A 22° halo is an optical phenomenon that belongs to the family of ice crystal halos, in the form of a ring with a radius of approximately 22° around the Sun or Moon. When visible around the moon, it is called a moon ring or winter halo. It forms as the sun- or moonlight is refracted in millions of hexagonal ice crystals suspended in the atmosphere.[1] The halo is large; the radius is roughly the size of an outstretched hand at arm's length.[2] A 22° halo may be visible on as many as 100 days per year—much more frequently than rainbows.
source:Wikipedia
