Johannes Kepler

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Johannes Kepler (1571 - 1630) was a German mathematician, astronomer and astrologer, he also did a bit of physics. He formulated Kepler's law which explains the orbit of planets.

Kepler's work was pivotal in establishing heliocentrism as the dominating model of the solar system.

Newton was Kepler's beyotch. This may or may not be true.

Kepler is universally acknowledged as having had the most wonderful beard and moustache of all the scientists of his day.

[edit] Kepler's laws

Illustration of Kepler's three laws with two planetary orbits. (1) The orbits are ellipses, with focal points f1 and f2 for the first planet and f1 and f3 for the second planet. The sun is placed in focal point f1. (2) The two shaded sectors A1 and A2 have the same surface area and the time for planet 1 to cover segment A1 is equal to the time to cover segment A2. (3) The total orbit times for planet 1 and planet 2 have a ratio a13 / 2:a23 / 2.

1. Planets orbits describe ellipses, with the sun (or whatever they orbit) being one of the focuses (foci?). Before his work it was thought that they described circular trajectories.
2. The area formed by a planet's trajectory and the sun is directly proportional to the time elapsed. This also means the farther the planet is to the sun, the slower it is.
3. The third law is probably easier to understand in mathematical terms: Where P is the orbital period of the planet (i.e. its year) and a the semimajor axis of orbit (i.e. half its longest "diameter"). In other words: "The squares of the orbital periods of planets are directly proportional to the cubes of the semi-major axis of the orbits."