Johannes Kepler

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Johannes Kepler was born the son of a poor mercenary solider in 1571 in Weil der Stadt, Wurttemburg in the Holy Roman Empire. He began his education in Wurttemburg through a scholarship program designed to produce teachers and Lutheran pastors. In 1589, Kepler entered the theological seminary at the University of Tubingen. It was here that he first learned of Copernican astronomy from Michael Maestlin. The University of Tubingen awarded Kepler his MA in 1591. In 1594 Kepler interrupted his theological studies and accepted an appointment as a mathematics teacher at the Lutheran school in Graz, however, he was later dismissed from the position in 1600 due to religious persecution and a standing order for all Lutherans to leave the district. Earlier that year, Kepler temporarily worked with the Emperor Rudolf II’s Imperial Mathematician, Tycho Brahe. . Kepler later traveled to Prague to join Brahe and work as his assistant until Brahe’s death in 1601, whereby Kepler was appointed successor as The Imperial Mathematician. The appointment was the most prestigious honor in all of Europe for mathematics during his time.

While working as Brahe’s assistant, Kepler was given the task of studying and attempting to understand the orbit for planet Mars. The orbit of Mars was particularly difficult because Copernicus had correctly placed the Sun at the center of the Solar System, but had erred in his assumption of circular planetary orbits. After numerous experiments and mathematical calculations, he finally realized the obits of the planets were in fact not circular as Aristotle had previously insisted and Copernicus assumed correct, but in fact were more elliptical in shape. The fact that Mars has the most elliptical of all orbits that Kepler had data on lead to Kepler eventually formulating the correct theory for the Solar System. After Brahe’s death Kepler was able to obtain all of Brahe’s data and observations. Utilizing the voluminous and precise data of Brahe, Kepler was able to use his realization of the elliptical orbits of the planets to formulate his Three Laws of Planetary Motion, his most important achievement and the one history most notably remembers him for.

Kepler’s first law of planetary motion is “ The orbits of the planets are ellipses, with the Sun at one focus of the ellipse.” The Sun is not at the center of the ellipse but is at one focus. The planet then follows the ellipse in its orbit meaning the planet-Sun distance is constantly changing as the planet goes around its orbit. Kepler’s second law of planetary motion says “ The line joining the planet to the Sun sweeps out equal areas in equal times as the planet travels around the ellipse.” The planet moves faster when it is nearer the Sun, so because of the elliptical motion and the placement of the Sun within that ellipse, the speed of the planet changes as it moves through it’s orbit. The third law of planetary motion is “The ration of squares of revolutionary period for two planets is equal to the ratio of the cubes of their semi major axes.” The third law implies that the period for a planet to orbit the Sun increases rapidly with the radius of its orbit. Mercury, being the innermost planet, takes only 88 days to orbit the Sun, while Pluto, the outermost planet, takes 248 to complete one orbit around the sun.

Kepler’s laws of planetary motion are what he is most remembered for, but he also had a number of other groundbreaking discoveries. He was the first to investigate the formation of pictures with a pinhole camera. He explained the