Keplerian Orbits

Definition

Johannes Kepler is famous for his three laws of orbital motion for the planets in the solar system. The first two were presented in his Astronomia nova. In essence, they state that planets move in elliptical orbits, sweeping out equal areas in equal times. The powerful third law surfaces in his Harmonice Mundi, where Kepler shows that the square of the planet’s orbital period is proportional to the cube of the orbit’s semimajor axis. Newton reformulated the problem in terms of masses and showed how the masses of the orbiting bodies enter into the third law. When objects follow Newton’s formulation and move in orbits that follow Kepler’s laws, they are said to have Keplerian orbits.