A 22° halo is a halo, one type of optical phenomenon, forming a circle with a radius of approximately 22° around the Sun, or occasionally the Moon (also called a moon ring or winter halo). It forms as the sun- or moonlight is refracted in millions of randomly oriented hexagonal ice crystals suspended in the atmosphere. The halo is large; the radius is roughly the size of an outstretched hand at arm's length. A 22° halo may be visible on as many as 100 days per year—much more frequently than rainbows.