Kepler's Law of Periods states that the time it takes a planet to orbit the sun is directly proportional to the planet's average distance from the sun. In other words, the farther a planet is from the sun, the longer it takes to complete one orbit.
Johannes Kepler, the German mathematician and astronomer, first stated this law in 1609. He discovered that the square of the period of a planet's orbit (the time it takes to complete one orbit) is directly proportional to the cube of the planet's average distance from the sun (its semi-major axis). This relationship is expressed mathematically as:
T^2 = k R^3
where T is the period of the planet's orbit, R is its average distance from the sun, and k is a constant of proportionality. This law of periods is one of three laws of planetary motion formulated by Kepler and is a fundamental part of our understanding of the solar system.