Why is there a rainbow around the sun or moon?

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Story Published: Oct 4, 2006 at 1:08 PM PST

Story Updated: Dec 21, 2009 at 9:05 AM PST

By Scott Sistek

You’ve all seen rainbows on those days where it's raining and the sun's out at the same time. But what about those times when you see a rainbow-like halo around the sun or moon?

It's the same physics, really. The halos (or, sometimes known as "sundogs" around the sun) are usually seen when there are high clouds overhead. Those clouds are made of tiny ice crystals, which will refract the sunlight much like a prism will. And voila! You have a rainbow halo around the sun. It works the same way with moonlight. It's usually a sign that rain is on the way, as high clouds usually precede a storm front.

Sometimes the rainbow isn't in the form of a halo, but just colors a streak of clouds -- the ice crystals in that cloud were at just the correct angle from the sun to produce the prism effect shown here. The one on the left was taken May 24, 2002, while the one on the right was taken July 19, 2003 in Tacoma, and the bottom one was taken June 3, 2006 from Spokane. 

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