Galileo observed all of the following. Which observation offered direct proof of a planet orbiting the Sun, instead of Earth?

Gravity

Explanation:

Basically, the sun keeps all the planets in the orbital motion by gravitational alignment. Just as the earth and moon have a similar gravitational pull towards each other. Galileo gave the idea of Copernicus theory. The theory also follows the models of the geocentric model of Ptolemy. Stars are at a fixed position from the sun and far away from the sun. As compared to the earth which is nearby and rotates on its axis from right to left.