Stranger ring around the moon

[Mutley]

In addition to the moon halo, just saw another moon ring. This one was fainter than the moon halo, centered more or less on the zenith, with the moon lying on the circumference. I was able to trace almost a complete circle around the zenith, fading out as it got close to the moon. Picture below, which I've enhanced a bit. I've never seen anything like this before. Any ideas?

[Mutley]

Well, it's a real thing - "Lunar circumzenithal arc" , half way down this Wikipedia page:

https://en.m.wikipedia.org/wiki/Circumzenithal_arc

[Leo S]

It looks more like a parhelic circle to me. Circumzenethal arcs are only found directly above the light source.

[Mutley]

Interesting, thanks @Leo S. Does you're note imply that you only get circumzenithal arcs in equatorial zones, where the sun gets closer to the zenith (in the case of sun-generated zenithal arcs) ?

[Leo S]

3 hours ago, Mutley said:

Interesting, thanks @Leo S. Does you're note imply that you only get circumzenithal arcs in equatorial zones, where the sun gets closer to the zenith (in the case of sun-generated zenithal arcs) ?

You're very welcome. Circumzenithal arcs (CZA's) are not uncommon at UK latitudes. My wife and I used to hunt for them in the day time, and would see them multiple times in a week usually. Tip: keep an eye out for wispy cirrus clouds, and when you spot them, keep checking every minute or two as they can come and go very quickly.

That's not the case for the closely related circumhorizon arcs, (CHA's) which occur directly below the light source/Sun. If the Sun's altitude is not high enough, they can't be seen, and here in the UK the Sun's altitude is usually not high enough, so they are very rare here in the UK. Moving further south/toward the equator where the Sun's altitude is higher increases the odds of seeing a CHA.

[Leo S]

I thought it had gone, but found what is probably the best reference web site for ice halos that I've come across. Looks like it's been archived!