According to Kepler's third law of planetary motion, the square of the time period of a planet is proportional to which power of its semi-major axis?

Solution

1. Kepler's third law relates the orbital period $T$ and the semi-major axis $a$.
2. The mathematical expression is $T^2\propto a^3$.
3. Therefore, the square of the time period is proportional to the third power of the semi-major axis.
4. Hence the answer is (C).