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Weekend


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July 31, 2009

Strange But True!

Q. Lovely moonlit night has you and your sweetheart out in the backyard enjoying the sight. Suddenly she takes several steps away from you and bends over, peering out horizontally through her legs. No, she's not “mooning” you, so what is she up to?

A. She says she's out to defeat the ancient, well-known “moon illusion,” the most striking illusion in the natural landscape. This is the apparent enlargement of the moon when it's near the horizon, appearing about 50 percent bigger than when it's overhead, explains Jearl Walker in “The Flying Circus of Physics.” Actually, the moon always occupies about half a degree in our view, so the illusion is psychological. Its primary cause seems to be that we associate a low moon with the terrain in front of us, and based on contrast with the terrain, the moon LOOKS bigger.


 
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