halo

A halo is a thin ring of light that sometimes appears around the sun or the moon. Halos are formed by the refraction (bending) of light as it passes through small, hexagonal (six-sided), pencil-shaped ice crystals high in the sky.

The two most common types of halo are the 22 degrees halo and the 46 degrees halo. The number of degrees in a halo refers to the angle by which light is refracted through the ice crystals. For instance, if light is bent at an angle of 22 degrees, it will form a circle of light with a radius (the length of a line segment from the center of a circle to its boundary) of 22 degrees. The 22-degree halo is smaller than the 46-degree halo and more tightly encircles the sun.

A 22-degree halo is formed by ice crystals that are randomly arranged. The light enters one of the six sides and exits through another of the six sides.