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Look Up: Tonight, 'Supermoon' Is Closer To Earth

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Head outside at sunset tonight and look up at the sky. If the full moon seems a tad larger than normal to you, that means one of two things: You are exceptionally perceptive, or you were already expecting to be dazzled, after hearing some of the buzz about this year's "supermoon."

It turns out that all full moons are not created equal. That's because the moon's orbit around the Earth isn't a perfect circle — it's an ellipse. And tonight, we're in luck.

"We will have moon closest to the Earth at the exact moment, or within a minute or two of when it becomes full," says Andrew Fraknoi at Foothill College in Los Altos, Calif., and senior educator at the Astronomical Society of the Pacific. "And this has no cosmic danger or significance but it means the moon will be a little bit brighter and a little bit bigger in our sky."

Fraknoi says this supermoon is a good excuse to take a romantic stroll. And for the best Hollywood effect, head out around sunset, when the moon is close to the horizon.

"When you look at the moon on the horizon, especially when there are buildings in the distance, it looks huge," he says. "And because this supermoon will be a tiny bit bigger, it will be an especially interesting moon illusion this Saturday night."

The moon illusion is simply a trick of the eye, but a convincing one.

Beachgoers know that high tides are higher and low tides are lower around full moons. The supermoon does add a bit of an extra tug, since it's a little bit closer to Earth than usual.

"But the difference of it being a little bit closer in its orbit or a little bit farther is only a question of about an inch in the height of the water," Fraknoi says.

So if you were expecting a supermoon to rock your world, sorry. You'll have better luck waiting for a giant asteroid to smash into our planet.

But there is a darker side to this story. Fraknoi says it used to be that events like supermoons and planetary conjunctions were 100 percent happy news, "but now more and more, I think partly because of tabloid television, when something is happening in the sky, it leads people to be afraid. Astronomer David Morrison has coined this new phrase called 'cosmophobia.' "

Since sunlight falls on all the moon's surface at some point, astronomers will tell you that the moon does not actually have a dark side — despite what we learned from Pink Floyd. But the human mind apparently does.

Copyright 2012 National Public Radio. To see more, visit http://www.npr.org/.

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