Seeking followup observations!
Last new moon, I went to a dark sky site in north-eastern California, near the tiny town of Likely, CA. I had good but not excellent transparency, and I had only moderate seeing. For this reason, I would rate the skies as a Bortle 2. But I could definitely get hints of the Zodiacal Band, especially around the Gegenschein, on all three nights that I spent in the area. I'll write a full OR of all 50-odd objects I observed in a separate post, but in this thread, I want to discuss something I noticed that surprised me, and on which I would appreciate follow up of other deep observers.
Firstly I must admit that I'm still learning to push the limits of what my eyes can see through my scope, and sometimes I toe the line between observation and "noise in my vision system" -- occasionally, I still do make observations that do seem false, so I am happy to stand corrected on the following observation if proven wrong. But the coincidence does seem rather amazing to be an accident.
I'm not sure where I first learned about the M57 outer halo, but apparently, I tried it first at GSSP last year. My notes on Jun 30 2019 say "With a Lumicon UHC on a 10mm Delos, I sensed max thickness on the northern side towards the IC galaxy."
In any case, I decided to give it another shot this time on Oct 15 2020. My logs read:
"Best view in 10mm Delos. Looks very raggedy and spikey. Strongest sensation on WNW side. Really, present all around but strongest WNW. In UHC, glow seems more spikey, but more isotropic."
Now, that's referring to the immediate outer halo that hugs the ring, as seen in this contrast-enhanced POSSII blue plate
Attachment 4057
Then I wrote "Now that [local stray light] is out, in UHC + 10 Delos, I see the outer outer halo! The only reason I believe this very faint feature is real is because it moves with the object! Very weak, could not reproduce clearly second time at the eyepiece." After this point, I didn't try any more and some bothersome local lights emerged. I made the following sketch.
Attachment 4058
I estimated the diameter to be ~50% the FOV of my 10mm Delos, which turns out to be about 10'. After I came back home and tried to look up pictures of the ring nebula in narrow-band, I was very disappointed, because I did not find any large outer halo of 10' diameter. I suspected I'd written down the eyepiece wrong, i.e. 10mm instead of 4.5mm, or simply "seen" something that didn't exist. But after some more searching, to my astonishment, I stumbled upon this OIII image!
http://www.imagingdeepsky.com/Nebulae/M57/M57_OIII.jpg
Here's the full website http://www.imagingdeepsky.com/Nebulae/M57/M57.htm
The website says "960 minutes" exposure with an RCOS 20", and labels the image as "...possible outer halo of M57."
If this observation is true, I would be really surprised. I have a tendency to "complete" faint structures in my head, so whereas I may have only seen a few patches of a donut-like halo, I would extrapolate it to completion. In hindsight, I should have made a more careful observation (project for next time I'm under very dark skies). I still don't know what the "patch" in the image is, since the IC galaxy is roughly at 6:30 clock position in my sketch -- so unless I got my north orientation wrong, that can't be it. It could even just be the tight asterism in that region seen through the filter. It is also reasonable to pick up the outer outer halo even when not seeing the large spikey structures seen in the images at https://www.cloudynights.com/topic/7...i-halo-on-m57/, because we are more sensitive to sharp contrast than slower variations in background brightness.
Now I realize this is not completely out of reason, because with a narrow-band filter, OIII nebulae that appear impossibly faint on the POSS II are still visually feasible -- this is the case with many Abell planetary nebulae in my experience. It also helps that Mel Bartels has been visually discovering IFN (although mine is not one of the fast telescopes he uses). I'm wondering if someone would give it a shot and let me know if they can reproduce this observation, and whether it is within reason.
Here is another pic I found on the internet
https://upload.wikimedia.org/wikiped...7089844%29.jpg
Thank you!
Clear Skies
Akarsh
