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A graph showing Kepler's 3rd law.
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Kepler's 3rd Law: P2 = a3

Kepler's 3rd law is a mathematical formula. It means that if you know how long it takes a planet to go around the Sun (P), then you can determine that planet's distance from the Sun (a).

This formula also tells us that planets far away from the Sun take longer to go around the Sun than those that are close to the Sun.

Check out the table of orbital data for the planets. You will notice that Venus' orbital period (P) is longer than Mercury's, and the Earth's period is longer than Venus', and Mars' period is longer than Earth's...

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The Fall 2009 issue of The Earth Scientist, which includes articles on student research into building design for earthquakes and a classroom lab on the composition of the Earth’s ancient atmosphere, is available in our online store.

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