Question

1. what is the main principle of keplers third law?

keplers third law focuses on the area a planet covers during its orbit.
keplers third law focuses on the mass of the planets and their orbital period around the sun.
keplers third law focuses on the shape the planets follow in their orbit.
keplers third law focuses on the relationship between the distance a planet is from the sun and the orbital period

Explanation:

Kepler's third law, also known as the law of harmonies, states that the square of the orbital period ($T$) of a planet is proportional to the cube of the semi - major axis ($a$) of its orbit around the Sun, mathematically expressed as $T^{2}\propto a^{3}$. The first option refers to Kepler's second law (equal - area law). The second option is incorrect as mass of planets is not a factor in the basic form of Kepler's third law (in the form $T^{2}\propto a^{3}$, it is derived under the assumption that the mass of the Sun is much larger than the mass of the planet). The third option refers to Kepler's first law (planets move in elliptical orbits). The fourth option correctly describes the relationship in Kepler's third law.

Answer:

Kepler's third law focuses on the relationship between the distance a planet is from the sun and the orbital period.