Halo Sun

Atmospheric halo around the sun as seen from Sweden. Large halo around the Moon or the sun occurs when high thin clouds containing millions of tiny ice crystals cover much of the sky. Each ice crystal acts like a miniature lens. Because most of the crystals have a similar elongated hexagonal shape, light entering one crystal face and exiting through the opposing face refracts 22 degrees, which corresponds to the radius of the Sun or the Moon Halo.