Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2010 February 8
See Explanation. Go online for the highest resolution available.

A Sun Halo Over Cambodia
Credit & Copyright: Nagy Attila

Explanation: Have you ever seen a halo around the Sun? 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 Sun halo. A similar Moon halo may be visible during the night. Pictured above, a nearly complete sun halo was photographed high above the ancient Bayon temple in Angkor, Cambodia. Exactly how ice-crystals form in clouds remains under investigation.

View this page (with external links) online at
http://apod.gsfc.nasa.gov/apod/ap100208.html.


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