Halo (optical phenomenon)
= Halo
{disambiguate=optical phenomenon}
{wiki}
An atmospheric optical feature produced by interactions with ice crystals. A common $22^\circ$ halo comes from a $60^\circ$ prism path in hexagonal crystals; <minimum deviation> concentrates rays near its inner angular boundary. This differs from the liquid-water path of a <rainbow>.<Optical Effects: Nature's Light Show by the Met Office>[Haloes]{ref}