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The Earth will start to spin more slowly, but won't stop
By Hope Babowice | Daily Herald Columnist

Ever since an object struck the Earth billions of years ago, the speed at which it spins has been slowing. It will keep slowing but it will never stop spinning completely, experts say.


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Published: 5/27/2009 12:00 AM

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The Grayslake Area Public Library suggests these science titles:

• "Gravity," by Chris Woodford

• "Earth," by Elaine Landau

• "Earth," by Robin Birch

• "Planets, Stars, and Galaxies: A Visual Encyclopedia of our Universe," by David A. Aguilar

• "First Space Encyclopedia," by Caroline Bingham

"What will happen if the world stops turning?" asked Mikayla Poehler, 10, a fifth-grader at O'Plaine School in Gurnee.

The Earth started spinning around 4.5 billion years ago when it was formed, according to Dr. Geza Gyuk, director of astronomy at the Adler Planetarium. Since then the Earth has kept turning, taking almost 24 hours to make one full turn.

The speed of the rotation, about 1,000 miles per hour at the equator, used to be much faster. A Mars-sized object struck the Earth billions of years ago, knocking a hunk off our planet that became the Moon.

Gyuk said: "Since then the spin of the Earth has been slowly slowing down as the tides from the Moon transfer the spin to the orbit of the Moon. In the far future, the Earth will spin much more slowly, but it will never stop." At the same time, the Moon is moving farther away from the Earth.

What if you wanted to slow the spin?

"First of all," Gyuk said, "You'd have to do it very gently." The speed at which the Earth rotates now causes a bulge at the equator. If the Earth moved more slowly, the shape of the Earth would change.

"The resulting shifting of the Earth's surface as the stresses are redistributed would cause tremendous earthquakes all across the globe."

Temperature and time of day would be affected. "Whatever part happened to be facing the Sun would start to heat up." The sunny side would remain sunny 24 hours a day, and the dark side would be dark all day long - for six months at a time. The sunny side would be hot and strong winds would develop.

"The part that was away from the Sun would cool down," Gyuk said. The dark side of the Earth would experience temperatures like the freezing cold in Antarctica or even colder.

Since the Earth would continue its orbit around the Sun, every six months the 24-hour day side would become a 24-hour night side.

"All in all, not a very pleasant scenario," Gyuk said.

For more information about astronomy exhibits and camps at the Adler Planetarium, see