Hemisphere:  Northern  ·  Constellation: Cassiopeia (Cas)  ·  Contains:  9 Cas  ·  PGC2796252  ·  PK116+00.1  ·  The star 9Cas
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CTB 1 / Abell 85, 


            Gary Imm
CTB 1 / Abell 85, 


            Gary Imm

CTB 1 / Abell 85

Imaging telescopes or lenses: Takahashi TOA-130NFB

Imaging cameras: ZWO ASI6200MM Pro

Mounts: Astro-Physics Mach1GTO

Guiding cameras: ZWO ASI174MM

Software: Pixinsight  ·  Main Sequence Software Sequence Generator Pro  ·  Stark Labs PHD2 2.6.3

Filters: Chroma OIII 3nm  ·  Chroma Red 2" unmounted  ·  Chroma Ha 3nm  ·  Chroma Blue 2" unmounted  ·  Chroma Green 2" unmounted

Accessory: ZWO M68 OAG  ·  ZWO EFW 2″X7  ·  Takahashi Flattener TOA-67  ·  Feathertouch Focuser Boss II Electronic Focusing Control

Dates:Aug. 29, 2020Sept. 18, 2020Sept. 19, 2020

Chroma Blue 2" unmounted: 30x120" (gain: 0.00) -5C bin 1x1
Chroma Green 2" unmounted: 30x120" (gain: 0.00) -5C bin 1x1
Chroma Ha 3nm: 36x300" (gain: 100.00) -5C bin 1x1
Chroma OIII 3nm: 36x300" (gain: 100.00) -5C bin 1x1
Chroma Red 2" unmounted: 30x120" (gain: 0.00) -5C bin 1x1

Integration: 9.0 hours

Avg. Moon age: 4.93 days

Avg. Moon phase: 31.39%

Astrometry.net job: 3871959

RA center: 23h 59' 17"

DEC center: +62° 26' 16"

Pixel scale: 1.580 arcsec/pixel

Orientation: -2.135 degrees

Field radius: 1.030 degrees

Resolution: 4000x2452

Locations: Backyard (Mag 20.8 - Bortle 4.5), Onalaska, Texas, United States

Data source: Backyard


This object is a very faint supernova remnant located 10,000 light years away in the constellation of Cassiopeia at a declination of +62 degrees. The CTB stands for "CalTech B list radio source", which is where it was first identified. It has an apparent diameter of about a half a degree, the same size as our full moon.

When discovered, it was thought to be a planetary nebula, so Abell included it in his catalog of planetary nebulae as Abell 85. The dominant light is from energized Hydrogen (Ha) and Oxygen (OIII) atoms, which show up in my HOO image as red and cyan, respecitively. The surrounding Ha nebulosity in the image has been shown to be related to CTB1 as well.

All of the sources agree that this object is a Supernova Remnant (SNR). But I am struck at the degree of similarity between this object and Sh2-308, which is not a SNR but a Wolf-Rayet star in the pre-supernova phase. Both are spherical with many filaments and a breakout region. In fact, the famous van den Bergh, in a 1973 paper, said "It is rather remarkable that the optical shell of CTB1 is morphologically almost indistinguishable from the filamentary shell that surrounds the sixth-magnitude WN5 star HD50896", the latter being the source star for Sh2-308.

More amazingly, both objects appear to be undergoing deformation characteristic of bi-polar jets. In this object, the breakout section is polar opposite of a section in the lower right at about 5 o'clock which appears to be seeing the onset of a breakout as well. So this object seems more like a Wolf-Rayet nebula than a SNR to me, although I am not doubting the research that says it is a SNR.



  • Final
    CTB 1 / Abell 85, 


            Gary Imm
  • CTB 1 / Abell 85, 


            Gary Imm


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CTB 1 / Abell 85, 


            Gary Imm