From Glossary of Meteorology


A halo in the form of a bright white spot as far below the horizon as the sun is above it.

The subsun is explained by reflection by the horizontal faces of oriented ice crystals (e.g., large hexagonal plates). Such crystals are never perfectly horizontal with the result that the shape of the subsun changes slightly with solar elevation, being circular for high suns and increasingly teardrop-shaped for low suns.