Johannes Kepler

Johannes Kepler was a German mathematician, astronomer and astrologer and generally a key figure in the 17^th century scientific revolution. He is best known and is for famous for his eponymous laws of planetary motion which was codified by later astronombers basked on his works Astronomia nova, Harmonices Mundi and Epitome of Copernican Astronomy. All these works also provided one of the foundations for Isaac Newton’s theory of universal gravitation. He lived from December 27^th 1571- November 15^th 1630.
In the era Kepler lived in, there was no clear distinction between astronomy and astrology but there was a very strong division between astronomy and physics. He had also been known to incorporate religious arguments and reasoning into his work. He was motivated by the religious conviction that God had created the world according to an intelligible plan that is accessible through the natural light of reason. This new astronomy he had made was named “celestial physics.”

Kepler contributed a mathematical law of motion to astronomy which were three laws. These three laws were as followed:
1. The orbit of every planet is an ellipse with the sun at one of the foci. An ellipse is characterized by its two focal points; see illustration. Thus, Kepler rejected the ancient Aristotelean and Ptolemaic and Copernican belief in circular motion.

2. A line joining a planet and the sun sweeps out equal areas during equal intervals of time as the planet travels along its orbit. This means that the planet travels faster while close to the sun and slows down when it is farther from the sun. With his law, Kepler destroyed the Aristotelean astronomical theory that planets have uniform velocity.

3. The squares of the orbital periods of planets are directly proportional to the cubes of the semi-major axes (the "half-length" of the ellipse) of their orbits. This means not only that larger orbits have longer periods, but also that the speed of a planet in a larger orbit is lower than in a smaller orbit.

These three laws are crucially important to astronomy and mathematics law of motion.