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The Question

(Submitted November 07, 1996)

How does the Sun just stay in one spot and how do all of the other planets stay on course/track ?

The Answer

The planets in our solar system stay on track because of the force of gravity. This is identical the same force that holds us on the Earth. Imagine shooting a rocket--the faster you fire the rocket, the farther it goes. If you fire it fast enough, it will escape the Earth's gravity and go into outer space. You could also fire the rocket into an orbit around the Earth by propelling it fast enough that it doesn't hit the ground, but not fast enough to escape the Earth's gravity. This is what NASA does when it launches the space shuttle into an orbit. In the same way, all of the planets, along with other things like comets, are in an orbit around the Sun. Just like the Sun's gravity keeps the planets into a stable orbit, the planets exert an equal force on the Sun (gravity is a two-way street), but the Sun is so massive that it hardly budges.

Andy Ptak and the Ask an Astrophysicist team

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