"Lunar halo" appears over Deep South

Published: Jan. 22, 2013 at 9:41 AM CST|Updated: Jan. 22, 2013 at 9:45 AM CST
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By: Jay Grymes - email

BATON ROUGE, LA (WAFB) - Many people saw a ring around the moon Monday night and were curious about exactly what caused it.

It is a "lunar halo" and is produced by a deck of high, thin cirrus clouds.

Because they are so high up in the atmosphere, cirrus clouds are composed of ice crystals rather than water droplets. The ice crystals are acting like tiny reflectors/mirrors, reflecting the moonlight at a precise angle. Because the angle is "precise," we get a circle with the moon located in the very center.

Lunar haloes are somewhat rare because they require a combination of events:

The moon must be located overhead, or nearly so

There can be few, if any, clouds in the low and middle levels of the atmosphere

A thin deck of cirrus clouds, so thin that you can see the stars through them

By the way, did you see the "star" sitting right next to the moon? That's the planet Jupiter, making Monday night's halo even extra special.

"Solar haloes" also occur occasionally, but are generally less common (harder to see) than the lunar halo, because of the advantage of the night sky with the moon.

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