Kepler's laws | |
—pl n | |
three laws of planetary motion published by Johannes Kepler between 1609 and 1619. The first states that the orbit of a planet describes an ellipse with the sun at one focus. The second states that, during one orbit, the straight line joining the sun and a planet sweeps out equal areas in equal times. The third states that the squares of the periods of any two planets are proportional to the cubes of their orbital major axes |