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 .
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