22° halo

It forms as sunlight or moonlight is refracted by millions of hexagonal ice crystals suspended in the atmosphere.

Hexagonal, randomly oriented columns are usually put forward as the most likely candidate, but this explanation presents problems, such as the fact that the aerodynamic properties of such crystals leads them to be oriented horizontally rather than randomly.

Alternative explanations include the involvement of clusters of bullet-shaped ice columns.

The ice crystals in the clouds all deviate the light similarly, but only the ones from the specific ring at 22 degrees contribute to the effect for an observer at a set distance.

As no light is refracted at angles smaller than 22°, the sky is darker inside the halo.

[6] Another way to intuitively understand the formation of the 22° halo is to consider the following logic: Angle of rotation =

Another phenomenon resulting in a ring around the Sun or Moon—and therefore sometimes confused with the 22° halo—is the corona.

Unlike the 22° halo, however, it is produced by water droplets instead of ice crystals and is much smaller and more colorful.

[3] In folklore, moon rings are said to warn of approaching storms.

[7] Like other ice halos, 22° halos appear when the sky is covered by thin cirrus or cirrostratus clouds that often come a few days before a large storm front.