Kepler's Third Law of Planetary Motion states that the square of the orbital period of a planet is directly proportional to the cube of the average distance between the planet and the Sun. This can be mathematically expressed as:

T² ∝ r³

Where:

* T is the orbital period (time it takes for the planet to complete one orbit)

* r is the average distance between the planet and the Sun (semi-major axis of the elliptical orbit)

This law is a fundamental principle in understanding the motion of planets in our solar system and beyond.