When cirrus-type clouds are in the sky, we can see a ring around the sun or moon. This ring of light is called a halo. The light forms from ice crystals in the clouds, which can refract or reflect light. Most halos form at 22-degree radius. A radius is a line from the ring to the center of the sun (or moon.) Halos can form at a 46-degree radius. Rarely, halos can form multiple rings with various radius numbers. The largest possible ring has a 90-degree radius that can be seen around the sun, called Hevel’s halo.