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Kepler's three laws of planetary motion, simplified, are: 1) The orbit of a planet is an ellipse. 2) A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. 3) The square of the time it takes for a planet to orbit the sun is proportional to the cube of the distance to the sun. Simply, all three of these laws can be combined to explain precicely how planets orbit the sun.