CTB1, a very faint supernova remnant in Cassiopeia

My latest addition is this picture of an object which has not been photographed that often, probably because it has a very low surface brightness. CTB1 is a nearby supernova remnant in the constellation of Cassiopeia with an apparent diameter of about half a degree. Upon early discovery, CTB1 was thought to be a planetary nebula, so Abell included it in his catalog of planetary nebulae as Abell 85. Further research showed that CTB1 is in fact a supernova remnant. Distance and age estimates are 10,000 light years, and 7,500 – 11,000 years, respectively. It spans nearly 100 light years.
As the object is very faint, it requires a lot of exposure time. Main portion was spent on Ha and O3, with a smaller amount of RGB for the stars.

CTB1 (Abell 85)

Telescope: 16″ f3.75 Dream Scope
Camera: FLI ML16803
Mount: ASA DDM85
Exposure: 35.5 hours (156x300s Ha + 161x300s O3 + 3x30x300s RGB)
Date: August 2017 (data acquisition) – August 2020 (post processing)
Location: Southern Alps, France


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