Three days ago marked 436 years since the birth of Johannes Kepler. Born in Germany on December 27, 1571, Kepler was the first human being who was able to put together all the observations from others and himself, and truly see and understand, and define laws of planetary motion. For this he had to make the leap from religious faith into the pure essence of mathematics, astronomy, and science, something that on those days could get you killed. Kepler law’s were the ones that led Newton to his own discoveries and laws on motion and gravitation.
Kepler’s three laws of planetary motion:
- Kepler’s First Law: The Law of Ellipses: 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.
- Kepler’s Second Law: The Equal-Areas Law: 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.
- Kepler’s Third Law: The Harmonic Law: 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.
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[References and sources: NASA and Wikipedia]