Q. According to Kepler's third law, the square of the period of revolution of a planet is directly proportional to what?
Answer: The cube of the semi-major axis of its elliptical orbit
Notes: Kepler's third law, also known as the law of harmonics, states that the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its elliptical orbit. This relationship between the time of revolution around the sun and the distance from the sun is a universal property of all objects orbiting the sun, including asteroids and comets besides planets.