A Halo Around the Moon

Explanation: Have you ever seen a halo around the Moon? This fairly common sight 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 Moon Halo . A similar Sun Halo may be visible during the day. The town in the foreground of the above picture is San Sebastian , Spain . The distant planet Jupiter appears by chance on the halo 's upper right. Exactly how ice-crystals form in clouds remains under investigation .