bortle 3)
Dates: 5/31/19, 6/26/19, 6/27/19
Gain: 200 Offset: 50
Camera temp: -10C
Sii: 34x300" Astrodon 3nm
Ha: 35x300" Astrodon 5nm
Oiii: 33x300" Astrodon 3nm
Total integration time: 8hr 30min
64x darks per calibration (master from library)
30x flats per calibration
200x bias per calibration (master from library)

Batch PreProcessing script to generate calibrated images
DynamicCrop each master
DBE each master

Luminance Processing:
Duplicated the master Ha to use as the luminance
TGV noise reduction (via Jon Rista's method)
ArcsinhStretch and HistogramTransformation to bring to non-linear
HDRMultiscaleTransform to reveal core
MultiscaleLinearTransform for sharpening
CurvesTransformation for slight contrast

Preparing separate Sii, Ha, and Oiii linear masters for tonemapping (applied to each master individually):
TGV & MMT noise reduction (via Jon Rista's method)
ArcsinhStretch and HistogramTransformation to bring to non-linear
Removed stars via StarNet++
Further removed background artifacts with MMT

Combined prepared Sii, Ha, and Oiii masters with ChannelCombination:
R: Sii
G: Ha
B: Oiii

Tonemap Processing:
Invert>SCNR Green>Invert to remove magenta
DBE to help with uneven color casts
Several a/b channel CurvesTransformations using ColorMasks to alter the colors to an aesthetically pleasing palette
CurvesTransformation for saturation
CurvesTransformation for slight contrast

Combined Tonemap with Luminance using LRGBCombination
CurvesTransformation to balance background color
MorphologicalTransformation for slight star reduction
UnsharpMask with a StarMask to harden up the soft stars a tad



Andrew Klinger
License: None (All rights reserved)

Sky plot

Sky plot


NGC6357 - The Scorpion in Scorpius (SHO), 


            Andrew Klinger

In these public groups

Narrowband imaging