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I'm not getting what Kepler's Third Law is about

  1. Nov 5, 2015 #1
    How R^3/T^2 is a constant, or is it just the simple relationship between the distance between a planet to a star in a solar system and the period for that planet to orbit the star?
  2. jcsd
  3. Nov 5, 2015 #2


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    It's a constant for the whole solar system. For example, suppose ## R_e ## is the semimajor axis of Earth's orbit, ## T_e ## is the period (i.e., 1 year in this case), ## R_m## is the semimajor axis of Mars's orbit, and ## T_m ## is the period for Mars (1 Martian year). Then we have ##T_e^2/R_e^3 = T_m^2/R_m^3 ##.
  4. Nov 5, 2015 #3


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    I found wikipedia's explanation quite satisfying. The relation holds for all forces that quadratically decline with distance and small masses compared to the central sun's mass.
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