1617 words - 6 pages

Johannes Kepler was a German astronomer and mathematician who lived between 1671-1630. Kepler was a Copernican and initially believed that planets should follow perfectly circular orbits (“Johan Kepler” 1). During this time period, Ptolemy’s geocentric theory of the solar system was accepted. Ptolemy’s theory stated that Earth is at the center of the universe and stationary; closest to Earth is the Moon, and beyond it, expanding towards the outside, are Mercury, Venus, and the Sun in a straight line, followed by Mars, Jupiter, Saturn, and the “fixed stars”. The Ptolemaic system explained the numerous observed motions of the planets as having small spherical orbits called epicycles (“Astronomy” 2). Kepler is best known for introducing three effectual, applicable and valid laws of planetary motion by using the precise data he had developed from Tycho Brahe, a Danish astronomer, which helped Copernicus’s theory of the solar system gain universal reception (“Johan Kepler” 1). Nevertheless, he had made further effective contributions in the field of astronomy, which are valid to society and were used to change how the universe was perceived.

Johannes Kepler moved to Prague in 1600 where he worked as an assistant for Tycho Brahe, and eventually as the imperial mathematician to Rudolf II. Brahe allowed Kepler to see no more than a division of his capacious records. Brahe appointed Kepler the job of understanding the orbit of the planet Mars, which was predominantly difficult. Ironically, it was specifically the Martian data that permitted Kepler to devise the correct laws of planetary motion. Kepler was obliged eventually into the comprehension that the orbits of the planets were not the circles claimed by Aristotle and assumed indirectly by Copernicus, but were instead the “flattened circles” called ellipses. After Brahe’s death, Kepler obtained his data and used it to develop the understanding that the orbits of the planets were ellipses to create his Three Mathematical Laws of Planetary Motion that describe the motion of planets in the Solar System. His first law states, “The orbits of the planets are ellipses, with the Sun at one focus of the ellipse.” As shown in Figure 1, The Sun is not at the focus of the ellipse, but is instead at one focus [usually there is nothing at the other focus of the ellipse]. The planet then trails the ellipse in its orbit, which implies that the Earth-Sun distance is continually changing as the planet goes around its orbit. Kepler’s second law states, “The line joining the planet to the Sun sweeps out equal areas in equal times as the planet travels around the ellipse.” As shown in Figure 2, an imaginary line from the center of the sun to the center of a planet sweeps out the same area in a given time. This means that planets move faster when they are closer to the sun. Kepler’s third and final law states, “The time taken by a planet to make one complete trip around the sun is its period. The ratio of the squares of...

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