by The Galileo Project Development Team 
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1. Dates 
Born: Weil der Stadt, Germany, 27 Dec. 1571 
Died: Regensburg, 15 Nov. 1630 
Dateinfo: Dates Certain 
Lifespan: 59 
2. Father 
Occupation: Soldier 
Common soldier of fortune. 
3. Nationality
Birth: Weil der Stadt, Germany 
Career: Germany 
Death: Regensburg, Germany 
4. Education
Schooling: Tübingen, M.A. 
1579, German and Latin Schreibschule, Leonberg. 
1584, Adelberg monastery school (lower seminary). 
1586, Maulbronn, a prepatory school for the university of Tuebingen (higher seminary). 
1587, matriculated Univ. of Tuebingen, but the Stift, the seminary for scholarship students was full, so he stayed at Maulbronn for another two years. 1589, taken into the Stift. 
1588, passed Baccalaureate exam. 
1591, M.A., Tuebingen. He began the theology course, but was called away to Graz in second year. 
5. Religion 
Affiliation: Lutheran 
6. Scientific Disciplines
Primary: Astronomy, Optics, Mathematics 
Subordinate: Astrology 
7. Means of Support 
Primary: Schoolmastering, Patronage 
Secondary: Per (From Wife), Astrology, Calendars 
Education: After passing competitive Wuerttemberg state examinations he entered the school at Maulbronn. In 1589, he entered the Stift as a scholarship student, receiving 6 gulden per year; as a scholarship student he was forever bound into ducal service. In addition, his maternal grandfather granted him the income from a meadow. 
Graz: 1594, teacher of mathematics at the Lutheran Stiftschule at Graz. He earned a salary of 150 gulden (his predecessor had received 200), which was raised to 200 after his marriage, and was granted 60 gulden moving expenses. 
The job of district mathematician and calendar maker was later added to his duties. He made 5 calendars in all; for the first he received an honorarium of 20 gulden (no information on the others). 
He also received income doing astrological nativities and prognostications for lords. 
1597, married the reasonably wealthy two-time widow, daughter of a wealthy mill owner, Barbara Mueller. Her wealth was tied up in land, and was sufficient, Kepler reckoned, to support him after a few years. Her holdings included 10,000 gulden from which Kepler received 70 gulden for maintenance, the yield of a vineyard, and a house. 
Unfortunately, it was difficult to liquidate her assets when Kepler was forced to leave Catholic Graz summarily in 1598, especially because it became illegal for Protestants to lease to Catholics. He was allowed to return, but sought other employment, working for a few months with Tycho Brahe, but then returning shortly to Graz before being banished altogether in 1600. Upon his ultimate expulsion, he was dismissed from his job, paid a half-year's salary, and provided with a letter of recommendation. His exit tax was lowered to 5% from 10%. 
1600, went to work for Tycho Brahe in Prague, until Tycho died and Kepler assumed his position. 
1601, Imperial Mathematician to Rudolf (500 gulden salary). 
Barbara inherited about 3000 gulden of landed property from her father in 1603. She died in 1611, leaving no will and consequently he got nothing, except for 2000 gulden for her children which he invested (1615) in the treasury of the Upper Austrian representatives. 
Rudolf abdicated in 1611. In 1612, he died, freeing Kepler to leave Prague. 
1612-1628, district mathematician and teacher in Linz (to which was added the task of completing a map of Upper Austria, which he later had removed). He received a salary of 400 gulden (plus travel expenses for the map). (In late 1616, after a political battle over whether he ought to be retained, he was granted a small honorarium as a consolation for the insult.) 
1613, he married an orphan, Susanna Reuttinger, a ward of Baroness Elizabeth von Starhemberg. 
While in Linz, Kepler again supplemented his income with proceeds from calendars. For instance, he paid for the publication of the ephemeredes of 1617 with a calendar for 1616. In all, he made six popular calendars between 1617 and 1624. 
Kepler was allowed to stay on in Linz after the expulsion of the Protestants in 1626, and even retained his position despite a prolonged absence from 1626-1628. 
1612, Emperor Matthais continued the post of Imperial Mathematician at reduced salary of 300 fl/yr plus 60 gulden for dwellings and wood costs. and gave his consent for Kepler to move to Linz. 
Ferdinand continued Kepler's appointment as imperial mathematician until Kepler's death. 
1628, moved to Sagan to work for Albrecht von Wallenstein, at a salary of 1000 gulden, and a press, for which Wallenstein promised to provide twenty bales of paper and 1,040 gulden printing costs annually. 
In 1630, the congress of electors dismissed Wallenstein. Kepler tried to return to Linz, to collect on two 6% bonds (2000 and 1500 gulden), but died en route. 
8. Patronage 
Types: Scientist, Court Official, Aristocrat, Government Official 
Education: After Landesexamen in 1583, Kepler got a scholarship from the Duke of Wuerttemberg; this scholarship bound him forever into ducal service. In 1590, the magistrate of Weil proposed him to the senate of the university of Tuebingen for a stipend of 20 gulden per year, which was granted. The senate renewed it in 1591. The senate then recommended him for the post of teacher of mathematics to the protestant school at Graz. 
Graz: For moving to Graz, Kepler received a loan of 50 gulden from Prof. Gerlach, the superintendent of the school; Kepler was later granted 60 gulden moving expenses. The commissioners of the school upon the occasion of his wedding granted him as a "veneration" a silver cup worth 27 gulden. Kepler requested and received from the commissioners a raise to a 200 gulden salary after his wedding. 
He was sought out by Lords to do nativities and prognostications with which he supplemented his income. (Include this under Miscellaneous). 
The city granted him a honorarium of 20 gulden for his first calendar. The city was generally kind to him; after the expulsion of Protestants he was given a half-year's salary and a letter or recommendation. 
In 1596, he visited the Duke of Wuerttemberg and presented him with the idea of an artistic representation of his system of nested spheres from the Mysterium which he wanted to dedicate to the Duke. He later applied to Duke Johann Friedrich of Wuerttemberg for a job, but was rejected because he was suspected of being "a sly Calvinist." 
The Duke of Wuerttemberg later arranged that the court documents of Kepler's mother's trial be sent to Tuebingen for the decision of the legal faculty (in which Kepler had a contact, Christoph Besold), and he was responsible for the order that she be absolved and the charges dismissed. 
The Mysterium was dedicated to the estates of Styria, from whom Kepler received a 250 gulden honararium in 1600. 
After the general expulsion order for Protestant teachers in 1598, archduke Ferdinand made an exception in the case of Kepler, allowing him to continue as district mathematician. Kepler attributed his favor at court to the regimental counsellor Manechio. Ferdinand also rewarded Kepler for an astronomical essay Kepler addressed to him in 1600. After the expulsion of all Protestants, Ferdinand ordered Kepler be reimbursed his 5% exit tax, but this was never carried out. 
As emperor, Ferdinand confirmed him as imperial mathematician, and again excepted him when expelling non- Catholic teachers. Ferdinand also finally wrote drafts to pay him some of his back pay to finance the publication of the Rudolfine Tables, which was eventually dedicated to him. 
Ferdinand approved Kepler's move to Ulm in 1626. 
He received Kepler graciously in Prague in 1627, awarding him 4000 gulden (in drafts) for dedication of the Rudolfine Tables. He could have stayed in service, but would have had to become Catholic. 
Even as Kepler lay dying the Emperor sent a gentleman with 25 or 30 Hungarian ducats to his aid. The Emperor owed 12,694 gulden to his family in 1633. Though claims continued to be made up until 1717, this money was never paid. 
At the end of his life Kepler called himself Duke of Friedland. I do not know why. Presumably he received the title from Wallenstein or Ferdinand (perhaps given the title after Wallenstein's downfall?). 
The Bavarian chancellor Herwart von Hohenburg was a major patron to Kepler. They corresponded and H.v.H. lent Kepler books, which he did not have. H.v.H. was probably partly responsible for Kepler's permission to stay in Graz (see directly above). 
Kepler appealed to Michael Maestlin often as though to a patron, for instance asking around for a job in 1600, but Maestlin seldom was able to oblige him. 
1600, Tycho supported him in Prague. Kepler moved very much in the orbit of Tycho, including living in the same house from the beginning of 1601. Tycho assigned Kepler the task of refuting Ursus. 
1601, Kepler became Imperial mathematician to Rudolf II. He had tremendous trouble getting paid his 500 gulden salary. At one point, the Emperor paid 400 gulden in printing costs, which Kepler spent on household expenses, he then granted an additional 500 gulden for which he reserved the entire edition of Astronomia nova for himself (Kepler eventually had to sell the entire edition to the printer). 
He often gave extra compensation, such as a draft for 2000 talers in 1610, on which Kepler could not collect. 
Kepler dedicated numerous works to the Emperor, including the Astronomia nova, Astronomiae pars optica, and De stella nova. He also prepared numerous reports for the Emperor on astrological or scientific matters. 
After abdicating, Rudolf asked Kepler to stay on, which he did, until the Emperor's death. 
By March 1611, he was 3000 gulden in arrears. 
Casting about for another job, Kepler presented a copy of the Astronomiae pars optica to Duke Maximilian of Bavaria. The Duke's gift to Kepler was so small that Herwart von Hohenburg increased it out of his own pocket. 
Elector Ernst of Cologne sometimes occupied days of his time at court, and lent him a telescope. 
Kepler presented him with the manuscript of Dioptrice. 
Baron Johann Friedrich Hoffman von Gruenbueehel und Strechau, an imperial advisor, housed Kepler when he first visited Prague, and later provided Kepler with two instruments built on Tychonic designs. 
Kepler dedicated his first work after leaving Prague to Peter Wok von Rosenberg, the leader of the Utraquist faction and one of the richest and most powerful families in Bohemia. 
Kepler exchanged letters with Wenzeslaus Budowetz, a Czech aristocrat. 
Kepler had allies in two court advisers: Johannes Barwitz, who helped Kepler in his fights to get paid; and Johannes Matthaeus Wackher von Wackenfels, to whom Kepler dedicated an essay on snowflakes. 
Johannes Jessenius, a distinguished anatomist at the Univ. of Prague and a friend of Kepler, sponsored him at his first meeting with Tycho, and later when rector (1617) he contemplated hiring Kepler. 
Kepler was a frequent guest of the imperial councilor Johannes Polz. 
Johann Georg Goedelmann, the ambassador to the electorate of Saxony, took over as godfather to Kepler's son. 
Kepler was a friend of Johannes Pistorius, father confessor and adviser to Rudolf II, to whom Kepler had to report. 
He dedicated a copy of De stella novis to King James I. Kepler was also going to dedicate the Harmonices Mundi to James I. In 1620, the English ambassador, Sir Henry Wotton, visited him and invited him to England. 
In a vain attempt to collect on the 2000 taler draft, Kepler dedicated Eclogae Chronicae to Tobias Scultetus, an imperial advisor, who had been appointed fiscal procurator in Silesia. 
Previous to the Kepler's application to become mathematician in Linz, he had been invited to come to Linz by Austrian Lords, such as Helmhard von Joerger. 
Linz Patrons: Baron Erasmus von Starhemberg and Georg Erasmus von Tschernembl, the Protestant leaders of Upper Austria; the Lords von Polheim, Maximilian von Liechtenstein and Helmhard von Joerger. 
Emperor Matthias, who succeeded Rudolf, continued Kepler's position and paid Kepler 400 gulden for finishing the Rudolfine Tables etc. 
After Magini's death Giovanni Antonio Roffeni, prof. of philosophy at Bologna, offered Kepler the job, but he declined. 
The representatives of Upper Austria were Kepler's major patrons in Linz. There was an occasion in 1616 when Kepler became the object of a political fight among the representatives, with the Lords facing off against the knights and the Lords prevailing on Kepler's side (see above). The representatives presented him with a goblet worth 40-50 gulden on the occasion of his second marriage. Kepler presented Stereometria to the reps., who granted him 150 gulden. The Epitome is dedicated to them as well. In 1628, the representatives paid him 200 gulden for the presentation of the Rudolfine Tables, paid his traveling expenses, and gave their consent to be dismissed. Kepler dedicated the ephemerides of 1621-1629 (1630) to the representatives. 
Kepler's best friend for almost twenty years was the Strasburg humanist and noble Matthias Bernegger, to whom Kepler appealed on occasion for a job. 
Kepler produced a belated dedication sheet for the Harmonice mundi (1620) to Frederick V of the Palatinate, the winter-king and son-in-law of James I, whom Kepler saw as a great hope in matters of creed. 
The printing of the Epitome was subsidized by Abbot Anton von Kremsmuenster, president of the prince's private exchequer and previous member of the representatives of Upper Austria. He helped Kepler in his effort to use some of the money still owed him by Rudolf to finance the publication of the Rudolfine Tables. 
The book on logarithms (1624) is dedicated to Landgrave Philip of Hesse-Butzbach, who had it printed in Marburg. Later, when visiting the Landgrave at Butzbach, he had been attracted by the instruments and facilities. Landgrave Philip was willing to use his influence with Landgrave Georg to whom Kepler and submitted a petition for interim employment (1627) and had asked to use his influence with the Duke of Wuerttemberg. Georg offered him a house in Marburg and support should the emperor dismiss him. 
The imperial vice-chancellor, Baron Ludwig of Ulm intervened for Kepler at one point in Kepler's attempt to get paid. 
Count von Herbersdorf, president of the Bavarian district, succeeded in getting permission for Kepler to hire printers regardless of creed after the Protestants had been expelled from Linz. 
Kepler was assisted to remove the seal of the reformation commission on his library by the Jesuit Father Paul Guldin in Vienna (he wanted to borrow some of the books under seal). 
In Ulm (1626) Kepler had friends in Gregor Horst, previously professor of medicine in Wittenberg and Giessen and physician- in-ordinary to Landgrave Ludwig of Hesse, with whom he stayed; and Johann Baptist Hebenstreit, rector of the gymnasium, who looked after the bales of paper Kepler had purchased for the Rudolfine Tables. 
Albrecht von Wallenstein, imperial General-colonel- commander-in-chief and General of the Baltic and oceanic seas, and holder of the duchies of Friedland and Sagan, was Kepler's last major patron. An avid believer in astrological prognostication, he had requested an anonymous nativity from Kepler as early as 1608 (though Kepler knew who it was), and had asked for an update in 1624. He returned an honorarium and a promise of "princely favors" for whenever Kepler would be in need of them. His most attractive feature to Kepler was his belief in the peaceful co-existance of creeds, but in 1628 all citizens of Sagan were ordered to become Catholic or leave, though Kepler and his printers were again excepted. Kepler dedicated the ephemerides for 1629-1639 (1630) and a short work in reply to the Jesuit Johannes Terrentius (1630) to Wallenstein. 
Philip Mueller, professor at Leipzig, with whom Kepler corresponded, was able to get Kepler a press that he could take to Sagan. 
Dr. Thomas Lindemann, rector of the University of Rostock called Kepler to the university (1629). Before taking the job Kepler demanded that Wallenstein get him released from imperial service and get him the 11,817 gulden he was still owed by the Emperor (he probably didn't really want to go). 
9. Technological Involvement 
Types: Hydraulics, Instruments, Applied Mathematics 
Kepler erected an instrument in Graz to observe a solar eclipse. 
He designed a model of the nested spheres, which never got completed. He also designed a small fountain based on a valveless pump, which he had Joost Buergi construct and then presented to the Emperor. 
Part of his duties in Linz was to be the completion of a map of Upper Austria. I am not aware that he actually did this. 
In 1613 Kepler was ordered by the Emperor to Regensburg to assist in the debate about the reform of the calendar. 
In Ulm, Kepler was asked to help in the regulation of the town's weights and measures. He solved the problem in a lengthy essay and designed a new regulatory measuring basin. 
To his work on logarithms I add his calculation of the volume of casks. 
10. Scientific Societies 
Memberships: None 
He corresponded with (among others): David Fabricius, Johannes Fabricius, Tycho Brahe, Michael Maestlin, Longomontanus [Severin], Thomas Harriot. 



1.Max Caspar, Kepler. [QB36.K4C32] 
2.Martha List, "Kepler," Neue Deutsche Biographie, 11 (Berlin, 1977), 494-508. [ref. T1053.N47 v.11] 

Compiled by: 

Richard S. Westfall 
Department of History and Philosophy of Science Indiana University