Very faint greenish arc covering most of the frame

It takes a bit of doing to see this, but if you go to the browser and scan the image up and down you can detect that there is a broad diffuse greenish arc (running from 1 o’clock to about 8 o’clock) in this frame. Is this an artefact? I cannot see any bright stars that might have caused flare in the optics that could cause this.

PS: I have since enhanced the image and you can clearly see that this is a bubble of gas - now identified as planetary nebula EGB6.

Just checked the WISE dust map - there is no corresponding structure there, but this greenish arc does seem to correspond with the edge of a large blob of intensity in the H-Alpha map.

From the number of stars, I’d guess that this field has a low galactic latitude. If so, then the greenish color and the “large blob of intensity in the H-alpha map” point to an HII region. I think there are catalogs of such, but am not 100% sure. Do you know how to search for such a catalog?

I have no idea! This is the “blob” in H-Alpha (at lower zoom) which corresponds with the arc - see also the faint star that seems to be at the centre, in another post.

This is the field with contrast and brightness enhanced using Photoshop. The bubble that this arc is a part of is now clearly seen. This green ring matches closely the extent of the red blob in the H-Alpha map.

Screenshot 2019-01-06 at 21.35.41.jpg

Yes it is planetary nebula EGB 6 as can be found in SIMBAD. With the bright blue thing in the middle being a white dwarf or something similar.

Nice find, here is a better image of the PN;

Nice photo. It’s a pity the DECaLS and SDSS images don’t have that sensitivity - we could see so much more!