Celestial hemisphere:  Northern  ·  Constellation: Gemini (Gem)
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Abell 21 - Medusa Nebula - SHO + RGB Stars - 60 Hours - ASI1600MM Pro - ONTC 8" Newtonian - CEM60 - Voyager Advanced, 



    
        

            Rowland Archer
Abell 21 - Medusa Nebula - SHO + RGB Stars - 60 Hours - ASI1600MM Pro - ONTC 8" Newtonian - CEM60 - Voyager Advanced
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Abell 21 - Medusa Nebula - SHO + RGB Stars - 60 Hours - ASI1600MM Pro - ONTC 8" Newtonian - CEM60 - Voyager Advanced

Getting plate-solving status, please wait...
Abell 21 - Medusa Nebula - SHO + RGB Stars - 60 Hours - ASI1600MM Pro - ONTC 8" Newtonian - CEM60 - Voyager Advanced, 



    
        

            Rowland Archer
Abell 21 - Medusa Nebula - SHO + RGB Stars - 60 Hours - ASI1600MM Pro - ONTC 8" Newtonian - CEM60 - Voyager Advanced
Powered byPixInsight

Abell 21 - Medusa Nebula - SHO + RGB Stars - 60 Hours - ASI1600MM Pro - ONTC 8" Newtonian - CEM60 - Voyager Advanced

Acquisition details

Dates:
Oct. 31, 2022
Frames:
Astrodon Gen2 I-Series Tru-Balance Blue 1.25": 1076×60(17h 56′) (gain: 139.00) -15°C bin 1×1
Astrodon Gen2 I-Series Tru-Balance Green 1.25": 120×60(2h) (gain: 139.00) -15°C bin 1×1
Astrodon Gen2 I-Series Tru-Balance Red 1.25": 138×60(2h 18′) (gain: 139.00) -15°C bin 1×1
Astrodon H-alpha 3nm 1.25": 693×120(23h 6′) (gain: 200.00) -15°C bin 1×1
Astrodon OIII 3nm 1.25": 303×120(10h 6′) (gain: 200.00) -15°C bin 1×1
Astrodon SII 5nm 1.25": 210×120(7h) (gain: 200.00) -15°C bin 1×1
Integration:
62h 26′
Avg. Moon age:
6.55 days
Avg. Moon phase:
41.15%
Bortle Dark-Sky Scale:
4.00
Mean SQM:
21.00

Basic astrometry details

Astrometry.net job: 6526226

RA center: 07h28m58s.6

DEC center: +13°1608

Pixel scale: 1.462 arcsec/pixel

Orientation: 273.336 degrees

Field radius: 0.341 degrees

Resolution: 1393x937

File size: 1.7 MB

Locations: Caswell Canyon, Anderson, North Carolina, United States

Data source: Backyard

Description

The Abell 21 planetary nebula is also known as Sharpless 2-274 and the "Medusa Nebula."  
According to Wikipedia, it was thought to be a supernova remnant until its reclassification
in 1971 as a planetary nebula by Soviet astronomers.  It's about 1500 light years distant and 
4 light years across.  Located in Gemini, it's a nice winter target although it is rather faint so
benefits from longer integration times.

This data was acquired over many nights between January 2021 and March 2022.
Up until late January 2022, the data was acquired using my homebrew scheduler add-on to Voyager. 
My scheduler didn't have a way to balance data acquisition between filters and so the amount 
of data per filter varies by quite a bit.  Once I switched to Voyager Advanced in February 2022,
further data was balanced by channel.  This doesn't affect strength in the final image, it only 
means, e.g., the Ha data had less noise than SII.  That said, there was enough data in each channel
that the resulting image was pretty clean.

I calibrated the data with SiriL and GESS - GESS is an automation add-on for SiriL that lets me
calibrate a night's worth of data from three scopes with one click.  I don't think I could keep up 
with the data from the three all-night hard working scopes otherwise :-).

Calibrated data was integrated with PixInsight's evolving and excellent WBPP batch processing
program.  Further processing in PixInsight followed these steps:

DynamicCrop
DynamicBackgroundExtraction on each monochrome image
S, H and O combination using PixelMath - S and H in the R channel, O and H in the G channel, O in the B channel,
much playing with factors controlling the contribution of each filter until happy with the result
R, G and B star combination using ChannelCombination
Star Removal of the narrow band images with Russell Croman's fantastic Star XTerminator - 
the starless NB images were processed that way until near the end 
Star Removal of the RGB image with Star XTerminator - creating a stars -only image for recombination later
Russell Croman's Noise XTerminator with a range mask applied to protect the nebula - another excellent tool
Stretch with HistogramTransformation
Curves to increase contrast and brightness of the masked nebulosity
SCNR to kill the green
More Curves to increase color saturation
HDRMultiscaleTransform to bring out detail
A light application of Noise XTerminator once again 
LocalHistogramEqualization for more detail
RGB stars added back with PixelMath using the formula recommended by Star XTerminator

Over to Photoshop
Bodoni's Astrophotography Tools to increase star color
Russell Croman's StarShrink for a slight reduction in star size
Save as PNG
Upload to Astrobin :-)

Comments

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Abell 21 - Medusa Nebula - SHO + RGB Stars - 60 Hours - ASI1600MM Pro - ONTC 8" Newtonian - CEM60 - Voyager Advanced, 



    
        

            Rowland Archer