Astrophysics

The recessional velocity of a galaxy is directly proportional to its proper distance from the observer: $v = H_0 D$.

The orbit of a planet is an ellipse with the Sun at one of the two foci.

A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.

The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit: $T^2 \propto a^3$.