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Circular Arc in the California Nebula

NGC1499 NGC Objects Deep Sky Nebula Artifacts
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Bob Stevenson avatar
Bob Stevenson avatar
Hello,
I just finished a shot of NGC1499 and noticed something odd. In the upper left of my image is the outline of part of a circle. Does anyone know what this might be? It is one of those things that you cannot 'unsee' once you notice it.

My shot:
https://www.astrobin.com/full/77hwe6/0/

Other shots:
https://www.astrobin.com/365228/?nc=user
https://www.astrobin.com/full/275412/0/

Has anyone researched this?
Thanks!
Well Written Respectful Engaging
Bob Lockwood avatar
Bob Lockwood avatar
I and some of my imager friends have seen this and thought the same thing, even centered on it and did long expousurs of it to see if it maybe some kind of shock wave, or a PN. Nothing came up and never showed more then what you are seeing. It shows up really well in NB images, and it is easy to see in my image I did of it in NB.

https://www.astrobin.com/d30zk4/?nc=user
Bob Stevenson avatar
Bob Stevenson avatar
Your shot is amazing Bob. Good to know others have noticed it as well and looked into it. I too was hoping I would find reference to a shock wave or something similar, but found nothing!
Dave Erickson avatar
Dave Erickson avatar
Yes there is a dark nebula up there it is not circular in a wider FOV…
Regards,
Dave
Nadir Astro avatar
Nadir Astro avatar
Now that you told me. I can't unsee it on my own image.

https://www.astrobin.com/full/3bikfb/0/