1.29 Kepler's laws

Kepler's First law states that planets move in ellipses around the Sun, with the Sun off center at the focus of the ellipse. Kepler's second law describes the fact that a planet moves fastest in its orbit when it is nearest the Sun. If you imagine a line connecting the planet and the Sun, the line sweeps out equal areas in equal times. Kepler's third law relates the size of a planet' s orbit to the time period it takes the planet to complete one orbit around the Sun. The law states that the period in years squared equals the semi-major axis of its orbit in Astronomical Units cubed.