Question

Which proportionality does Kepler’s third law describe?

Answer 1

Size of a planet's orbit to sidereal period of the orbit

Answer 2

Answer:

The third law of Kepler describes the proportionality of the orbital period and the  semi-major axis of the orbit.

The square of the period of the orbit of a planet is proportional to the cube of the semi-major axis of the orbit.

The equation of the law is as follows:

$\frac{T^2}{a^3}=constant$

Where $T$ is the period and $a$ is the semi-major axis.