The Moon - Lemmy.World

The Moon just now in the UK. No idea what is creating the halo

That would be a 22° halo, a fairly uncommon atmospheric phenomenon where light refracts through hexagonal ice crystals in the atmosphere resulting in an average deviation from the angle it comes in at by around (funnily enough) 22°.

There are lots of other interesting atmospheric phenomena including sundogs, moonbows, and the much rarer 46° halo!

the much rarer 46° halo

If that's the really huge halo that seems to take up most of the sky, I've only seen that perhaps 3x in my life.

Are they not collectively called coronas, in your part of the world? They are here.

Yeah that’s the one! Only seen it once (coinciding with a supermoon which was frankly surreal).

Coronas are a bit different I believe, though another one of the same group. I’ve always just called them their individual names, with coronas being tighter and more spectrally-distorting than halos. Maybe the only other collective name I’ve heard would be the minimally descriptive “atmospheric phenomenon” but that’s no fun at all.

Not refraction, but diffraction and interference. The droplets (or ice particles or in some cases even pollen) get so small that light stops behaving like rays at those scales.
Corona formation

Ahh yes, that’s the one! Thank you
Thanks, that's interesting! Colloquially they're just called coronas here I think, but it sounds like a misnomer.