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Why moon hits your eye like a big pizza pie

This just in for tonight's eclipse: Scientists now know why the moon

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It's a Y2K lunar celebration: Last month, the full moon moved in close to shine as bright as it can get. Tonight, it will treat us to a total eclipse.

All of North and South America will have grandstand seats as the moon slips into, through, and out of the darkest part of Earth's shadow over a 3-hour, 24-minute period beginning at 10:01 p.m. EST. Its light will start to dim about an hour earlier.

To add perspective to the show, a father-son research team has nailed down the reason we think the moon is larger than it really is when it's on the horizon. As it turns out, it has nothing to do with the atmosphere. Nor is it an optical illusion that makes us think the moon is closer. Actually, it's an optical illusion that makes us think the moon is farther away.

That notion - that the moon appears bigger because we think it's farther away - is so counterintuitive that scientists discounted it for centuries. But physicist Lloyd Kaufman at IBM's Almaden Research Center in San Jose, Calif., and his psychologist father, James Kaufman, at Long Island University in Brookville, N.Y., say they have proof that ancient astronomers got it right when they posited just such a theory long ago.

According to data released earlier this month, the illusion occurs because of the way the brain and eyes perceive distant objects. The brain takes clues from the intervening landscape to judge how far away an object is. The eyes, however, judge distance by the size of objects, measuring how big an angle they take up in our field of vision.

Our visual system combines this information to adjust our perception so objects keep their right proportions. This is why we don't mistake a distant truck for a toy.


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