Image Credit & Copyright: Anthony Ayiomamitis (TWAN)
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 setting of the above
picture is Athens San
Sebastian, Greece. The
distant planet Jupiter appears by chance on the halo's left.
Exactly how ice-crystals form
in clouds remains under investigation.
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