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 sunlight 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 arms length.  As light passes through the 60° apex angle of the hexagonal ice prisms it is deflected twice resulting in deviation angles ranging from 22° to 50°.  The angle of minimum deviation is almost 22° (or more specifically 21.84° on average; 21.54° for red light and 22.37° for blue light).  This wavelength-dependent variation in refraction causes the inner edge of the circle to be reddish while the outer edge is bluish.  As no light is refracted at angles smaller than 22° the sky is darker inside the halo.  A 22° halo may be visible on as many as 100 days per year—much more frequently than rainbows.