What is the meaning of Kepler’s third law?

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How long a planet takes to go around the Sun (its period, P) is related to the planet’s mean distance from the Sun (d). That is, the square of the period, P*P, divided by the cube of the mean distance, d*d*d, is equal to a constant. For every planet, no matter its period or distance, P*P/(d*d*d) is the same number.