Harmonic Law Activity 
Go back to lesson.
  Kepler’s third law (the Harmonic Law), relates the orbital period of a planet (that is, the time it takes a planet to complete one orbit) to its mean distance from the Sun.  This law states that the closest planets travel at the greatest speeds and have the shortest orbital periods.  Using the NASA planetary data pages, have students find the orbital period and the mean orbital radius for each planet.  Enter the data into a spreadsheet or manually create a line graph, with each planet's mean orbital radius on the X-axis and its orbital period on the Y-axis.  
 
Planet Orbital Radius (X) Orbital Period (Y)
     
     
     
     
     
     
     
     
     
  Ask students to describe any general trends they see:  
  • Is there a systematic relationship between period and radius for the planets?
  • How would you describe this relationship in words?
  • Is the relationship you observe consistent with Kepler's third law?
  • How could you improve your test for consistency?