Physlet Illustration: Kepler's Third Law

 

 

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a = AU 
A planet orbits a star under the influence of gravity. The distance grid is in Astronomical Units (AU), and the time is shown in years.  The animation begins from the point of aphelion, and the semi major axis of the planet's elliptical orbit may be adjusted (4 AU < a < 20 AU). Can you verify Kepler's Third Law?

Hints:

  1. Determine the period of the planet's orbit for several values of  a.
  2. How does the period change as you change a?
  3. Can you verify Kepler's Third Law? (In these units, the Kepler's Third Law constant is 1 yr/AU3/2.)

Reference

See Walker, Section 12-3

Illustration written by Steve Mellema