Johannes Kepler was born the 27th of December 1571, in Wyl near Stuttgart (in present-day Germany). His mother, the daughter of an innkeeper, was a clever person with a strong presence, a sharp tongue and quarrelsome nature, a personality that almost got her  burned as a witch in her old age.  His father was a quarrelsome and restless mercenary, something of a drunkard, but nevertheless a respected man who disappears without a trace in 1588 during a military campaign. 

Kepler was a sensitive and sickly child and grew up to be a man whose poor health plagued him throughout his life.  He also was near-sighted and sometimes saw double. Despite his poor health (or perhaps because of it), he turned out to be an intense, determined, competitive, temperamental spirit. 

In 1575, the family moved from Wyl to the nearby town of Lowenberg where he went to grammar school and learned reading, writing and latin.  When not in school, he was a helper at a local inn till age12. In 1584, he was admitted at the protestant cloister school of Adelberg. 

In 1587, with the help of  a scholarship, he enters  the protestant university at Tubingen, inyent on studying theology. From 1587 to 1589, while waiting admission to the college of  theology, he spends two years in the study of the liberal arts, including Latin, Greek, Hebrew, dialectics, rethoric, music, mathemathics, geometry and astronomy. (His astronomy teacher was Maslin, a staunch Copernican). In 1589 he is finally admitted in the college of theology. He receives his baccalaureate in 1590 and in 1591, he receives his masters. In 1593, Kepler gives up his religious career, and in March 1594, the 23 year old is sent by the Universiy of Tubingen to the cathedral school of Graz.  The reason he is sent away by the university, is because he is an embarassment to the institution. He keeps defending the Copernican model of the Solar System, a point of view that had been condemned by Luther himself because Luther maintained it contradicted the scriptures. 

Kepler at Graz  1594-1600
In April 1594, after a 20 day walk!, he arrives at Graz where his duties are to teach mathematics and to produce annual calendars complete with astrological prognostications.  While he despises astrology, it nevertheless brings in money. He even makes somewhat of a reputation for himself by correctly predicting two major events: a turkish invasion of the empire and a cold spell.  At Graz, he teaches astronomy (specifically the Copernican system) to classes so small that eventually he has to teach latin and rethoric as well just to fulfill his contract. It is during this time that he studies mathematics. In July1595, while drawing a figure on the blackboard for his students, he has a great insight.  He realizes that there is a relationship between geometry and the patterns of the universe. He sees a way to interlock the five regular solids in such a way that the regular spheres which surround these solids correspond to the distances of the planetary orbits.   He sends the manuscript of this “discovery” to Tubingen where it is published in 1596.  As a consequence of this publication, he becomes well known among astronomers and begins corresponding with Brahe and Galileo. 

During this time also, he courts and marries a young widow, Barbara. All of these events take place against the backgroung of religious struggle between the protestant reformation and the catholic counter-reformation.  While he is teaching in Graz, catholics come back into power, and protestants are expelled (Sept. 1598). Even though Kepler was specifically exempted from the expulsion edict, there nevertheless is enough pressure applied that he leaves to assist Brahe in Prague some two years later. 

Kepler in Prague 1600-1612
While Brahe had attacked and refuted Kepler’s work on the solids, he had nevertheless been impressed by Kepler’s astronomical and mathematical abilities and convinced him to come to Prague.(At the time, Brahe was attached as Court Mathematician to Emperor Rudolph II who had a great interest in astrology.)  Brahe hoped that Kepler would be able to derive planetary motions from the decades of observations hat he, (Brahe) had made, and to prove that the planetary system he had invented was superior to that of Ptolemy or Copernicus. 

Kepler arrived in Prague, the capital of the Holy Roman Empire in February 1600.  As his first task, Brahe assigned him the study of the orbit of  Mars. They worked together for only 15 confrontational, often stormy months before Brahe died in October 1601. Thus, at the age of 30, Kepler (a protestant) became the Imperial Mathematician (November 1601). 

As court mathematician, he was charged by Rudolph II to continue Brahe’s work. (Brahe had been charged with calculating new astronomical tables to replace the out of date Alphonsine and Prutenian tables.) Rudolph was a great supporter of the arts and sciences and was extremely important to Kepler’s work because he provided an atmosphere where intellectual freedom flourished regardless of religion. It is worth noting that Rudolph was much less free with his money and was all too often behind in paying the salaries he promised. 

After some difficulties in obtaining Brahe’s journals from his heirs, and lengthy calculculations, he came to the conclusion that the basic assumption made in all astronomical models from the Greeks on was wrong: planets do not move at constant velocity in circular orbits. Although small, the differences between Brahe’s observations and circular theory were simply too great to be dismissed as observational errors. For Kepler, any theory must agree with the truth of observation of nature. The work on the orbit of Mars was completed in 1606 and published in 1609.  It contained Kepler’s first two laws, that of the ellipses and that of equal areas. As a result he was made a member of the Academia del Lincei. 

Kepler also studied optics. Astronomia pars optica, (1604), included tables of refraction, a way of calculating longitudes between two places by means of eclipses and the inverse square law of illumination. He is the first to realize that the tails of comets are matter expelled from the body of the comet and illuminated by the sun. 

In the Dioptrice, (1611) he gave the fist correct western theory of how the eye sees; clarified how images were formed by lenses, i.e. the theory of telescopes, and developed the theory for eyeglasses By comparing the refraction of light in air and water, the concluded that air was made of matter which has weight. 

The years in Prague were not easy ones. He was often sick and the emperor often did not pay him. On top of his official work, he also had to satisfy the astrological interest of the emperor and other people at the court. Nor was his marriage a happy one. 1611 was an especially bad year for Kepler. His wife and one of his children died and his patron Rudolph II abdicated. The following year, with the death of Rudolph II, and after 12 years in Prague he decides to accept the post of Provincial Mathematician of the Protestant Diet in the town of Linz where he arrives in April 1612. 

Kepler’s years in Linz 1612-1626
In 1613, the new emperor confirms him as Imperial Mathematician and appoints Kepler to the calendar reform commission in Regensburg. Kepler also decided to set up a new household and (choosing from among 11 women) married  Suzanne. It was a much more happy marriage than the first and they had seven children together. As a result of his concern about whether wine barrels actually contained the correct amount of wine, he caculated the volume of wine barrels by approximating it with truncated cones; This would lay the foundation for all later work on conic sections. 

Although he never wanted to be, he was dragged into religious controversies. His refusal to sign the concordat got him excommunicated  and cost him the chair of Mathematics at Tubingen. In 1616, when Kepler was offfered a mathematics chair in Bologna, he refused, stating that his outspokeness would not fit in with the attitudes of certain italians, a clear reference to the attacks on Galileo. 
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In 1617 his mother is put on trial as a witch. For the next 4 years he will have to take time out from his work to try to save her. It’s not until 1621 when he personally appears at his mother’s trial that he succeds in getting her released (she will die 6 months later at the age of nearly 80).  Between 1618-1622 he publishes a book on astronomy and physical sciences for the less well educated. The book contains the notion that it is a force from the sun that moves the planets rather than the planets moving under their own power.  In 1618, he discovers the third law of planetary motion and publishes it in the De Harmonice Mundi(1619). In it, he also brings up for the first time a question that has been debated at length since, namely what is the responsability of the scientist to humanity. 

The last years: 1626-1630
By 1626, he had prepared the great Rudolphine tables but, because the town was embroiled in the 30-year War, he left Linz with his wife, five kids, and books to have the tables printed in Ulm, where they were finally printed in Sept 1627. In January 1628, he appears at the court to hand the emperor his tables.  The emperor makes him a generous money offer on condition the he convert to catholicism. Kepler refuses. 

In the Spring of 1628, he accepts the post of  Mathematician to Wallenstein, Duke of  Sagan in Silesia. Persuaded by an offer to have his own printing presses, he intends to publish the Ephemerides and Tycho Brahe’s journals. He arrives in July 1628. The printing presses arrive by the end of 1629 and in 1630 he publishes the Ephemerides.  During this time he also writes the first science fiction book in which he imagimes a trip to the moon (published after his death in 1634). In an attempt to improve his fiscal situation, having been told by Linz that they would make good on past obligations, he decides to go back there. On the way, he decides to travel to Regensbourg and talk to the emperor directly to see if the emperor will make good on some of the money he had promised. He arrives there on the 5th of November 1630, a sick man and dies there on the 15th of November 1630. 
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