ATMOSPHERIC HALOS AND THE SEARCH FOR ANGLE X

The familiar ring around the moon is an example of an atmospheric halo, which is a signature of ice crystals in the air, though the focus here is on odd radius halos. The shape of the ice crystals responsible is only just becoming understood, and is determined by angle x, which has yet to be identified. Tape and Moilanen (their affiliations are not stated), discuss the phenomenon and its possible causes. Some of the material is accessible to lay readers with some scientific background, and some requires college-level mathematics. One of their goals is to encourage the former to notice atmospheric halos--for example different sized ones around the sun--and to marvel at the mystery they present as well as their beauty.