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Contains:  The star 9Cas
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CTB-1 (Abell 85) Supernova Remnant in HaOIIIRGB

Technical card

Resolution: 2399x1920

Dates:Aug. 13, 2018Aug. 23, 2018Sept. 3, 2018Sept. 12, 2018Sept. 13, 2018

Astrodon Blue Tru-Balance E-Series Gen 2: 10x60" -20C bin 1x1
Astrodon Green Tru-Balance E-Series Gen 2: 10x60" -20C bin 1x1
Astrodon Ha 5nm: 216x240" (gain: 139.00) -20C bin 1x1
Astrodon Ha 5nm: 332x120" (gain: 201.00) -20C bin 1x1
Astrodon OIII 3nm: 733x120" (gain: 201.00) -20C bin 1x1
Astrodon Red Tru-Balance E-Series Gen 2: 10x60" -20C bin 1x1

Integration: 50.4 hours

Darks: ~50

Flats: ~50

Bias: ~250

Avg. Moon age: 8.82 days

Avg. Moon phase: 34.35%

Bortle Dark-Sky Scale: 6.17 job: 2251068

RA center: 359.885 degrees

DEC center: 62.473 degrees

Pixel scale: 2.695 arcsec/pixel

Orientation: 210.487 degrees

Field radius: 1.150 degrees

Locations: Backyard Red Zone Observatory, Taylor, MI, Michigan, United States

Data source: Backyard


This was brutal finishing this off. Usually this time of year there are a lot of clear nights. I started in anticipation of that; not so much so. My goal with this project was to bring out more OIII than what I have seen before and bring out more detail in Ha in general making the background more subtle. I combined this in a Ha and OIII bicolor palette and then added in RGB stars.

CTB1 is a nearby supernova remnant (SNR) with an apparent diameter of about a half a degree (about the same size as a Full Moon). Upon early discovery, CTB1 was thought to be a planetary nebula, so Abell included it in his catalog of planetary nebulae as Abell 85. It was identified as a SNR by van den Bergh et al. in 1972 based upon its optical half-circular shape consisting of radiative filaments. Deeper images taken in H-alpha by Fesen (1993) show that it has a complete circular shape except for the unusual breakout structure toward the northeast, which also shows up in X-Ray images. Distance and age estimates are 10,000 light years, and 7,500 – 11,000 years, respectively. It spans nearly 100 light years.



Douglas J Struble

Sky plot

Sky plot


CTB-1 (Abell 85) Supernova Remnant in HaOIIIRGB, 


            Douglas J Struble