Best Answer

T^2 is proportional to r^3 (or a^3).

More exactly, T^2 = (2*pi)^2/(GM)*r^3 (or a^3).


  • T is the period
  • r is the radius of the orbit
  • a is the length of the semimajor axis of the orbit
  • pi is about 3.142
  • G is the gravitational constant 6.67x10^-11
  • M is the mass of the planet
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Q: According to Kepler's third law the square of the planets period in years is?
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Related questions

What do the length of the planets year and its distance from the sun have in common?

There is a relationship between the planets distance from the sun and the time taken for one orbit (planets year), described in Keplers third law. The square root of the time taken to orbit the sun is proportional to the cube of the average distance between the sun.

What was keplers theory?

He was the first person to suggest that the planets don't move in circles and the planets don't always move at the same speed all the time. He and Isaac Newton made more accurate predictions than the other scientists e.g. Artistotle, Ptolemy, Copernicus, Tycho Brahe.

Why do planets differ in their orbital speed?

Because according to Kepler's laws the orbital speed of a planet is proportional to the square root of the reciprocal of the distance: v = d-½.

What were Keplers laws of?

Kepler's Laws of Planetary Motion:1] Each planet moves in an elliptical orbit with the sun at one focus2] The line form the sun to any planet sweeps out equal areas of space in equal time intervals3] The squares of the times of revolution (days, months or years) of the planets are proportional to the cubes of their average distances from the sun.

How did newtons work on orbits add to work Kepler had done?

Newton derived Keplars findings from Newton's Theory of Gravity. Thus, newton 'explained' the basis for Keplars findings and extended them.

Is the square of the orbital period of a planet proportional to the cube of the average distance of the planet from the Sun?

Yes, according to Kepler's third law of Planetary Motion.