Planetary motion

Copernicus
Kepler

The Copernican theory versus the geocentric theory

The Copernican theory states that, in the solar system, the Sun is at the center and the planets move around it. This theory replaced the existing one, which believed that the Earth was at the center and that the other planets and the Sun moved around it..

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Kepler's Laws

Kepler's first law says that the orbit of the planets of the solar system is an ellipse with the Sun at one of its foci. Kepler's second law says that a line joining the sun with any one of the planets sweeps an equal area per unit time. Kepler's third law says that the square of the orbital period of any planet is proportional to the cube of the semi-major axis of its orbit.