① The law of ellipse: the orbit of all planets around the sun is an ellipse, and the sun is at a focus of the ellipse.
②The law of area: the area of the line between the planet and the sun is the same in the same time interval.
③ Law of Harmony: The square of the sidereal time () of all planets around the sun is proportional to the cube of their orbit semimajor axis (ai), ie.
Since then, scholars have modified the first law to read: The orbits of all planets (and comets) are conic sections, and the sun is at one of their focal points. The second law is only accurate if the mass of the planet is much smaller than the mass of the sun. If one considers that planets also attract the sun, this is a two-body problem. The precise formula of the revised third law is: (where m1 and m2 are the masses of the two planets; ma is the mass of the sun).