The correct answer is - the heliocentric system.
By using the telescope, Galileo Galilei managed to observe the movements of the Sun, Moon, the planets in the Solar System, and he was mapping their movements on the sky, and also he was comparing their movements to the Earth's position. With this, he managed to notice that insted of the popular belief that the Sun, Moon, and the other planets are moving around the Earth, that it is actually the opposite of it, and that the Sun was the center of our Solar System, and that all the planets and moons were orbiting around it, while the only object that hold its position as it was initially thought was the Moon, because it orbits around our planet. So Galileo contributed to the theory of the heliocentric system.
