I’d heard about this effect before, but I hadn’t seen it for real. Well tonight we got a pretty good view of this halo effect around the moon. As the sunlight reflected from the moon passes through the clouds, hexagonal ice crystals refract it into a halo with a 22° radius and even a second one at 44°.
Here’s my attempt at a photograph of the effect. There are some prettier ones at http://www.lumis.com/pictures/Moon_Ring/.