Ring Around The Moon

Sometimes, there are very high, thin clouds in our atmosphere. The Cirrus clouds, as they're called, are made of ice crystals. Often, the Cirrus clouds are so thin they are difficult to see. But when the moon's light goes through the ice crystals, the light rays are bent in a way which focuses the light into a circle around the moon. We call it a Halo.

The process is similar to what happens closer to the earth when the sun's light is refracted by raindrops to form a rainbow.

Halos are not at all uncommon. In fact, we've seen them two nights this week here in South Texas. The Cirrus clouds which create the Halo are sometimes seen as the forebearer of a change in the weather. Indeed, the arrival of some storm systems may be preceeded by the arrival of a layer of high clouds and a Halo. I wouldn't go so far as to use a Halo as a forecast tool, though. The Halo's reliability in forecasting change is probably less than 50-50.