Kids ask: Why does the Earth spin?
"Why does the Earth spin?" asked Brynne Dorsey, 8, a third-grader at Townline School in Vernon Hills.
The Earth was put into a spin when it was formed, according to Geza Gyuk, director of the Adler Planetarium in Chicago.
Most space objects form by collapse. That is to say that objects start far apart from each other in space and then shrink under the influence of gravity. If the original stuff had even a very tiny bit of spin, then as it collapsed the spin would increase.
Gyuk said the idea of spin is like seeing an ice skater who begins to turn in a tight circle and pulls her arms into her sides to create an even faster spin. The spin idea works with a lot of things, even chairs on rollers. There's actually a scientific term for that type of spinning: conservation of angular momentum.
All the planets spin in the same direction. The Earth might have been forced into spinning in an opposite direction, or some other fate could have occurred, when a gigantic object slammed into its surface and knocked a huge hunk off the planet that rocketed into space. That hunk is our Moon.
The Earth's clock was probably reset when the Moon was formed, Gyuk said. Since that cataclysmic event, the Earth's spin has slowly been slowing down. The difference has meant that our Earth takes 24 hours to complete its full rotation. In the time of the dinosaurs, days were only 22 hours long.
Gyuk points to a few more reasons for the slowdown - The moon's tidal forces and the moon's orbital motion around the Earth. As a result, the moon's distance from the Earth has been increasing, Gyuk said.
The Adler Planetarium is celebrating the International Year of Astronomy with a monthly hot topic and a monthly observable object See the planetarium's Web site at adlernet.org for more information.
Check these out
The Cook Memorial Library in Libertyville suggests these titles on the Earth:
• "Earth Cycles," by Michael Elsohn Ross
• "Earth's Journey Through Space," by Trudy E. Bell
• "Why is the Earth Round?" by Patricia J. Murphy
Send in your question
What questions do you have? Send them to Kids Ink, and you might see it right here. Want to know about people, places or things? Or maybe why things happen? The student whose question is answered each week will receive a 1-gigabyte USB flash drive. You can write to kidsink@dailyherald.com. Include your name, age, hometown, grade and school. Teachers can download Kids Ink question forms at our Newspaper in Education Web site nie.dailyherald.com/kidsink.asp.