Question

What is the third law of Kepler's Planetary Motion

Answer 1

Kepler's laws of planetary motion are three scientific laws describing the motion of planets around the Sun. The orbit of a planet is an ellipse with the Sun at one of the two foci.
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Answer 2

This is a mathematical law, and your students need calculators with square roots, also 3/2 powers and 2/3 powers (and maybe cube roots or 1/3 powers, same thing)..

    If two planets (or two Earth satellites--works the same) have orbital periods T1 and T2 days or years, and mean distances from the Sun (or semi-major axes) A1 and A2 then the formula expressing the 3rd law is

(T1 / T2)2   =   (A1 / A2)3

    Students will ask right away--we can count days to get orbital period T (although it may be tricky, we need subtract the Earth's motion around the Sun)--but how do we know distance A?

    In truth, we don't, but notice only ratios of distances are needed, and units don't affect ratios. For instance, suppose "Planet 2" is the Earth, and all times are in years. Then T2 =1 (year) and we can measure all distances in Astronomical Units (AU) , the mean Sun-Earth distance, so that A2 =1 (AU). The law then becomes, for any other planet,

(T1)2   =   (A1)3......

Hope it was helpful for u....