Johannes Kepler (1571 - 1630)

Johannes Kepler was born on December 27, 1571, in the town of Weil der Stadt, a few miles west of Stuttgart. His family spoke German, but there was no Germany at that time. Instead, the town was a free imperial city under the Holy Roman Empire, which ruled over much of Europe from the Middle Ages until the time of Napoleon Bonaparte. Kepler's family were relatively prominent. His grandfather had been mayor of the town, but they were also quite poor by the time Kepler was born. His father Heinrich was a mercenary and disappeared when Kepler was five years old, possibly after he was killed in the Netherlands during the Eighty Years' War. His mother Catherine earned a little money as a healer and a herbalist. Kepler would work this detail into the Somnium, and it may have contributed to the later charges of witchcraft against her. Kepler took an interest in the heavens at an early age. At six years old, he saw the Great Comet of 1577, which was also observed throughout Europe by many famous sky watchers of the time. After attending schools and a Protestant seminary a few miles from his family home, Kepler became a student at the nearby University of Tübingen. There he studied philosophy and theology and became known as an excellent mathematician. He also became known as a skilled astrologer by casting horoscopes for fellow students. This was a common money earner for sky watchers at that time, although Kepler would later write that it didn't make much sense. It was while at Tübingen that Kepler studied the Ptolemaic model of the universe, which stated that the Earth was at the center of the heavens, and the sun, planets and stars rotated around it. But he also learned about the relatively new Copernican model, which suggested the sun was at the center of the orbiting planets, which included the Earth. The Ptolemaic model was developed by the Hellenistic astronomer Claudius Ptolemaeus in the 2nd century, and it was based on the theories of the ancient Greek philosopher Aristotle. It fixed the Earth at the center of a perfect and unchanging universe, and in Kepler's time it was the model insisted on by most scholars and religious authorities. But Kepler favored the new Copernican model, which placed the sun, not the Earth, at the center of the planets. It had been developed less than 100 years earlier by Nicholas Copernicus, a mathematician and astronomer employed as a church official in the Warmia region of Poland. Copernicus found the Ptolemaic system unfeasible, and he constructed a model of the universe where the Earth and other planets circled the sun. The new theory was initially popular, but by Kepler's time it was seen as a religious challenge to Christian scriptures. Kepler, however, became a supporter of the Copernican model while at Tübingen, and he remained so throughout his life. The astronomy lesson at the core of the Somnium seems to have been drafted at this time. Although he'd hoped to become a Protestant minister after graduating, Kepler instead became a teacher of mathematics and astronomy at a school at Graz in Austria. He taught there for several years, and in 1597 published Mysterium Cosmographicum. The Mysteries of the Cosmos, a compilation of ideas he'd thought about while a student at Tübingen. In it he proposed that the distances between the planets could be explained by nested spheres created at the points of platonic solids. The tetrahedron, the cube, the octahedron, the dodecahedron, and the icosahedron. The theory turned out to be entirely incorrect, but it showed his attempts to find mathematical relationships in the heavens. Kepler began writing letters to notable astronomers to whom he'd sent copies of Mysterium Cosmographicum, including Nicolaus Ramus, known as Ursus, who was the official mathematician for the Holy Roman Emperor. Although Ursus didn't reply to Kepler's correspondence, he published a flattering letter from Kepler in a dispute with the Danish astronomer Tycho Brahe. The dispute was about who had developed what became known as the Tychonic model. This was a compromise between the Ptolemaic model and the Copernican model. It still had the Earth at the center, where it was circled by the Sun and the Moon. But the other five planets now revolved around the Sun. The dispute led to Tycho writing to Kepler, among other things to criticize his interpretations of Copernicus, and their correspondence grew from there. Eventually, in 1599, Tycho invited Kepler to visit him in Prague, where he'd started working for the Emperor Rudolf II, and so Kepler traveled to Prague to be Tycho's associate. When Tycho died unexpectedly in 1601, Kepler succeeded him as imperial mathematician. The next 11 years as the official mathematician to the Holy Roman Emperor were the most productive of Kepler's life. His duties mainly involved casting astrological horoscopes for the Emperor and foreign leaders, but he was able to pursue his own astronomical interests, which gave him contact with other prominent scholars. In 1604, Kepler observed a new star, which has since been found to be a supernova and which has been named after him. In 1606, he published a book about his observations called De Stella Nova. In it, he argued that the new star showed the heavens could not be unchanging, as the Ptolemaic model presumed. In 1609, Kepler published one of his greatest books, Astronomia Nova, which included two of his three laws of planetary motion. In it, he introduced the idea that planets orbited the Sun on a path through space, rather than as fixtures on an invisible planetary orb. Using Tycho's observations, he determined the points where Mars and the Earth are at their closest and furthest from the Sun. That led to his famous second law of planetary motion, that orbiting planets sweep out equal areas of space in equal time. His first law, meanwhile, he derived from Tycho's observations of the motions of Mars. He knew that the orbits of planets couldn't be true circles, so he tried other shapes and finally hit on the solution of an eclipse. That led to his famous first law, that all planets move in eclipses, with the Sun at one focus. Kepler's third law, which relates each planet's distance and the time they take to complete one rotation, wasn't published until 1619, in his book called Harmonices Mundi, or the Harmony of the World. He noted all the planets had the same ratio of the square of their orbital period and the cube of an axis of their elliptical orbit. Kepler's observation would be explained by the English scientist Isaac Newton, writing almost 70 years later, as a consequence of the force of gravity. And that led, in turn, to the modern scientific understanding of the universe. Around 1611, Kepler distributed a version of a manuscript that would eventually become although it probably originally didn't have that title. The book was never published in his lifetime, but Kepler rewrote the Somnium over the next 20 years, adding the framing dream sequence that gives it its name and footnotes to explain his references. He wrote in the footnotes that his adventurous tale of witches and demons had been deliberately misconstrued to accuse and jail his elderly mother of witchcraft. The accusations took several years to refute. In 1611, Kepler moved to the city of Linz in Austria, where he remained the imperial mathematician and also taught at a school. In 1627, Kepler completed the Rudolfine tables, which were a catalogue of star and planet positions that used the observations of Tycho Brahe. The tables had been commissioned by the emperor Rudolf, hence their name, but the publication led to disputes with Tycho's numerous relatives, who hoped to profit from it. In 1630, Kepler set out from Linz to the city of Regensburg in Bavaria, where he hoped to collect interest on some money he'd loaned. But he became sick with a fever a few days after his arrival, and died there just over a month later, on 15 November 1630. Kepler's body was buried in a Protestant churchyard in Regensburg, but all the graves there were destroyed a few years later, during the Thirty Years' War.