Johannes Kepler was the German astronomer who developed the laws of planetary motion. Kepler initially planned to become a minister in the church, but after taking a teaching post in 1594 he became interested in mathematics and astronomy. While he was working at Graz, he published his first paper (1596) which showed that five regular (platonic) solids could fit alternately inside each other, and that these could be used to estimate the distances from the Sun of the six planets that were known at that time. Kepler moved to Prague in 1600 and concentrated on the study of Mars, using Tycho Brahe's already numerous observations. It was here that he published his findings in 1610 in Astronomia Nova, in which he described planets moving in elliptical orbits with the Sun occupying one of the two foci (Kepler's first law), and that planets move faster nearer the Sun with the radius vector of each planet (the vector from the Sun to the planet) sweeping out equal areas in equal times (Kepler's second law). His third law was published in 1619 and describes the link between the periods (revolutions) of the planets and their distances from the Sun. Using these laws, Kepler published the first modern astronomical tables in 1627, allowing astronomers to predict the positions of the planets in the future, the past and present. Kepler was an extraordinary scientist whose laws and work were to influence other great scientists such as Newton. His three laws overturned the 2000 year tradition that planets moved in circular orbits about the Sun, and this provided a basis for our further understanding of the solar system. A year after his death, his book Somnium (the dream) was published: it is regarded by many as the first science fiction story.
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