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Johannes Kepler (1571- 1630)

Johannes Kepler was born in Wüttemburg, in the Holy Roman Empire in 1571. Although his grandfather, on his father's side, had been a craftsman and his maternal grandfather had been an innkeeper and mayor, his father was a mercenary soldier who Kepler considered rough and "without morals". Kepler did not like his mother very much either, which might explain why he lived with his grandparents from 1574 to 1576. However, when his parents moved to Leonburg in 1576, Kepler had to go with them. He first attended a Latin school and later, in 1584 he studied at the Protestant Seminary at Adelberg.

Kepler won a scholarship to go to Tübingen University in 1589. He studied theology and was, at that time, destined for the Lutheran Ministry. He was awarded an MA in 1591 and decided to continue his university studies. His math tutor, Michael Maestlin, introduced his students to Copernicus and his heliocentric theory. He did this outside of his normal teaching periods since the universities were only supposed to teach the geocentric model, as proposed by Ptolemy.

In 1594 Kepler accepted a post at the Lutheran school in Graz, Austria. Here he taught arithmetic, geometry, Virgil and rhetoric. He also became the official mathematician and calendar maker for the Styria district. In 1596 Copernicus wrote a paper called Mysterium Cosmographicum or The Cosmographic Mystery. In it he defended Copernicus and the heliocentric model.

In 1600 Kepler was forced to leave Graz. At that time all Protestants were being forced to sign an allegiance to the Catholic Church. Kepler had rejected religion, previously refusing to declare an allegiance to the Lutheran (Protestant) Church. He found himself without a refuge. Fortunately, Tycho Brahe had invited Kepler to join him in Prague as his assistant. Brahe died just one year after Kepler joined him, and Kepler was offered to take Brahe's place as the Imperial Mathematician. This post was considered the best of its kind in Europe.

Over the next ten years Kepler wrote a number of books and papers. His most famous are Astronomia pars Optica or The Optical Part of Astronomy that discussed the use of lenses in telescopes and explained how the eye functions, and De Stella Nova or About the New Star, about the star he had observed in 1604. Kepler also used Brahe's very accurate data to compete Astronomia Nova or New Astronomy. Kepler was not a good observer himself but, using Brahe's work, he was able to sort out the data and apply his mathematical mind to it. His conclusions are now known as Kepler's First and Second Laws of Planetary Motion. He was the first to apply the scientific method to his research.


Johannes Kepler

© Sternwarte Kremsmünster Observatory


Kepler read about Galileo's use of the telescope and his observations of Jupiter's moons, in 1610. He immediately obtained a telescope and verified Galileo's work. This he published in his book Narratio de Observatis Quatuor Jovis Satellitibus or Narration about Four Satellites of Jupiter Observed. Galileo must have been much relived about the support he had been given by Kepler since, prior to the publication, Galileo was the only person to have seen the Jovian moons and many people did not believe him.

In 1612 Kepler moved to Linz. He had been forced out of Prague by the political situation stemming from the counter-reformation. The Emperor Rudolph II had died and had been replaced by his son, Matthias. Although Kepler had left for Linz he was retained as the Imperial Mathematician. His life was still difficult in Linz but he was a court official and this stopped him being chased out of the region. Even so, he and his family were persecuted by the counter revolutionists. Soldiers had to be deployed to protect him. Eventually, in 1627 the situation became so bad that he moved from Linz to Ulm.

Kepler's personal life was quite tragic. Apart from having to move so often to escape persecution, his first wife died in 1612. The two children from the marriage had both died young. Kepler's mother was accused of witchcraft and he had to travel to Wüttemburg very often to defend her, which he did successfully. He married for a second time and the couple had six children, only three of whom survived. It is amazing that Kepler was able to keep writing during these times. In 1619 he published Harmonice Mundi or Harmony of the World that gave the world Kepler's Third Law of Planetary Motion. Between 1617 and 1621 he published Epitome Astronomiae Copernicanae or Epitome of Copernican Astronomy, a book that became a very important explanation of the heliocentric theory.

He also managed to complete the Rudolphine Tables, a publication that had been started by Tycho Brahe. Just before Brahe died, Kepler had promised him that he would finish this book. It took a long time to get published because Kepler had to have permission from the Brahe family members, but it eventually went to print in 1627. It was an extremely important book because it enabled the user to calculate the position of the planets, both in the past and at any time in the future, with accuracy.

In 1628 Kepler moved once more, this time to Sagan where he had been invited by Count Albrecht Von Wallenstein. He was penniless and could not find work. He decided to go to Prague to try to collect money that he was owed by the Emperor from the time when he had been the Imperial Mathematician. This amounted to over 1100 gulden. Kepler died in Regensburg in 1630, on the journey to Prague.


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