First up, welcome, and it is a very good image.
We confirm that there is nothing at that spot in for example the
APOD image.
We agree that it doesn't look anything like a dust bunny as it is light rather than dark. If you had done flats, using a different filter, which did have a dust spot, and now took the shot with a cleaner filter, you can end up with a lighter ring such as you have, but it doesn't look like that.
Don't think it's a true transient astrophysical object such as comet or a Klingon, but you never know. We've seen other people accidentally photograph a distant comet.
Our first guess was that it is a "residual" image of a bright star from a focusing run, but arguing against that you've got a CMOS camera and we think it's only CCD's that show residual or ghosting images. A characteristic of residual images is that they'd be fainter in each progressive sub.
Another guess is that it is a reflection of a bright star off the back of a filter or the chip cover.
One way of getting around reflection images is to move the scope by an amount large compared with the diameter of the artifact between subs. The idea is that the reflection moves in the opposite direction to the field. You then use statistics to find what's common across all the subs. The easiest is a median combine. More sophisticated and powerful is a Winsorized combine, which is what we use.
Have another go, next new moon, but frame it differently, and see if the blob is gone, or if it moves relative to the image.
Once again, a really good image, apart from the Space Invader that you've captured. Astonishing what folk such as you are achieving with these cooled CMOS cameras.
Best,
Mike and Trish
