第10页 The Theory of Gravitation

  Kepler's three law are:

  1.Each planet moves around the sun in an ellipse, with the sun at one focus;
  2.The radius vector from the sun to the planet sweeps out equal areas in equal intervals of time;
  3.The squares of the periods of any two planets are proportional to the cubes of the semimajor axes of their respective orbits:T~a3/2