View source for Johannes Kepler

{{Short description|German astronomer and mathematician}}
{{Redirect|Kepler}}
{{Featured article}}
{{Pp-pc}}
{{Use dmy dates|date=November 2025}}
{{Infobox scientist
| name              = Johannes Kepler
| image             = JKepler.jpg
| caption           = Portrait {{circa|1910}}, after 1620 original
| birth_date        = {{birth date|df=y|1571|12|27}}
| birth_place       = [[Weil der Stadt|Free Imperial City of Weil der Stadt]], Holy Roman Empire
| death_date        = {{Death date and age|df=yes|1630|11|15|1571|12|27}}
| death_place       = [[Regensburg|Free Imperial City of Regensburg]], Holy Roman Empire
| field             = {{hlist|[[astronomy]]|[[astrology]]|[[mathematics]]|[[natural philosophy]]}}
| education         = [[Tübinger Stift]], [[University of Tübingen]] ([[Master of Arts|MA]])<ref>{{cite SEP |last=Liscia |first=Daniel A. Di |title=Johannes Kepler |url-id=kepler}}</ref>
| doctoral_advisor  = [[Michael Maestlin]]
| known_for         = {{Plain list|
* [[Kepler's laws of planetary motion]]
* [[Kepler conjecture]]
* [[Kepler's equation]]
* ''[[Rudolphine Tables]]''
}}
| signature         = Unterschrift Kepler.svg
}}
{{Classical mechanics}}
{{Cosmology|scientists}}

'''Johannes Kepler'''{{efn|English: {{IPAc-en|ˈ|k|ɛ|p|l|ər}} {{respell|KEP|lər}},<ref>[http://www.dictionary.com/browse/kepler "Kepler"]. ''[[Random House Webster's Unabridged Dictionary]]''.</ref> {{IPA|de|joˈhanəs ˈkɛplɐ|lang|De-Johannes Kepler.ogg|small=no}}.<ref>{{cite book|author1=Dudenredaktion|last2=Kleiner|first2=Stefan|last3=Knöbl|first3=Ralf|year=2015|orig-year=First published 1962|title=Das Aussprachewörterbuch|trans-title=The Pronunciation Dictionary|url=https://books.google.com/books?id=T6vWCgAAQBAJ|language=de|edition=7th|location=Berlin|publisher=Dudenverlag|isbn=978-3-411-04067-4|pages=487, 505}}</ref><ref>{{cite book|last1=Krech|first1=Eva-Maria|last2=Stock|first2=Eberhard|last3=Hirschfeld|first3=Ursula|last4=Anders|first4=Lutz Christian|title=Deutsches Aussprachewörterbuch|trans-title=German Pronunciation Dictionary|url=https://books.google.com/books?id=E-1tr_oVkW4C&q=deutsches+ausspracheworterbuch|language=de|year=2009|publisher=Walter de Gruyter|location=Berlin|isbn=978-3-11-018202-6|pages=628, 646}}</ref>}} (27 December 1571 – 15 November 1630) was a German [[astronomer]], [[mathematician]], [[astrologer]], [[Natural philosophy|natural philosopher]] and writer on music.<ref>{{cite encyclopedia |last=Jeans |first=Susi |author-link=Susi Jeans |others=Revised by [[H. Floris Cohen]] |year=2013 |orig-year=2001 |encyclopedia=[[Grove Music Online]] |title=Kepler [Keppler], Johannes |publisher=[[Oxford University Press]] |location=Oxford |access-date=26 September 2021 |doi=10.1093/gmo/9781561592630.article.14903 |isbn=978-1-56159-263-0 |url-access=subscription |url=https://www.oxfordmusiconline.com/grovemusic/view/10.1093/gmo/9781561592630.001.0001/omo-9781561592630-e-0000014903 }} {{Grove Music subscription}}</ref> He is a key figure in the 17th-century [[Scientific Revolution]], best known for his [[Kepler's laws of planetary motion|laws of planetary motion]], and his books ''[[Astronomia nova]]'', ''[[Harmonice Mundi]]'', and ''[[Epitome Astronomiae Copernicanae]]''. The variety and impact of his work made Kepler one of the founders and fathers of modern [[astronomy]], the [[scientific method]], [[natural science]], and [[modern science]].<ref>{{cite web | url=https://www.dpma.de/english/our_office/publications/milestones/greatinventors/johanneskepler/index.html | title=DPMA {{pipe}} Johannes Kepler }}</ref><ref>{{Cite web |url=https://www.nasa.gov/kepler/education/johannes |title=Johannes Kepler: His Life, His Laws and Times|publisher= NASA |access-date=1 September 2023 |archive-date=24 June 2021 |archive-url=https://web.archive.org/web/20210624003856/https://www.nasa.gov/kepler/education/johannes/ |url-status=dead }}</ref><ref>{{cite web | url=https://micro.magnet.fsu.edu/optics/timeline/people/kepler.html | title=Molecular Expressions: Science, Optics and You – Timeline – Johannes Kepler|publisher=Florida State University }}</ref> He has been described as the "father of [[science fiction]]" for his novel ''[[Somnium (novel)|Somnium]]''.<ref>{{Cite web|url=https://www.bbvaopenmind.com/en/science/leading-figures/kepler-the-father-of-science-fiction/|title=Kepler, the Father of Science Fiction|date=16 November 2015|website=bbvaopenmind.com}}</ref><ref>{{cite web|url=https://www.themarginalian.org/2019/12/26/katharina-kepler-witchcraft-dream/|title=How Kepler Invented Science Fiction and Defended His Mother in a Witchcraft Trial While Revolutionizing Our Understanding of the Universe|first=Maria|last=Popova|website=themarginalian.org|date=27 December 2019 }}</ref>

Kepler was a mathematics teacher at a [[seminary]] school in [[Graz]], where he became an associate of [[Hans Ulrich von Eggenberg|Prince Hans Ulrich von Eggenberg]]. Later he became an assistant to the astronomer [[Tycho Brahe]] in [[Prague]], and eventually the imperial mathematician to [[Rudolf II, Holy Roman Emperor|Emperor Rudolf II]] and his two successors [[Matthias, Holy Roman Emperor|Matthias]] and [[Ferdinand II, Holy Roman Emperor|Ferdinand II]]. He also taught mathematics in [[Linz]], and was an adviser to [[Albrecht von Wallenstein|General Wallenstein]].

Kepler lived in an era when there was no clear distinction between [[astronomy]] and [[astrology]],<ref>{{cite journal
 | last = Dooley | first = Brendan
 | date = June 2021
 | doi = 10.1515/bthz-2021-0010
 | issue = 1
 | journal = Berliner Theologische Zeitschrift
 | quote = From ancient times through the seventeenth century European astronomy and astrology remained two sides of the same coin
 | pages = 156–175
 | publisher = Walter de Gruyter GmbH
 | title = From astrology to astronomy: renaissance and early modern perspectives
 | volume = 38}}</ref> but there was a strong division between astronomy (a branch of [[quadrivium|mathematics]] within the [[liberal arts]]) and [[physics]] (a branch of [[natural philosophy]]).<ref>{{cite journal
 | last = Omodeo | first = Pietro Daniel
 | date = August 2015
 | doi = 10.1002/andp.201500238
 | issue = 7–8
 | journal = Annalen der Physik
 | publisher = Wiley
 | title = The 'Impiety' of Kepler's shift from mathematical astronomy to celestial physics
 | volume = 527| bibcode = 2015AnP...527A..71O
 | hdl = 11858/00-001M-0000-002A-8F0F-E
 | hdl-access = free
 }}</ref> Kepler also incorporated religious arguments and reasoning into his work, motivated by the religious conviction and belief that God had created the world according to an intelligible plan that is accessible through the natural light of [[reason]].<ref>Barker and Goldstein. "Theological Foundations of Kepler's Astronomy", ''Osiris'', 16, 2001, pp.&nbsp;112–113.</ref> Kepler described his new astronomy as "celestial physics",<ref>Kepler. ''New Astronomy'', title page, tr. Donohue, pp.&nbsp;26–27</ref> as "an excursion into [[Aristotle]]'s ''[[Metaphysics (Aristotle)|Metaphysics]]''",<ref>Kepler. ''New Astronomy'', p. 48</ref> and as "a supplement to Aristotle's ''[[On the Heavens]]''{{-"}},<ref>''Epitome of Copernican Astronomy'' in ''Great Books of the Western World'', Vol. 15, p. 845</ref> transforming the ancient tradition of physical cosmology by treating astronomy as part of a universal mathematical physics.<ref>Stephenson. ''Kepler's Physical Astronomy'', pp.&nbsp;1–2; Dear, ''Revolutionizing the Sciences'', pp.&nbsp;74–78</ref> Additionally, he did fundamental work in the field of [[optics]], being named the father of modern optics,<ref>{{cite journal | url=https://www.sciencedirect.com/science/article/abs/pii/S0960077922008748 | doi=10.1016/j.chaos.2022.112695 | title=Kepler in search of the 'Anaclastic' | date=2022 | last1=Coullet | first1=Pierre | last2=San Martin | first2=Jaime | last3=Tirapegui | first3=Enrique | journal=Chaos, Solitons & Fractals | volume=164 | article-number=112695 | bibcode=2022CSF...16412695C | s2cid=252834988 | url-access=subscription }}</ref> in particular for his ''Astronomiae pars optica''. He also invented an improved version of the [[refracting telescope]], the Keplerian telescope, which became the foundation of the modern refracting telescope,<ref>{{cite encyclopedia | url=https://www.britannica.com/science/Keplerian-telescope | title=Keplerian telescope {{pipe}} Optical Design, Refracting, Astronomy |encyclopedia=Encyclopaedia Britannica }}</ref> while also improving on the telescope design  by [[Galileo Galilei]],<ref>{{cite book |title= Optics|last= Tunnacliffe|first= AH |author2=Hirst JG |date= 1996|location= Kent, England |isbn= 978-0-900099-15-1|pages= 233–237}}</ref> who mentioned Kepler's discoveries in his work. He postulated the [[Kepler conjecture]]. Kepler influenced among others [[Isaac Newton]], providing one of the foundations for his theory of [[Newton's law of universal gravitation|universal gravitation]].<ref>{{Cite journal|last=Voelkel|first=James R.|date=2001|title=Commentary on Ernan McMullin, "The Impact of Newton's Principia on the Philosophy of Science"|url=https://www.jstor.org/stable/3080920|journal=Philosophy of Science|volume=68|issue=3|pages=319–326|doi=10.1086/392885|jstor=3080920|s2cid=144781947|issn=0031-8248}}</ref>

== Early life ==
=== Childhood (1571–1590) ===
[[File:Kepler-Geburtshaus.jpg|thumb|left|upright=0.7|Kepler's birthplace, in [[Weil der Stadt]], Germany]]
Kepler was born on 27 December 1571, in the [[Free Imperial City]] of [[Weil der Stadt]] (now part of the [[Stuttgart Region]] in the German state of [[Baden-Württemberg]]). His parents were Lutheran, but it is presumed that he was baptized a Catholic, as Protestant baptisms were not permitted in Weil at that time.<ref>{{cite book | last1=Osterhage | first1=Wolfgang | title=Johannes Kepler | publisher=Springer | date=2020 | isbn=978-3-030-46857-6 | page=68}}</ref><ref name=Hübner>{{cite journal | last1=Hübner | first1=Jürgen | title=Kepler's praise of the Creator | journal=Vistas in Astronomy | volume=18 | date=1975 | issue=1 | doi=10.1016/0083-6656(75)90113-0 | pages=369–382 | bibcode=1975VA.....18..369H }}</ref> His grandfather, Sebald Kepler, had been Lord Mayor of the city. By the time Johannes was born, the Kepler family fortune was in decline. His father, Heinrich Kepler, earned a precarious living as a [[mercenary]], and he left the family when Johannes was five years old. He was believed to have died in the [[Eighty Years' War]] in the Netherlands where, although a Protestant, he was fighting in the Catholic Spanish army.<ref name=Albinus>{{Cite journal |last=Albinus |first=Hans-Joachim |date=June 2002 |title=Joannes Keplerus Leomontanus: Kepler's childhood in Weil der Stadt and Leonberg 1571&ndash;1584 |journal=The Mathematical Intelligencer |language=en |volume=24 |issue=3 |pages=50–58 |doi=10.1007/BF03024733 |s2cid=123965600 |issn=0343-6993|doi-access=free }}</ref> His mother, [[Katharina Kepler|Katharina Guldenmann]], an innkeeper's daughter, was a [[healer (alternative medicine)|healer]] and [[herbalist]]. Johannes had six siblings, of which two brothers and one sister survived to adulthood. Born prematurely, he claimed to have been weak and sickly as a child. Nevertheless, he often impressed travelers at his grandfather's inn with his phenomenal mathematical faculty.<ref>Caspar. ''Kepler'', pp. 29–36; Connor. ''Kepler's Witch'', pp. 23–46.</ref>

[[File:Von einem Schrecklichen vnd Wunderbarlichen Cometen so sich den Dienstag nach Martini dieses lauffenden M. D. Lxxvij. Jahrs am Himmel erzeiget hat (grayscale).png|thumb|As a child, Kepler witnessed the [[Great Comet of 1577]], which attracted the attention of astronomers across Europe.]]
He was introduced to astronomy at an early age and developed a strong passion for it that would span his entire life. At age six, he observed the [[Great Comet of 1577]], writing that he "was taken by [his] mother to a high place to look at it."<ref name = Koestler234 /> In 1580, at age nine, he observed another astronomical event, a [[lunar eclipse]], recording that he remembered being "called outdoors" to see it and that the [[Moon]] "appeared quite red".<ref name=Koestler234>Koestler. ''The Sleepwalkers'', p. 234 (translated from Kepler's family horoscope).</ref> However, childhood [[smallpox]] left him with weak vision and crippled hands, limiting his ability in the observational aspects of astronomy.<ref>Caspar. ''Kepler'', pp.&nbsp;36–38; Connor. ''Kepler's Witch'', pp.&nbsp;25–27.</ref>

Kepler attended the Grammar School in Weil until 1577, when the family moved to [[Leonberg]] in Protestant [[Duchy of Württemberg|Württemberg]].<ref>{{cite book | last1=Baumgardt ·| first1=Carola| title=Johannes Kepler: Life and Letters | publisher=Philosophical Library | date=1951 | pages=22–27}}</ref> He attended the elementary German school in Leonberg for a year, and then the [[Latin school|Latin Grammar School]], where all lessons and books were in Latin. He was then at two monastic schools, from 1584 in [[Adelberg]], and from 1586 at the [[Evangelical Seminaries of Maulbronn and Blaubeuren|seminary at Maulbronn]].<ref name=Albinus/> In September 1589, Kepler entered the [[Tübinger Stift]] at the [[University of Tübingen]], a seminary which served to prepare Lutheran pastors for Württemberg. There, he studied philosophy under Vitus Müller<ref>Connor, James A. ''Kepler's Witch'' (2004), p. 58.</ref> and [[theology]] under [[Jacob Heerbrand]] (a student of [[Philipp Melanchthon]] at [[Wittenberg]]), who also taught [[Michael Maestlin]] while he was a student, until he became Chancellor at Tübingen in 1590.<ref name="Kepler's Astronomy Author 2001 p. 96">Barker, Peter; Goldstein, Bernard R. "Theological Foundations of Kepler's Astronomy", Osiris, 2nd Series, Vol. 16, Science'' in Theistic Contexts: Cognitive Dimensions'' (2001), p. 96.</ref> He proved himself to be a superb mathematician and earned a reputation as a skillful astrologer, casting [[horoscope]]s for fellow students. Under the instruction of Michael Maestlin, Tübingen's professor of mathematics from 1583 to 1631,<ref name="Kepler's Astronomy Author 2001 p. 96" /> he learned both the [[Ptolemaic system]] and the [[Copernican heliocentrism|Copernican system]] of planetary motion. He became a [[Nicolaus Copernicus|Copernican]] at that time. In a student disputation, he defended [[heliocentrism]] from both a theoretical and theological perspective, maintaining that the [[Sun]] was the principal source of motive power in the universe.<ref>Westman, Robert S. "Kepler's Early Physico-Astrological Problematic," ''[[Journal for the History of Astronomy]]'', '''32''' (2001): 227–236.</ref> Despite his desire to become a minister in the Lutheran church, he was denied ordination because of beliefs contrary to the [[Formula of Concord]], the Lutheran statement of faith which had been adopted in 1577.<ref>{{Cite journal |last1=Barker |first1=Peter |last2=Goldstein |first2=Bernard R. |date=January 2001 |title=Theological Foundations of Kepler's Astronomy |url=http://dx.doi.org/10.1086/649340 |journal=Osiris |volume=16 |pages=88–113 |doi=10.1086/649340 |s2cid=145170215 |issn=0369-7827|url-access=subscription }}</ref> Near the end of his studies, Kepler was recommended for a position as teacher of mathematics and astronomy at the Protestant school in Graz, in [[Styria]], [[Inner Austria]]. He accepted the position in April 1594, at the age of 22.<ref>Caspar. ''Kepler'', pp. 38–52; Connor. ''Kepler's Witch'', pp. 49–69.</ref>

=== Graz (1594–1600) ===
{{multiple image|perrow=1
| image1 = Barbara Müller and Johannes Kepler.jpg
| caption1 = Oil on copper portraits of Kepler and his wife, {{circa|1600}}
| image2 = House of Johannes Kepler.JPG
| caption2 = House of Kepler and Barbara Müller in [[Gössendorf]], near Graz (1597–1599)}}
During his time in Graz (1594–1600), he issued many official calendars and prognostications that enhanced his reputation as an astrologer. Although Kepler had mixed feelings about astrology and disparaged many customary practices of astrologers, he believed deeply in a connection between the cosmos and the individual. He eventually published some of the ideas he had entertained while a student in the ''Mysterium Cosmographicum'' (1596), published a little over a year after his arrival at Graz.<ref>Caspar, ''Kepler''. pp.&nbsp;58–65.</ref>

In December 1595, Kepler was introduced to Barbara Müller, a 23-year-old widow (twice over) with a young daughter, Regina Lorenz, and he began courting her. Müller, an heiress to the estates of her late husbands, was also the daughter of a successful mill owner. Her father Jobst initially opposed a marriage. Even though Kepler had inherited his grandfather's nobility, Kepler's poverty made him an unacceptable match. Jobst relented after Kepler completed work on ''Mysterium'', but the engagement nearly fell apart while Kepler was away tending to the details of publication. However, Protestant officials—who had helped set up the match—pressured the Müllers to honor their agreement. Barbara and Johannes were married on 27 April 1597.<ref>Caspar, ''Kepler''. pp.&nbsp;71–75.</ref>

In the first years of their marriage, the Keplers had two children (Heinrich and Susanna), both of whom died in infancy. In 1602, they had a daughter (Susanna); in 1604, a son (Friedrich); and in 1607, another son (Ludwig).<ref>Connor. ''Kepler's Witch'', pp.&nbsp;89–100, 114–116; Caspar. ''Kepler'', pp.&nbsp;75–77</ref>

==== Other research ====
Following the publication of ''Mysterium'' and with the blessing of the Graz school inspectors, Kepler began an ambitious program to extend and elaborate his work. He planned four additional books: one on the stationary aspects of the universe (the Sun and the fixed stars); one on the planets and their motions; one on the physical nature of planets and the formation of geographical features (focused especially on Earth); and one on the effects of the heavens on the Earth, to include atmospheric optics, meteorology, and astrology.<ref>Caspar. ''Kepler'', pp.&nbsp;85–86.</ref>

He also sought the opinions of many of the astronomers to whom he had sent ''Mysterium'', among them [[Reimarus Ursus]] (Nicolaus Reimers Bär)—the imperial mathematician to [[Rudolf II, Holy Roman Emperor|Rudolf II]] and a bitter rival of [[Tycho Brahe]]. Ursus did not reply directly, but republished Kepler's flattering letter to pursue his priority dispute over (what is now called) the [[Tychonic system]] with Tycho. Despite this black mark, Tycho also began corresponding with Kepler, starting with a harsh but legitimate critique of Kepler's system; among a host of objections, Tycho took issue with the use of inaccurate numerical data taken from Copernicus. Through their letters, Tycho and Kepler discussed a broad range of astronomical problems, dwelling on lunar phenomena and Copernican theory (particularly its theological viability). But without the significantly more accurate data of Tycho's observatory, Kepler had no way to address many of these issues.<ref>Caspar, ''Kepler'', pp.&nbsp;86–89</ref>

Instead, he turned his attention to [[chronology]] and "harmony", the [[numerology|numerological]] relationships among music, [[mathematics]] and the physical world, and their [[astrology|astrological]] consequences. By assuming the Earth to possess a soul (a property he would later invoke to explain how the Sun causes the motion of planets), he established a speculative system connecting [[astrological aspects]] and astronomical distances to [[meteorology|weather]] and other earthly phenomena. By 1599, however, he again felt his work limited by the inaccuracy of available data—just as growing religious tension was also threatening his continued employment in Graz. 

====Expulsion from Graz====
Graz was a largely Protestant, mostly Lutheran, city, while the ruler of Inner Austria was a Catholic [[House of Habsburg|Habsburg]]. In 1578, [[Charles II, Archduke of Austria|Duke Charles II]] had granted considerable privileges to Protestants in the [[Pacification of Bruck]]. Charles died in 1590, when his son and heir [[Ferdinand II, Holy Roman Emperor|Ferdinand II]] was 12 years old. Ferdinand was educated in the Jesuit College and [[University of Ingolstadt]], and became full ruler of Inner Austria in 1596. He travelled to Italy in 1598, and returned with a determination to restore the true Catholic faith and eliminate heresy. Kepler wrote to a friend in June of that year expressing his foreboding for the future.<ref>{{cite book | last1=Franzl | first1=Johann | title=Ferdinand II. [i.e. der Zweite]: Kaiser im Zwiespalt d. Zeit | publisher=Verlag Styria | date=1978 | isbn=978-3-222-11119-8 | language=de | page=57}}</ref> As Ferdinand's biographer [[Robert L. Bireley|Robert L. Bireley]] wrote, his fears were justified, as the [[Counter-Reformation]] gained strength.<ref name=Bireley>{{cite book | last1=Bireley | first1=Robert | title=Ferdinand II, Counter-Reformation Emperor, 1578-1637 | publisher=Cambridge University Press | publication-place=Cambridge | date=2014 | isbn=978-1-107-06715-8 | pages=25–31}}</ref>

 [[File:Tycho Brahe.JPG|thumb|upright=.9|[[Tycho Brahe]]]]
In September 1598, Ferdinand ordered all Protestant preachers and teachers to leave the country. Kepler was exempted from the decree, but did not feel secure, and looked for alternatives. He learned that Tycho  Brahe had been appointed Imperial Mathematician in Prague, and Kepler re-established contact. In December 1599, Tycho invited Kepler to visit him in [[Prague]]; on 1 January 1600 (before he even received the invitation), Kepler set off in the hopes that Tycho's patronage could solve his philosophical problems as well as his social and financial ones.<ref>Caspar, ''Kepler'', pp.&nbsp;89–100</ref> On 4 February 1600, Kepler met [[Tycho Brahe]] and his assistants [[Franz Tengnagel]] and [[Longomontanus]] at [[Benátky nad Jizerou]] (35&nbsp;km from Prague), the site where Tycho's new observatory was being constructed. Over the next two months, he stayed as a guest, analyzing some of Tycho's observations of Mars; Tycho guarded his data closely, but was impressed by Kepler's theoretical ideas and soon allowed him more access. Kepler planned to test his theory from ''Mysterium Cosmographicum'' based on the Mars data, but he estimated that the work would take up to two years (since he was not allowed to simply copy the data for his own use). With the help of [[Johannes Jessenius]], Kepler attempted to negotiate a more formal employment arrangement with Tycho, but negotiations broke down in an angry argument and Kepler left for Prague on 6 April. Kepler and Tycho soon reconciled and eventually reached an agreement on salary and living arrangements, and in June, Kepler returned home to Graz to collect his family.<ref>Caspar, ''Kepler'', pp.&nbsp;100–108.</ref>

The situation in Graz made it impossible to return immediately to Brahe; in hopes of continuing his astronomical studies, Kepler sought an appointment as a mathematician to Duke Ferdinand. To that end, Kepler composed an essay—dedicated to Ferdinand—in which he proposed a force-based theory of lunar motion: "In Terra inest virtus, quae Lunam ciet" ("There is a force in the earth which causes the moon to move").<ref>Caspar, ''Kepler'', p. 110.</ref> Though the essay did not earn him a place in Ferdinand's court, it did detail a new method for measuring lunar eclipses, which he applied during the 10 July eclipse in Graz. These observations formed the basis of his explorations of the laws of optics that would culminate in ''Astronomiae Pars Optica''.<ref>Caspar, ''Kepler'', pp.&nbsp;108–111.</ref> Then on 17 July a new decree was announced, ordering all inhabitants to renounce the Protestant faith or leave the province. This time there was no exception for Kepler, and he and his wife and step-daughter left Graz for Prague on 30 September 1600.<ref>{{cite book | last1=Burke-Gaffney | first1=Michael Walter | title=Kepler and the Jesuits | publisher=Bruce publishing Company | date=1944 | url=https://archive.org/details/keplerjesuits00burk| access-date=15 September 2025 | page=}}</ref><ref>{{cite book | last1=Osterhage | first1=Wolfgang | title=Johannes Kepler | publisher=Springer | date=2020 | isbn=978-3-030-46857-6 | pages=48–49}}</ref><ref>{{cite book | last1=Methuen | first1=Charlotte | chapter=Kepler, Religion and Natural Philosophy: A Theological Biography |editor1-last=Davis | editor1-first=A.E.L. |editor2-last=Field | editor2-first=J.V. | editor3-last=Mahoney  | editor3-first=T.J. | title=Reading the Mind of God: Johannes Kepler and the Reform of Astronomy | publisher=Springer Netherlands | publication-place=Dordrecht | date=2024 | isbn=978-94-024-2248-1 | doi=10.1007/978-94-024-2250-4 | pages=1–24}}</ref>

== Scientific career ==
=== Prague (1600–1612) ===
Once established in Prague, he was supported directly by Tycho, who assigned him to analyzing planetary observations and writing a tract against Tycho's (by then deceased) rival, Ursus. In September, Tycho secured him a commission as a collaborator on the new project he had proposed to the emperor: the ''[[Rudolphine Tables]]'' that should replace the ''[[Prutenic Tables]]'' of [[Erasmus Reinhold]]. Two days after Tycho's unexpected death on 24 October 1601, Kepler was appointed his successor as the imperial mathematician with the responsibility to complete his unfinished work. The next 11 years as imperial mathematician would be the most productive of his life.<ref>Caspar, ''Kepler'', pp.&nbsp;111–122.</ref>

=== Imperial Advisor ===
Kepler's primary obligation as imperial mathematician was to provide astrological advice to the emperor, Rudolf II. Though Kepler took a dim view of the attempts of contemporary astrologers to precisely predict the future or divine specific events, he had been casting well-received detailed horoscopes for friends, family, and patrons since his time as a student in Tübingen. In addition to horoscopes for allies and foreign leaders, the emperor sought Kepler's advice in times of political trouble. Rudolf was actively interested in the work of many of his court scholars (including numerous [[Alchemy|alchemists]]) and kept up with Kepler's work in physical astronomy as well.<ref>Caspar, ''Kepler'', pp.&nbsp;149–153</ref>

Officially, the only acceptable religious doctrines in Prague were Catholic and [[Utraquist]], but Kepler's position in the imperial court allowed him to practice his Lutheran faith unhindered. The emperor nominally provided an ample income for his family, but the difficulties of the over-extended imperial treasury meant that actually getting hold of enough money to meet financial obligations was a continual struggle. Partly because of financial troubles, his life at home with Barbara was unpleasant, marred with bickering and bouts of sickness. Court life, however, brought Kepler into contact with other prominent scholars ([[Johannes Matthäus Wackher von Wackhenfels]], [[Jost Bürgi]], [[David Fabricius]], Martin Bachazek, and Johannes Brengger, among others) and astronomical work proceeded rapidly.<ref>Caspar, ''Kepler'', pp.&nbsp;146–148, 159–177</ref>

=== Supernova of 1604 ===
{{See also|Kepler's Supernova}} [[File:Keplers supernova.jpg|thumb|upright=.9|Remnant of Kepler's Supernova [[SN 1604]]]]
In October 1604, a bright new evening star ([[SN 1604]]) appeared, but Kepler did not believe the rumors until he saw it himself.<ref>Caspar, ''Kepler'', p.&nbsp;151.</ref> Kepler began systematically observing the supernova. Astrologically, the end of 1603 marked the beginning of a [[fiery trigon]], the start of the about 800-year cycle of [[great conjunction]]s; astrologers associated the two previous such periods with the rise of [[Charlemagne]] (c. 800 years earlier) and the birth of Christ (c. 1600 years earlier), and thus expected events of great portent, especially regarding the emperor.<ref>Caspar, ''Kepler'', pp.&nbsp;151–153.</ref>

It was in this context, as the imperial mathematician and astrologer to the emperor, that Kepler described the new star two years later in his ''[[De Stella Nova]]''. In it, Kepler addressed the star's astronomical properties while taking a skeptical approach to the many astrological interpretations then circulating. He noted its fading luminosity, speculated about its origin, and used the lack of observed [[Parallax in astronomy|parallax]] to argue that it was beyond the planetary orbits, and thus in the sphere of fixed stars, further undermining the doctrine of the immutability of the heavens (the idea accepted since Aristotle that the [[celestial spheres]] were perfect and unchanging). The birth of a new star implied the variability of the heavens. Kepler also attached an appendix where he discussed the recent chronology work of the Polish historian [[Laurentius Suslyga]]; he calculated that, if Suslyga was correct that accepted timelines were four years behind, then the [[Star of Bethlehem]]—analogous to the present new star—would have coincided with the first great conjunction of the earlier 800-year cycle.<ref>Caspar, ''Kepler'', pp.&nbsp;153–157</ref>

Over the following years, Kepler attempted (unsuccessfully) to begin a collaboration with Italian astronomer [[Giovanni Antonio Magini]], and dealt with chronology, especially the [[Chronology of Jesus|dating of events in the life of Jesus]]. Around 1611, Kepler circulated a manuscript of what would eventually be published (posthumously) as ''[[Somnium (novel)|Somnium]]'' [The Dream]. Part of the purpose of ''Somnium'' was to describe what practicing astronomy would be like from the perspective of another planet, to show the feasibility of a non-geocentric system. The manuscript, which disappeared after changing hands several times, described a fantastic trip to the Moon; it was part allegory, part autobiography, and part treatise on interplanetary travel (and is sometimes described as the first work of science fiction). Years later, a distorted version of the story may have instigated the witchcraft trial against his mother, as the mother of the narrator consults a demon to learn the means of space travel. Following her eventual acquittal, Kepler composed 223 footnotes to the story—several times longer than the actual text—which explained the allegorical aspects as well as the considerable scientific content (particularly regarding lunar geography) hidden within the text.<ref>Lear, ''Kepler's Dream'', pp.&nbsp;1–78</ref>

== Later life ==
=== Troubles ===
[[File:Karlova str No4, Prague Old Town.jpg|thumb|left|upright=0.8|Karlova street in Old Town, [[Prague]]&nbsp;– the house where Kepler lived, now a museum]]
During Kepler's time in Prague, religious and political tensions were building up in the Empire, both between Protestants and Catholics, and within the Habsburg dynasty over the isssue of succession. The situation in Prague, a cosmopolitan city, became increasingly difficult, and Kepler considered a move to Württemberg, which he considered his homeland. In 1609 he wrote to the Duke, [[John Frederick, Duke of Württemberg|Johann Frederick]], requesting a position in the [[University of Tübingen]]. The Duke turned down the request, but sent a present as a token of goodwill. Kepler replied, and in his letter summarised his position on the doctrinal issues that had caused problems in the past. The Duke did not repond to this. Two years later, he tried again, but this time the request was referred to the theological consistory in Stuttgart, who rejected Kepler's request on 25 April 1611, denouncing his [[Calvinist]] leanings both in his reservations about the [[Formula of Concord]], and his insistence that Calvinists should, despite disagreements, be considered "brothers in Christ".<ref>{{cite book | last1=Rothman | first1=Aviva | title=The Pursuit of Harmony: Kepler on Cosmos, Confession, and Community | publisher=University of Chicago Press | date=2017 | isbn=978-0-226-49697-9 | doi=10.7208/chicago/9780226497020.003.0003  | pages=79–82}}</ref><ref>{{cite book | editor1-last=Auweele |  editor1-first=Dennis Vanden | editor2-last=Vassányi | editor2-first=Miklos | last1=Vassányi | first1=Miklos | title=Past and Present Political Theology | chapter= Kepler, the supra-confessional Lutheran | publisher=Routledge | publication-place=Abingdon New York (N.Y.) | date=2020 | isbn=978-0-367-40755-1 | pages=11–34}}</ref><ref>{{cite book |author=Stuttgart Lutheran Consistory to Duke Johann Friedrich of Württemberg | chapter=Advice to refuse Kepler's application for a professorship at the Tübingen Academy on grounds of his Calvinist views on the Holy Communion |editor1-last=Caspar |editor1-first=Max |title=Johannes Kepler Gesammelte Werke Band 16 Briefe 1607 - 1611 |date=1954 |publisher=C. H. Beck'sche Verlagsbuchhandlung |location=München | language=de |pages=464–465, No. 609 Nachbericht |url=https://publikationen.badw.de/de/002334750/002334750.pdf}}</ref>

In 1611, Emperor Rudolf's health was failing, and he was forced to abdicate as [[List of rulers of Bohemia|King of Bohemia]] by his brother [[Matthias, Holy Roman Emperor|Matthias]]. Both sides sought Kepler's astrological advice, an opportunity he used to deliver conciliatory political advice (with little reference to the stars, except in general statements to discourage drastic action). However, it was clear that Kepler's future prospects in the court of Matthias were bleak.<ref>Caspar, ''Kepler'', pp.&nbsp;202–204</ref>

Also in that year, Kepler's wife Barbara contracted [[Hungarian spotted fever]] and began having [[seizure]]s. While she was recovering, all three of their children fell sick with smallpox; six-year-old Friedrich died. As well as his approach to Württemberg, Kepler was in contact with Padua.  The [[University of Padua]] — on the recommendation of the departing Galileo — sought Kepler to fill the mathematics professorship, but Kepler, preferring to keep his family in German territory, instead travelled to Austria to arrange a position as teacher and district mathematician in [[Linz]]. However, Barbara relapsed into illness and died shortly after Kepler's return.<ref>Connor, ''Kepler's Witch'', pp.&nbsp;222–226; Caspar, ''Kepler'', pp.&nbsp;204–207</ref>

Postponing the move to Linz, Kepler remained in Prague until Rudolf's death in early 1612, though political upheaval, religious tension, and family tragedy (along with the legal dispute over his wife's estate) prevented him from doing any research. Instead, he pieced together a chronology manuscript, ''Eclogae Chronicae'', from correspondence and earlier work. Upon his succession as Holy Roman Emperor, Matthias re-affirmed Kepler's position (and salary) as imperial mathematician but allowed him to move to Linz.<ref>Caspar, ''Kepler'', pp.&nbsp;208–211</ref>

=== Linz (1612–1630) ===
[[File:Kepler Statue Linz.jpg|thumb|A statue of Kepler in [[Linz]]]]
In Linz, Kepler's primary responsibilities (beyond completing the ''Rudolphine Tables'') were teaching at the district school and providing astrological and astronomical services. In his first years there, he enjoyed financial security and religious freedom relative to his life in Prague—though he was excluded from [[Eucharist]] by his Lutheran church over his theological scruples. It was during his time in Linz that Kepler had to deal with the accusation and ultimate verdict of witchcraft against his mother [[Katharina Kepler|Katharina]] in the Protestant town of [[Leonberg]]. That blow, happening only a few years after his [[excommunication]], is not seen as a coincidence but as a symptom of the full-fledged assault waged by the Lutherans against Kepler.<ref>{{Cite book|url=https://books.google.com/books?id=GhamrvcsVyIC&q=mazer+waged+an+assault+against+kepler&pg=PT125|title=Shifting the Earth: The Mathematical Quest to Understand the Motion of the Universe|last=Mazer|first=Arthur|publisher=John Wiley & Sons, Inc.|year=2010|isbn=978-1-118-02427-0|location=Hoboken, NJ}}</ref>

His first publication in Linz was ''De vero Anno'' (1613), an expanded treatise on the year of Christ's birth. He also participated in deliberations on whether to introduce [[Pope Gregory XIII|Pope Gregory]]'s [[Gregorian calendar|reformed calendar]] to Protestant German lands. On 30&nbsp;October 1613, Kepler married Susanna Reuttinger. Following the death of his first wife Barbara, Kepler had considered 11 different matches over two years (a decision process formalized later as the [[Secretary problem|marriage problem]]).<ref name="ferguson">{{cite journal |last=Ferguson |first=Thomas S. |author-link= Thomas S. Ferguson |title=Who solved the secretary problem ? |journal=Statistical Science |volume=4 |issue=3 |date=1989 |pages=282–289 |quote=When the celebrated German astronomer, Johannes Kepler (1571–1630), lost his first wife to cholera in 1611, he set about finding a new wife using the same methodical thoroughness and careful consideration of the data that he used in finding the orbit of Mars to be an ellipse&nbsp;... The process consumed much of his attention and energy for nearly 2 years&nbsp;... |jstor=2245639 |doi=10.1214/ss/1177012493 |doi-access=free }}</ref> He eventually returned to Reuttinger (the fifth match) who, he wrote, "won me over with love, humble loyalty, economy of household, diligence, and the love she gave the stepchildren".<ref>Quotation from Connor, ''Kepler's Witch'', p. 252, translated from an 23 October 1613 letter from Kepler to an anonymous nobleman</ref> The first three children of this marriage (Margareta Regina, Katharina, and Sebald) died in childhood. Three more survived into adulthood: Cordula (born 1621); Fridmar (born 1623); and Hildebert (born 1625). According to Kepler's biographers, this was a much happier marriage than his first.<ref>Caspar, ''Kepler'', pp.&nbsp;220–223; Connor, ''Kepler's Witch'', pp.&nbsp;251–254.</ref>

[[File:Regensburg Peterskirchlein Gedenktafel Kepler.jpg|thumb|upright=0.85|Regensburg, church {{lang|de|Peterskirchlein}}, memorial plate for the tomb of Johannes Kepler]]
On 8 October 1630, Kepler set out for Regensburg, hoping to collect interest on work he had done previously. A few days after reaching Regensburg, he became sick and progressively worsened. Kepler died on 15&nbsp;November 1630, just over a month after his arrival. He was buried in a Protestant churchyard in Regensburg, which was completely destroyed during the [[Thirty Years' War]].<ref>Caspar, ''Kepler'', pp.&nbsp;358–360</ref>

=== Christianity ===
Kepler's belief that God created the cosmos in an orderly fashion caused him to attempt to determine and comprehend the laws that govern the natural world, most profoundly in astronomy.<ref>{{Cite web | url=https://www.britannica.com/biography/Johannes-Kepler | title=Johannes Kepler {{pipe}} Biography, Discoveries, & Facts| date=31 August 2023}}</ref><ref>{{Cite web | url=https://www.britannica.com/science/astronomy/The-techniques-of-astronomy#ref1211452 | title=Astronomy – the techniques of astronomy| date=26 July 2024}}</ref> The phrase "I am merely thinking God's thoughts after Him" has been attributed to him, although this is probably a capsulized version of a writing from his hand:
<blockquote>Those laws [of nature] are within the grasp of the human mind; God wanted us to recognize them by creating us after his own image so that we could share in his own thoughts.<ref>Letter (9/10 Apr 1599) to the Bavarian chancellor Herwart von Hohenburg. Collected in Carola Baumgardt and Jamie Callan, ''Johannes Kepler Life and Letters'' (1953), 50</ref></blockquote>Kepler advocated for [[Religious tolerance|tolerance]] among Christian denominations, for example arguing that Catholics and Lutherans should be able to take communion together. He wrote, "Christ the Lord neither was nor is Lutheran, nor Calvinist, nor Papist."<ref>{{Cite journal |last=Rothman |first=Aviva |date=1 January 2020 |title=Johannes Kepler's pursuit of harmony |url=http://physicstoday.scitation.org/doi/10.1063/PT.3.4388 |journal=Physics Today |language=en |volume=73 |issue=1 |pages=36–42 |doi=10.1063/PT.3.4388 |bibcode=2020PhT....73a..36R |s2cid=214144110 |issn=0031-9228|url-access=subscription }}</ref>

== Astronomy ==
=== ''Mysterium Cosmographicum'' ===
[[File:Kepler-solar-system-1.png|thumb|Kepler's [[Platonic solid]] model of the [[Solar System]], from ''[[Mysterium Cosmographicum]]'' (1596)]]

Kepler's first major astronomical work was ''[[Mysterium Cosmographicum]]'' (''The Cosmographic Mystery'', 1596). Kepler claimed to have had an [[epiphany (feeling)|epiphany]] on 19 July 1595, while teaching in [[Graz]], demonstrating the periodic [[Conjunction (astronomy and astrology)|conjunction]] of [[Saturn]] and [[Jupiter]] in the [[zodiac]]: he realized that [[regular polygon]]s bound one inscribed and one circumscribed circle at definite ratios, which, he reasoned, might be the geometrical basis of the universe. After failing to find a unique arrangement of polygons that fit known astronomical observations (even with extra planets added to the system), Kepler began experimenting with 3-dimensional [[polyhedron|polyhedra]]. He found that each of the five [[Platonic solid]]s could be inscribed and circumscribed by spherical [[orb (astronomy)|orbs]]; nesting these solids, each encased in a sphere, within one another would produce six layers, corresponding to the six known planets—[[Mercury (planet)|Mercury]], [[Venus]], [[Earth]], [[Mars]], Jupiter, and Saturn. By ordering the solids selectively—[[octahedron]], [[icosahedron]], [[dodecahedron]], [[tetrahedron]], [[cube]]—Kepler found that the spheres could be placed at intervals corresponding to the relative sizes of each planet's path, assuming the planets circle the Sun. Kepler also found a formula relating the size of each planet's orb to the length of its [[orbital period]]: from inner to outer planets, the ratio of increase in orbital period is twice the difference in orb radius. 

Kepler thought the ''Mysterium'' had revealed God's geometrical plan for the universe. Much of Kepler's enthusiasm for the Copernican system stemmed from his [[theological]] convictions about the connection between the physical and the [[Spirituality|spiritual]]; the universe itself was an image of God, with the Sun corresponding to the Father, the stellar sphere to the [[Jesus|Son]], and the intervening space between them to the [[Holy Spirit in Christianity|Holy Spirit]]. His first manuscript of ''Mysterium'' contained an extensive chapter reconciling heliocentrism with biblical passages that seemed to support geocentrism.<ref>Barker and Goldstein. "Theological Foundations of Kepler's Astronomy," pp.&nbsp;99–103, 112–113.</ref> With the support of his mentor Michael Maestlin, Kepler received permission from the Tübingen university senate to publish his manuscript, pending removal of the Bible [[exegesis]] and the addition of a simpler, more understandable, description of the Copernican system as well as Kepler's new ideas. ''Mysterium'' was published late in 1596, and Kepler received his copies and began sending them to prominent astronomers and patrons early in 1597; it was not widely read, but it established Kepler's reputation as a highly skilled astronomer. The effusive dedication, to powerful patrons as well as to the men who controlled his position in Graz, also provided a crucial doorway into the [[Patronage|patronage system]].<ref>Caspar. ''Kepler'', pp.&nbsp;65–71.</ref>

In 1621, Kepler published an expanded second edition of ''Mysterium'', half as long again as the first, detailing in footnotes the corrections and improvements he had achieved in the 25 years since its first publication.<ref>Field. ''Kepler's Geometrical Cosmology'', Chapter IV, pp. 73ff.</ref> In terms of impact, the ''Mysterium'' can be seen as an important first step in modernizing the theory proposed by [[Nicolaus Copernicus|Copernicus]] in his ''[[De revolutionibus orbium coelestium]]''. While Copernicus sought to advance a heliocentric system in this book, he resorted to [[Ptolemy|Ptolemaic]] devices (viz., epicycles and eccentric circles) in order to explain the change in planets' orbital speed, and also continued to use as a point of reference the center of the Earth's orbit rather than that of the Sun "as an aid to calculation and in order not to confuse the reader by diverging too much from Ptolemy." Modern astronomy owes much to ''Mysterium Cosmographicum'', despite flaws in its main thesis, "since it represents the first step in cleansing the Copernican system of the remnants of the Ptolemaic theory still clinging to it."<ref>Dreyer, J.L.E. ''A History of Astronomy from [[Thales]] to Kepler'', Dover Publications, 1953, pp.&nbsp;331, 377–379.</ref> Kepler never abandoned his five solids theory, publishing the second edition of ''Mysterium'' in 1621 and affirming his continued belief in the validity of the model. Although he noted that there were discrepancies between the observational data and his model's predictions, he did not think they were large enough to invalidate the theory.<ref>{{Cite book |last=Field |first=Judith Veronica |title=Kepler's geometrical cosmology |date=2013 |publisher=Bloomsbury |isbn=978-1-4725-0703-7 |series=Bloomsbury academic collections. Philosophy |location=London |pages=94}}</ref>

=== ''Astronomia Nova'' ===
[[File:Kepler Mars retrograde.jpg|thumb|upright=.9|Diagram of the [[geocentric]] trajectory of Mars through several periods of [[apparent retrograde motion]] in ''Astronomia Nova'' (1609)]]
The extended line of research that culminated in ''[[Astronomia Nova]]'' (''A New Astronomy'')—including the first two [[Kepler's laws of planetary motion|laws of planetary motion]]—began with the analysis, under Tycho's direction, of the orbit of Mars. In this work Kepler introduced the revolutionary concept of planetary orbit, a path of a planet in space resulting from the action of physical causes, distinct from previously held notion of planetary orb (a spherical shell to which planet is attached). As a result of this breakthrough astronomical phenomena came to be seen as being governed by physical laws.<ref>{{Cite journal|last1=Goldstein|first1=Bernard|last2=Hon|first2=Giora|date=2005|title=Kepler's Move from Orbs to Orbits: Documenting a Revolutionary Scientific Concept|url=https://www.researchgate.net/publication/246602496|journal=Perspectives on Science|volume=13|pages=74–111|doi=10.1162/1063614053714126 |s2cid=57559843 }}</ref> Kepler calculated and recalculated various approximations of Mars's orbit using an [[equant]] (the mathematical tool that Copernicus had eliminated with his system), eventually creating a model that generally agreed with Tycho's observations to within two [[arcminute]]s (the average measurement error). But he was not satisfied with the complex and still slightly inaccurate result; at certain points the model differed from the data by up to eight arcminutes. The wide array of traditional mathematical astronomy methods having failed him, Kepler set about trying to fit an [[Oval|ovoid]] orbit to the data.<ref>Caspar, ''Kepler'', pp.&nbsp;123–128</ref>

In Kepler's religious view of the cosmos, the Sun (a symbol of [[God the Father]]) was the source of motive force in the Solar System. As a physical basis, Kepler drew by analogy on [[William Gilbert (physician)|William Gilbert]]'s theory of the magnetic soul of the Earth from ''[[De Magnete]]'' (1600) and on his own work on optics. Kepler supposed that the motive power (or motive ''species'')<ref>On motive species, see Lindberg, "The Genesis of Kepler's Theory of Light," pp.&nbsp;38–40.</ref> radiated by the Sun weakens with distance, causing faster or slower motion as planets move closer or farther from it.<ref>Koyré, ''The Astronomical Revolution'', pp.&nbsp;199–202.</ref> Using a physical model to derive a trajectory was a major breakthrough. Kepler did not simply assume a circular orbit but attempted to come up with it cause, and did this before discovering the area law<ref>Peter Barker and Bernard R. Goldstein, "Distance and Velocity in Kepler's Astronomy", ''Annals of Science,'' 51 (1994): 59–73, at p.&nbsp;60.</ref> Perhaps this assumption entailed a mathematical relationship that would restore astronomical order. Based on measurements of the [[aphelion]] and [[perihelion]] of the Earth and Mars, he created a formula in which a planet's rate of motion is inversely proportional to its distance from the Sun. Verifying this relationship throughout the orbital cycle required very extensive calculation; to simplify this task, by late 1602 Kepler reformulated the proportion in terms of geometry: ''planets sweep out equal areas in equal times''—his second law of planetary motion.<ref>Caspar, ''Kepler'', pp.&nbsp;129–132</ref>

He then set about calculating the entire orbit of Mars, using the geometrical rate law and assuming an egg-shaped [[ovoid]] orbit. After approximately 40 failed attempts, in late 1604 he at last hit upon the idea of an [[ellipse]],<ref>{{cite book |last = Dreyer |first = John Louis Emil |url = https://books.google.com/books?id=OgRAAQAAIAAJ&pg=PA402 |title = History of the Planetary Systems from Thales to Kepler |publisher = Cambridge University Press |year = 1906 |location = Cambridge, England |page = 402 |author-link = John Louis Emil Dreyer }}</ref> which he had previously assumed to be too simple a solution for earlier astronomers to have overlooked.<ref>Caspar, ''Kepler'', p.&nbsp;133</ref> Finding that an elliptical orbit fit the Mars data (the [[Vicarious Hypothesis]]), Kepler immediately concluded that ''all planets move in ellipses, with the Sun at one focus''—his first law of planetary motion. Because he employed no calculating assistants, he did not extend the mathematical analysis beyond Mars. By the end of the year, he completed the manuscript for ''Astronomia nova'', though it would not be published until 1609 due to legal disputes over the use of Tycho's observations, the property of his heirs.<ref>Caspar, ''Kepler'', pp.&nbsp;131–140; Koyré, ''The Astronomical Revolution'', pp.&nbsp;277–279</ref>

=== ''Epitome of Copernican Astronomy'' ===
{{further|Epitome Astronomiae Copernicanae}}

Since completing the ''Astronomia Nova'', Kepler had intended to compose an astronomy textbook that would cover all the fundamentals of [[Heliocentrism|heliocentric astronomy]].<ref>Caspar, ''Kepler'', pp.&nbsp;239–240, 293–300</ref> Kepler spent the next several years working on what would become ''Epitome Astronomiae Copernicanae'' (''Epitome of Copernican Astronomy''). Despite its title, which merely hints at heliocentrism, the ''Epitome'' is less about Copernicus's work and more about Kepler's own astronomical system. The ''Epitome'' contained all three laws of planetary motion and attempted to explain heavenly motions through physical causes.<ref name="Gingerich pp 302">Gingerich, "Kepler, Johannes" from ''Dictionary of Scientific Biography'', pp.&nbsp;302–304</ref> Although it explicitly extended the first two laws of planetary motion (applied to Mars in ''Astronomia nova'') to all the planets as well as the Moon and the [[Galilean moons|Medicean satellites of Jupiter]], it did not explain how elliptical orbits could be derived from observational data.<ref>Wolf, ''A History of Science, Technology and Philosophy'', pp.&nbsp;140–141; Pannekoek, ''A History of Astronomy'', p. 252</ref>

Originally intended as an introduction for the uninitiated, Kepler sought to model his ''Epitome'' after that of his master [[Michael Maestlin]], who published a well-regarded book explaining the basics of [[Geocentrism|geocentric astronomy]] to non-experts.<ref name=":1">{{Cite journal|last=Rothman|first=A.|date=2021|title=Kepler's Epitome of Copernican Astronomy in context|url=https://onlinelibrary.wiley.com/doi/epdf/10.1111/1600-0498.12356|journal=Centaurus|volume=63|pages=171–191|doi=10.1111/1600-0498.12356|issn=0008-8994|s2cid=230613099|url-access=subscription}}</ref> Kepler completed the first of three volumes, consisting of Books I–III, by 1615 in the same question-answer format of Maestlin's and have it printed in 1617.<ref>{{Cite journal|last=Gingerich|first=Owen|date=1990|title=Five Centuries of Astronomical Textbooks and Their Role in Teaching|url=http://adsabs.harvard.edu/abs/1990teas.conf..189G|journal=The Teaching of Astronomy, Proceedings of IAU Colloq. 105, Held in Williamstown, MA, 27–30 July 1988|pages=189|bibcode=1990teas.conf..189G}}</ref> However, the [[Index Librorum Prohibitorum|banning of Copernican books]] by the Catholic Church, as well as the start of the [[Thirty Years' War]], meant that publication of the next two volumes would be delayed. In the interim, and to avoid being subject to the ban, Kepler switched the audience of the ''Epitome'' from beginners to that of expert astronomers and mathematicians, as the arguments became more and more sophisticated and required advanced mathematics to be understood.<ref name=":1" /> The second volume, consisting of Book IV, was published in 1620, followed by the third volume, consisting of Books V–VII, in 1621.

=== ''Rudolphine Tables'' ===
[[File:Rudolphine tables.jpg|thumb|upright=1.2|Two pages from Kepler's ''Rudolphine Tables'' showing eclipses of the Sun and Moon]]
In the years following the completion of ''Astronomia Nova'', most of Kepler's research was focused on preparations for the ''Rudolphine Tables'' and a comprehensive set of [[ephemerides]] (specific predictions of planet and star positions) based on the table, though neither would be completed for many years.<ref>Caspar, ''Kepler''. pp. 178–179.</ref>

Kepler, at last, completed the ''[[Rudolphine Tables]]'' in 1623, which at the time was considered his major work. However, due to the publishing requirements of the emperor and negotiations with Tycho Brahe's heir, it would not be printed until 1627.<ref>Robert J. King, "Johannes Kepler and Australia", ''The Globe,'' no. 90, 2021, pp. 15–24.</ref>

== Astrology ==
[[File:Kepler-Wallenstein-Horoskop.jpg|thumb|upright=0.9|Kepler's horoscope for [[General Wallenstein]]]]
Like [[Ptolemy]], Kepler considered astrology as the counterpart to astronomy, and as being of equal interest and value. However, in the following years, the two subjects drifted apart until astrology was no longer practiced among professional astronomers.<ref name=":0">{{Cite journal|last=Field|first=J. V.|date=1984|title=A Lutheran Astrologer: Johannes Kepler|url=https://www.jstor.org/stable/41133735|journal=Archive for History of Exact Sciences|volume=31|issue=3|pages=189–272|doi=10.1007/BF00327703|jstor=41133735|bibcode=1984AHES...31..189F|s2cid=119811074|issn=0003-9519}}</ref>

[[Sir Oliver Lodge]] observed that Kepler was somewhat disdainful of astrology in his own day, as he was "continually attacking and throwing sarcasm at astrology, but it was the only thing for which people would pay him, and on it after a fashion he lived.<ref>{{cite book|author-link=Oliver Lodge |author=Lodge, O. J. |contribution=Johann Kepler |title=The World of Mathematics, Vol. 1 |year=1956 |editor-link=James R. Newman |editor=Newman, J. R. |publisher=[[Simon and Schuster]] |page=231}}</ref> Nonetheless, Kepler spent a huge amount of time trying to restore astrology on a firmer philosophical footing, composing numerous astrological calendars, more than 800 nativities, and a number of treatises dealing with the subject of astrology proper.<ref>{{Cite journal|last=Boner|first=P. J.|date=2005|title=Soul-Searching with Kepler: An Analysis of Anima in His Astrology|url=https://doi.org/10.1177/002182860503600102|journal=Journal for the History of Astronomy|language=en|volume=36|issue=1|pages=7–20|doi=10.1177/002182860503600102|bibcode=2005JHA....36....7B|s2cid=124764022|url-access=subscription}}</ref>

=== ''De Fundamentis'' ===
In his bid to become imperial astronomer, Kepler wrote ''De Fundamentis'' (1601), whose full title can be translated as "On Giving Astrology Sounder Foundations", as a short foreword to one of his yearly almanacs.<ref>{{Cite journal|last=Simon|first=G.|date=1975|title=Kepler's astrology: The direction of a reform|url=https://www.sciencedirect.com/science/article/abs/pii/0083665675901221|journal=Vistas in Astronomy|language=en|volume=18|issue=1|pages=439–448|doi=10.1016/0083-6656(75)90122-1|bibcode=1975VA.....18..439S|url-access=subscription}}</ref>

In this work, Kepler describes the effects of the Sun, Moon, and the planets in terms of their light and their influences upon humors, concluding with Kepler's view that the Earth possesses a soul with some sense of geometry. Stimulated by the geometric convergence of rays formed around it, the [[Anima mundi|world-soul]] is sentient but not conscious. As a shepherd is pleased by the piping of a flute without understanding the theory of musical harmony, so likewise Earth responds to the angles and aspects made by the heavens but not in a conscious manner. Eclipses are important as omens because the animal faculty of the Earth is violently disturbed by the sudden intermission of light, experiencing something like emotion and persisting in it for some time.<ref name=":0" />

Kepler surmises that the Earth has "cycles of humors" as living animals do, and provides as an example: "the highest tides of the sea are said by sailors to return after nineteen years around the same days of the year". (This may refer to the 18.6-year [[Lunar node#Effect on tides|lunar node precession cycle]].) Kepler advocates searching for such cycles by gathering observations over a period of many years, "and so far this observation has not been made".<ref>{{Cite journal |last1=Brackenridge |first1=J. Bruce |last2=Rossi |first2=Mary Ann |date=1979 |title=Johannes Kepler's on the More Certain Fundamentals of Astrology Prague 1601 |url=https://www.jstor.org/stable/986232 |journal=Proceedings of the American Philosophical Society |volume=123 |issue=2 |pages=85–116 |jstor=986232 |issn=0003-049X}}</ref>

=== ''Tertius Interveniens'' ===
Kepler and [[Helisaeus Roeslin]] engaged in a series of published attacks and counter-attacks on the importance of astrology after the supernova of 1604; around the same time, physician Philip Feselius published a work dismissing astrology altogether (and Roeslin's work in particular).<ref>Caspar, ''Kepler'', pp.&nbsp;178–181</ref>

In response to what Kepler saw as the excesses of astrology, on the one hand, and overzealous rejection of it, on the other, Kepler prepared ''Tertius Interveniens'' (1610). Nominally this work—presented to the common patron of Roeslin and Feselius—was a neutral mediation between the feuding scholars (the titled meaning "Third-party interventions"), but it also set out Kepler's general views on the value of astrology, including some hypothesized mechanisms of interaction between planets and individual souls. While Kepler considered most traditional rules and methods of astrology to be the "evil-smelling dung" in which "an industrious hen" scrapes, there was an "occasional grain-seed, indeed, even a pearl or a gold nugget" to be found by the conscientious scientific astrologer.<ref>Caspar, ''Kepler'', pp.&nbsp;181–185. The full title is ''Tertius Interveniens, das ist Warnung an etliche Theologos, Medicos vnd Philosophos, sonderlich D. Philippum Feselium, dass sie bey billicher Verwerffung der Sternguckerischen Aberglauben nict das Kindt mit dem Badt aussschütten vnd hiermit jhrer Profession vnwissendt zuwider handlen'', translated by [[C. Doris Hellman]] as "''Tertius Interveniens'', that is warning to some theologians, medics and philosophers, especially D. Philip Feselius, that they in cheap condemnation of the star-gazer's superstition do not throw out the child with the bath and hereby unknowingly act contrary to their profession."</ref>

== Music ==
=== ''Harmonice Mundi'' ===
{{Main|Harmonice Mundi}}
[[File:Kepler-1619-pl-3.jpg|thumb|upright=.9|Geometrical harmonies from ''[[Harmonice Mundi]]'' (1619)]]
Kepler was convinced "that the geometrical things have provided the Creator with the model for decorating the whole world".<ref>Quotation from Caspar, ''Kepler'', pp.&nbsp;265–266, translated from ''Harmonice Mundi''</ref> In ''Harmonice Mundi'' (1619), he attempted to explain the proportions of the natural world—particularly the astronomical and astrological aspects—in terms of music.{{NoteTag|The opening of the movie ''[[Mars et Avril]]'' by [[Martin Villeneuve]] is based on German astronomer Johannes Kepler's cosmological model from the 17th century, ''[[Harmonice Mundi]]'', in which the harmony of the universe is determined by the motion of celestial bodies. [[Benoît Charest]] also composed the score according to this theory.}} The central set of "harmonies" was the ''[[musica universalis]]'' or "music of the spheres", which had been studied by [[Pythagoras]], [[Ptolemy]] and others before Kepler; in fact, soon after publishing ''Harmonice Mundi'', Kepler was embroiled in a priority dispute with [[Robert Fludd]], who had recently published his own harmonic theory.<ref>Caspar, ''Kepler'', pp.&nbsp;264–266, 290–293</ref>

Kepler began by exploring regular polygons and [[regular solid]]s, including the figures that would come to be known as [[Kepler-Poinsot polyhedra|Kepler's solids]]. From there, he extended his harmonic analysis to music, meteorology, and astrology; harmony resulted from the tones made by the souls of heavenly bodies—and in the case of astrology, the interaction between those tones and human souls. In the final portion of the work (Book V), Kepler dealt with planetary motions, especially relationships between [[orbital speed|orbital velocity]] and orbital distance from the Sun. Similar relationships had been used by other astronomers, but Kepler—with Tycho's data and his own astronomical theories—treated them much more precisely and attached new physical significance to them.<ref>Caspar, ''Kepler'', pp.&nbsp;266–290</ref>

Among many other harmonies, Kepler articulated what came to be known as the third law of planetary motion. He tried many combinations until he discovered that (approximately) "''The square of the periodic times are to each other as the cubes of the mean distances''." Although he gives the date of this epiphany (8 March 1618), he does not give any details about how he arrived at this conclusion.<ref name="Miller2009">{{Cite book |last=Miller |first=Arthur I. |author-link=Arthur I. Miller |title=Deciphering the cosmic number: the strange friendship of Wolfgang Pauli and Carl Jung |url=https://archive.org/details/isbn_9780393065329 |url-access=registration |access-date=7 March 2011 |date=2009 |publisher=W. W. Norton & Company |isbn=978-0-393-06532-9 |page=[https://archive.org/details/isbn_9780393065329/page/80 80]}}</ref> However, the wider significance for planetary dynamics of this purely kinematical law was not realized until the 1660s. When conjoined with [[Christiaan Huygens]]' newly discovered law of centrifugal force, it enabled [[Isaac Newton]], [[Edmund Halley]], and perhaps [[Christopher Wren]] and [[Robert Hooke]] to demonstrate independently that the presumed gravitational attraction between the Sun and its planets decreased with the square of the distance between them.<ref>Westfall, ''Never at Rest'', pp.&nbsp;143, 152, 402–403; Toulmin and Goodfield, ''The Fabric of the Heavens'', p. 248; De Gandt, 'Force and Geometry in Newton's Principia', chapter 2; Wolf, ''History of Science, Technology and Philosophy'', p. 150; Westfall, ''The Construction of Modern Science'', chapters 7 and 8</ref> This refuted the traditional assumption of scholastic physics that the power of gravitational attraction remained constant with distance whenever it applied between two bodies, such as was assumed by Kepler and also by Galileo in his mistaken universal law that gravitational fall is uniformly accelerated, and also by Galileo's student Borrelli in his 1666 celestial mechanics.<ref>Koyré, ''The Astronomical Revolution'', p.&nbsp;502</ref>

== Optics ==
=== ''Astronomiae Pars Optica'' ===
[[File:Kepler Optica.jpg|thumb|upright=.8|A plate from ''Astronomiae Pars Optica'', illustrating the structure of [[eye]]s of various species]]
As Kepler slowly continued analyzing Tycho's Mars observations—now available to him in their entirety—and began the slow process of tabulating the ''[[Rudolphine Tables]]'', Kepler also picked up the investigation of the laws of optics from his lunar essay of 1600. Both lunar and [[solar eclipse]]s presented unexplained phenomena, such as unexpected shadow sizes, the red color of a total lunar eclipse, and the reportedly unusual light surrounding a total solar eclipse. Related issues of [[atmospheric refraction]] applied to ''all'' astronomical observations. Through most of 1603, Kepler paused his other work to focus on optical theory; the resulting manuscript, presented to the emperor on 1 January 1604, was published as ''Astronomiae Pars Optica'' (The Optical Part of Astronomy). In it, Kepler described the [[inverse-square law]] governing the intensity of light, reflection by flat and curved mirrors, and principles of [[pinhole camera]]s, as well as the astronomical implications of optics such as [[parallax]] and the apparent sizes of heavenly bodies. He also extended his study of optics to the human eye, and is generally considered by neuroscientists to be the first to recognize that images are projected inverted and reversed by the [[Lens (anatomy)|eye's lens]] onto the [[retina]]. The solution to this dilemma was not of particular importance to Kepler as he did not see it as pertaining to optics, although he did suggest that the image was later corrected "in the hollows of the brain" due to the "activity of the Soul."<ref>Finger, "Origins of Neuroscience," p. 74. [[Oxford University Press]], 2001.</ref>

Today, ''Astronomiae Pars Optica'' is generally recognized as the foundation of modern optics (though the [[law of refraction]] is conspicuously absent).<ref>Caspar, ''Kepler'', pp. 142–146</ref> With respect to the beginnings of [[projective geometry]], Kepler introduced the idea of continuous change of a mathematical entity in this work. He argued that if a [[Focus (geometry)|focus]] of a [[conic section]] were allowed to move along the line joining the foci, the geometric form would morph or degenerate, one into another. In this way, an [[ellipse]] becomes a [[parabola]] when a focus moves toward infinity, and when two foci of an ellipse merge into one another, a circle is formed. As the foci of a hyperbola merge into one another, the hyperbola becomes a pair of straight lines. He also assumed that if a straight line is extended to infinity it will meet itself at a single [[point at infinity]], thus having the properties of a large circle.<ref>[[Morris Kline]], ''Mathematical Thought from Ancient to Modern Times'', p. 299. [[Oxford University Press]], 1972.</ref>

=== ''Dioptrice'' ===
In the first months of 1610, [[Galileo Galilei]]—using his powerful new [[telescope]]—discovered four satellites orbiting Jupiter. Upon publishing his account as ''[[Sidereus Nuncius]]'' [Starry Messenger], Galileo sought the opinion of Kepler, in part to bolster the credibility of his observations. Kepler responded enthusiastically with a short published reply, ''Dissertatio cum Nuncio Sidereo'' [Conversation with the Starry Messenger]. He endorsed Galileo's observations and offered a range of speculations about the meaning and implications of Galileo's discoveries and telescopic methods, for astronomy and optics as well as cosmology and astrology. Later that year, Kepler published his own telescopic observations of the moons in ''Narratio de Jovis Satellitibus'', providing further support of Galileo. To Kepler's disappointment, however, Galileo never published his reactions (if any) to ''Astronomia Nova''.<ref>Caspar, ''Kepler'', pp. 192–197</ref>

Kepler also started a theoretical and experimental investigation of telescopic lenses using a telescope borrowed from Duke Ernest of Cologne.<ref>Koestler, ''The Sleepwalkers'' p. 384</ref> The resulting manuscript was completed in September 1610 and published as ''Dioptrice'' in 1611. In it, Kepler set out the theoretical basis of [[double-convex converging lens]]es and [[double-concave diverging lens]]es—and how they are combined to produce a [[Galilean telescope]]—as well as the concepts of [[real image|real]] vs. [[virtual image|virtual]] images, upright vs. inverted images, and the effects of focal length on magnification and reduction. He also described an improved telescope—now known as the ''astronomical'' or ''[[Keplerian telescope]]''—in which two convex lenses can produce higher magnification than Galileo's combination of convex and concave lenses.<ref>Caspar, ''Kepler'', pp.&nbsp;198–202</ref>

== Mathematics and physics ==
[[File:Kepler conjecture 1.jpg|thumb|upright=.9|A diagram illustrating the [[Kepler conjecture]] from ''Strena Seu de Nive Sexangula'' (1611)]]
As a New Year's gift that year (1611), he also composed for his friend and some-time patron, Baron Wackher von Wackhenfels, a short pamphlet entitled ''Strena Seu de Nive Sexangula'' (''A New Year's Gift of Hexagonal Snow''). In this treatise, he published the first description of the hexagonal symmetry of snowflakes and, extending the discussion into a hypothetical [[atomism|atomistic]] physical basis for their symmetry, posed what later became known as the [[Kepler conjecture]], a statement about the most efficient arrangement for packing spheres.<ref>Schneer, "Kepler's New Year's Gift of a Snowflake," pp.&nbsp;531–545</ref><ref>{{Cite book |last1=Kepler |first1=Johannes |editor1-last=Hardie |editor1-first=Colin |editor-link=Colin Hardie |title=De nive sexangula |trans-title=The Six-sided Snowflake |date=1966 |orig-year=1611 |publisher=Clarendon Press |location=Oxford |oclc=974730 }}</ref> This important mathematical problem has practical applications in the understanding of crystalline solids; it was formally solved by [[Thomas Callister Hales|Thomas Hales]] in 2017.<ref>{{Cite journal |last1=Royall |first1=C. Patrick |last2=Charbonneau |first2=Patrick |last3=Dijkstra |first3=Marjolein |last4=Russo |first4=John |last5=Smallenburg |first5=Frank |last6=Speck |first6=Thomas |last7=Valeriani |first7=Chantal |date=12 November 2024 |title=Colloidal hard spheres: Triumphs, challenges, and mysteries |url=https://link.aps.org/doi/10.1103/RevModPhys.96.045003 |journal=Reviews of Modern Physics |language=en |volume=96 |issue=4 |article-number=045003 |doi=10.1103/RevModPhys.96.045003 |issn=0034-6861|arxiv=2305.02452 |bibcode=2024RvMP...96d5003R }}</ref><ref>{{Cite journal |last1=Hales |first1=Thomas |last2=Adams |first2=Mark |last3=Bauer |first3=Gertrud |last4=Dang |first4=Tat Dat |last5=Harrison |first5=John |last6=Hoang |first6=Le Truong |last7=Kaliszyk |first7=Cezary |last8=Magron |first8=Victor |last9=Mclaughlin |first9=Sean |last10=Nguyen |first10=Tat Thang |last11=Nguyen |first11=Quang Truong |last12=Nipkow |first12=Tobias |last13=Obua |first13=Steven |last14=Pleso |first14=Joseph |last15=Rute |first15=Jason |date=January 2017 |title=A Formal Proof of the Kepler Conjecture |url=https://www.cambridge.org/core/journals/forum-of-mathematics-pi/article/formal-proof-of-the-kepler-conjecture/78FBD5E1A3D1BCCB8E0D5B0C463C9FBC |journal=Forum of Mathematics, Pi |language=en |volume=5 |article-number=e2 |doi=10.1017/fmp.2017.1 |issn=2050-5086|hdl=2066/176365 |hdl-access=free }}</ref>

Kepler wrote the influential mathematical treatise ''Nova stereometria doliorum vinariorum'' in 1613, on measuring the volume of containers such as wine barrels, which was published in 1615.<ref>Caspar, ''Kepler'', pp.&nbsp;209–220, 227–240. In 2018 a complete English translation was published: ''Nova stereometria doliorum vinariorum / New solid geometry of wine barrels. Accessit stereometriæ Archimedeæ supplementum / A supplement to the Archimedean solid geometry has been added''. Edited and translated, with an Introduction, by [[Eberhard Knobloch]]. Paris: Les Belles Lettres, 2018. {{ISBN|978-2-251-44832-9}}</ref> Kepler also contributed to the development of infinitesimal methods and numerical analysis, including iterative approximations, infinitesimals, and the early use of logarithms and transcendental equations.<ref>{{Cite journal|last=Belyi|first=Y. A.|date=1975|title=Johannes Kepler and the development of mathematics|url=https://www.sciencedirect.com/science/article/abs/pii/008366567590149X|journal=Vistas in Astronomy|language=en|volume=18|issue=1|pages=643–660|doi=10.1016/0083-6656(75)90149-X|bibcode=1975VA.....18..643B|url-access=subscription}}</ref><ref>{{Cite journal|last=Thorvaldsen|first=S.|date=2010|title=Early Numerical Analysis in Kepler's New Astronomy|url=https://www.cambridge.org/core/journals/science-in-context/article/abs/early-numerical-analysis-in-keplers-new-astronomy/0E28ED84C5D50F003537FCB2C97B31D0|journal=Science in Context|language=en|volume=23|issue=1|pages=39–63|doi=10.1017/S0269889709990238|s2cid=122605799|url-access=subscription}}</ref> Kepler's work on calculating volumes of shapes, and on finding the optimal shape of a wine barrel, were significant steps toward the development of [[calculus]].<ref>{{Cite web |last=Cardil |first=Roberto |date=2020 |title=Kepler: The Volume of a Wine Barrel |url=https://www.maa.org/book/export/html/117621 |access-date=16 July 2022 |website=Mathematical Association of America}}</ref> [[Simpson's rule]], an approximation method used in [[integral calculus]], is known in German as ''Keplersche Fassregel'' (Kepler's barrel rule).<ref name=Albinus/>

== Legacy ==
=== Reception of his astronomy ===
[[Kepler's laws of planetary motion]] were not immediately accepted. Several major figures such as [[Galileo]] and [[René Descartes]] completely ignored Kepler's ''Astronomia nova''. Many astronomers, including Kepler's teacher, Michael Maestlin, objected to Kepler's introduction of physics into his astronomy. Some adopted compromise positions. [[Ismaël Bullialdus]] accepted elliptical orbits but replaced Kepler's area law with uniform motion in respect to the empty focus of the ellipse, while [[Seth Ward (bishop)|Seth Ward]] used an elliptical orbit with motions defined by an equant.<ref>For a detailed study of the reception of Kepler's astronomy see Wilbur Applebaum, [http://adsabs.harvard.edu/abs/1996HisSc..34..451A "Keplerian Astronomy after Kepler: Researches and Problems"], ''History of Science'', 34(1996): 451–504.</ref><ref>Koyré, ''The Astronomical Revolution'', pp.&nbsp;362–364</ref><ref>North, ''History of Astronomy and Cosmology'', pp. 355–360</ref>

Several astronomers tested Kepler's theory, and its various modifications, against astronomical observations. Two transits of Venus and Mercury across the face of the Sun provided sensitive tests of the theory, under circumstances when these planets could not normally be observed. In the case of the transit of Mercury in 1631, Kepler had been extremely uncertain of the parameters for Mercury, and advised observers to look for the transit the day before and after the predicted date. [[Pierre Gassendi]] observed the transit on the date predicted, a confirmation of Kepler's prediction.<ref>{{cite journal |first=Albert |last = van Helden |title = The Importance of the Transit of Mercury of 1631 |journal=Journal for the History of Astronomy |volume=7 |year=1976 |pages=1–10 |bibcode = 1976JHA.....7....1V |doi=10.1177/002182867600700101 |s2cid = 220916972 }}</ref> This was the first observation of a transit of Mercury. However, his attempt to observe the [[transit of Venus]] just one month later was unsuccessful due to inaccuracies in the Rudolphine Tables. Gassendi did not realize that it was not visible from most of Europe, including Paris.<ref>{{cite web |author=HM Nautical Almanac Office |url=http://www.nao.rl.ac.uk/nao/transit/V_1631/ |title=1631 Transit of Venus |date=10 June 2004 |access-date=28 August 2006 |archive-url=https://web.archive.org/web/20061001062918/http://www.nao.rl.ac.uk/nao/transit/V_1631/ |archive-date=1 October 2006 |url-status=dead}}</ref> [[Jeremiah Horrocks]], who observed the [[Transit of Venus, 1639|1639 Venus transit]], had used his own observations to adjust the parameters of the Keplerian model, predicted the transit, and then built apparatus to observe the transit. He remained a firm advocate of the Keplerian model.<ref>Allan Chapman, [http://adsabs.harvard.edu/abs/1990QJRAS..31..333C "Jeremiah Horrocks, the transit of Venus, and the 'New Astronomy' in early 17th-century England"], ''Quarterly Journal of the Royal Astronomical Society,'' 31 (1990): 333–357.</ref><ref>North, ''History of Astronomy and Cosmology'', pp. 348–349</ref><ref>Wilbur Applebaum and Robert Hatch, [http://adsabs.harvard.edu/abs/1983JHA....14..166A "Boulliau, Mercator, and Horrock's ''Venus in sole visa'': Three Unpublished Letters"], ''[[Journal for the History of Astronomy]]'', 14(1983): 166–179</ref>

''Epitome of Copernican Astronomy'' was read by astronomers throughout Europe, and following Kepler's death, it was the main vehicle for spreading Kepler's ideas. In the period 1630–1650, this book was the most widely used astronomy textbook, winning many converts to ellipse-based astronomy.<ref name="Gingerich pp 302" /> However, few adopted his ideas on the physical basis for celestial motions. In the late 17th century, a number of physical astronomy theories drawing from Kepler's work—notably those of [[Giovanni Alfonso Borelli]] and [[Robert Hooke]]—began to incorporate attractive forces (though not the quasi-spiritual motive species postulated by Kepler) and the Cartesian concept of [[Principle of inertia (physics)|inertia]].<ref>Lawrence Nolan (ed.), ''The Cambridge Descartes Lexicon'', Cambridge University Press, 2016, "Inertia."</ref> This culminated in Isaac Newton's ''[[Philosophiae Naturalis Principia Mathematica|Principia Mathematica]]'' (1687), in which Newton derived Kepler's laws of planetary motion from a force-based theory of [[Newton's law of universal gravitation|universal gravitation]],<ref>Kuhn, ''The Copernican Revolution'', pp.&nbsp;238, 246–252</ref> a mathematical challenge later known as "solving the [[Kepler problem]]".<ref name=":02">{{Cite book |last1=Frautschi |first1=Steven C. |title=The Mechanical Universe: Mechanics and Heat |title-link=The Mechanical Universe |last2=Olenick |first2=Richard P. |last3=Apostol |first3=Tom M. |last4=Goodstein |first4=David L. |date=2007 |publisher=Cambridge University Press |isbn=978-0-521-71590-4 |edition=Advanced |location=Cambridge [Cambridgeshire] |pages=451 |oclc=227002144 |author-link=Steven Frautschi |author-link3=Tom M. Apostol |author-link4=David L. Goodstein}}</ref>

=== History of science ===
[[File:Brahe kepler.jpg|thumb|upright=1.3|right|Monument to Tycho Brahe and Kepler in [[Prague]], Czech Republic]]
Beyond his role in the historical development of astronomy and natural philosophy, Kepler has loomed large in the [[philosophy of science|philosophy]] and [[historiography of science]]. Kepler and his laws of motion were central to early histories of astronomy such as [[Jean-Étienne Montucla]]'s 1758 ''Histoire des mathématiques'' and [[Jean-Baptiste Delambre]]'s 1821 ''Histoire de l'astronomie moderne''. These and other histories written from an [[Age of Enlightenment|Enlightenment]] perspective treated Kepler's metaphysical and religious arguments with skepticism and disapproval, but later [[Romanticism in science|Romantic]]-era natural philosophers viewed these elements as central to his success.
[[William Whewell]], in his influential ''History of the Inductive Sciences'' of 1837, found Kepler to be the archetype of the inductive scientific genius; in his ''Philosophy of the Inductive Sciences'' of 1840, Whewell held Kepler up as the embodiment of the most advanced forms of [[scientific method]]. Similarly, [[Ernst Friedrich Apelt]]—the first to extensively study Kepler's manuscripts, after their purchase by [[Catherine the Great]]—identified Kepler as a key to the "[[Scientific Revolution|Revolution of the sciences]]".
Apelt, who saw Kepler's mathematics, aesthetic sensibility, physical ideas, and theology as part of a unified system of thought, produced the first extended analysis of Kepler's life and work.<ref>Jardine, "Koyré's Kepler/Kepler's Koyré," pp.&nbsp;363–367</ref>

[[Alexandre Koyré]]'s work on Kepler was, after Apelt, the first major milestone in historical interpretations of Kepler's cosmology and its influence. In the 1930s and 1940s, Koyré, and a number of others in the first generation of professional historians of science, described the "[[Scientific Revolution]]" as the central event in the history of science, and Kepler as a (perhaps the) central figure in the revolution. Koyré placed Kepler's theorization, rather than his empirical work, at the center of the intellectual transformation from ancient to modern worldviews. Since the 1960s, the volume of historical Kepler scholarship has expanded greatly, including studies of his astrology and meteorology, his geometrical methods, the role of his religious views in his work, his literary and rhetorical methods, his interaction with the broader cultural and philosophical currents of his time, and even his role as an historian of science.<ref>Jardine, "Koyré's Kepler/Kepler's Koyré," pp.&nbsp;367–372; Shapin, ''The Scientific Revolution'', pp.&nbsp;1–2</ref>

Philosophers of science—such as [[Charles Sanders Peirce]], [[Norwood Russell Hanson]], [[Stephen Toulmin]], and [[Karl Popper]]—have repeatedly turned to Kepler: examples of [[Commensurability (philosophy of science)|incommensurability]], [[analogical reasoning]], falsification, and many other philosophical concepts have been found in Kepler's work. Physicist [[Wolfgang Pauli]] even used Kepler's priority dispute with Robert Fludd to explore the implications of [[analytical psychology]] on scientific investigation.<ref>Pauli, "The Influence of Archetypical Ideas"</ref>

=== Editions and translations ===
Modern translations of a number of Kepler's books appeared in the late-nineteenth and early-twentieth centuries, the systematic publication of his collected works began in 1937 (and is nearing completion in the early 21st century).

An edition in eight volumes, '' Kepleri Opera omnia,'' was prepared by Christian Frisch (1807–1881), during 1858 to 1871, on the occasion of Kepler's 300th birthday.
Frisch's edition only included Kepler's Latin, with a Latin commentary.

A new edition was planned beginning in 1914 by [[Walther von Dyck]] (1856–1934). Dyck compiled copies of Kepler's unedited manuscripts, using international diplomatic contacts to convince the Soviet authorities to lend him the manuscripts kept in Leningrad for photographic reproduction. These manuscripts contained several works by Kepler that had not been available to Frisch. Dyck's photographs remain the basis for the modern editions of Kepler's unpublished manuscripts.

Max Caspar (1880–1956) published his German translation of Kepler's ''Mysterium Cosmographicum'' in 1923. Both Dyck and Caspar were influenced in their interest in Kepler by mathematician [[Alexander von Brill]] (1842–1935). Caspar became Dyck's collaborator, succeeding him as project leader in 1934, establishing the ''Kepler-Kommission'' in the following year. Assisted by Martha List (1908–1992) and Franz Hammer (1898–1969), Caspar continued editorial work during World War II. Max Caspar also published a biography of Kepler in 1948.<ref>Gingerich, introduction to Caspar's ''Kepler'', pp.&nbsp;3–4</ref> The commission was later chaired by Volker Bialas (during 1976–2003) and [[Ulrich Grigull]] (during 1984–1999) and [[Roland Bulirsch]] (1998–2014).<ref>[[Ulrich Grigull]], "Sechzig Jahre Kepler-Kommission", in: Sitzungsberichte der Bayerischen Akademie der Wissenschaften [Sitzung vom 5. Juli 1996], 1996.</ref><ref>[http://www.kepler-kommission.de/ kepler-kommission.de].
Ulf Hashagen, Walther von Dyck (1856–1934). Mathematik, Technik und Wissenschaftsorganisation an der TH München, Stuttgart, 2003.</ref>

=== Cultural influence and eponymy ===
{{Main|List of things named after Johannes Kepler}}
[[File:Kepler-62f with 62e as Morning Star.jpg|thumb|An artist's rendition of [[Kepler-62f]], a potentially habitable [[exoplanet]] discovered using data transmitted by the [[Kepler space telescope]]]]
Kepler has acquired a popular image as an icon of scientific modernity and a man before his time; science popularizer [[Carl Sagan]] described him as "the first [[astrophysicist]] and the last scientific astrologer".<ref>Quote from [[Carl Sagan]], ''[[Cosmos: A Personal Voyage]]'', episode III: "The Harmony of the Worlds".</ref> The debate over Kepler's place in the Scientific Revolution has produced a wide variety of philosophical and popular treatments. One of the most influential is [[Arthur Koestler]]'s 1959 book, ''[[The Sleepwalkers: A History of Man's Changing Vision of the Universe]]'', in which Kepler is unambiguously the hero (morally and theologically, as well as intellectually) of the revolution.<ref>Stephen Toulmin, Review of ''The Sleepwalkers'' in ''The Journal of Philosophy'', Vol. 59, no. 18 (1962), pp.&nbsp;500–503</ref>

A well-received historical novel by [[John Banville]], ''Kepler'' (1981), explored many of the themes developed in Koestler's non-fiction narrative and in the philosophy of science.<ref>William Donahue, "A Novelist's Kepler," ''Journal for the History of Astronomy'', Vol. 13 (1982), pp.&nbsp;135–136; "Dancing the grave dance: Science, art and religion in John Banville's ''Kepler''," ''English Studies'', Vol. 86, no. 5 (October 2005), pp.&nbsp;424–438</ref> A 2004 nonfiction book, ''Heavenly Intrigue'', speculated that Kepler murdered Tycho Brahe to gain access to his data.<ref>[[Marcelo Gleiser]], "Kepler in the Dock", review of Gilder and Gilder's ''Heavenly Intrigue'', ''Journal for the History of Astronomy'', Vol. 35, pt. 4 (2004), pp.&nbsp;487–489</ref>  In 2010 Tycho Brahe was exhumed by a Dutch-Czech team and his bones, teeth and beard where analyzed for mercury. The results conclusively eliminate mercury poisoning as a cause of Brahe's death.<ref>{{cite web | author= | title=Mercury poisoning ruled out as cause of Danish astronomer Tycho Brahe's death | url=https://phys.org/news/2012-11-mercury-poisoning-tycho-brahe-death.html | work=Phys.org | date=15 November 2012 | access-date=20 October 2025}}</ref><ref>{{Cite journal |last1=Rasmussen |first1=K. L. |last2=Kučera |first2=J. |last3=Skytte |first3=L. |last4=Kameník |first4=J. |last5=Havránek |first5=V. |last6=Smolík |first6=J. |last7=Velemínský |first7=P. |last8=Lynnerup |first8=N. |last9=Bruzek |first9=J. |last10=Vellev |first10=J. |date=December 2013 |title=Was He Murdered Or Was He Not?—Part I: Analyses of Mercury in the Remains of T ycho B rahe |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1475-4754.2012.00729.x |journal=Archaeometry |language=en |volume=55 |issue=6 |pages=1187–1195 |doi=10.1111/j.1475-4754.2012.00729.x |bibcode=2013Archa..55.1187R |issn=0003-813X|url-access=subscription }}</ref>

In Austria, a silver collector's [[Euro gold and silver commemorative coins (Austria)#2002 coinage|10-euro Johannes Kepler silver coin]] was minted in 2002. The reverse side of the coin has a portrait of Kepler, who spent some time teaching in Graz and the surrounding areas. Kepler was acquainted with Prince [[Hans Ulrich von Eggenberg]] personally, and he probably influenced the construction of [[Eggenberg Castle]] (the motif of the obverse of the coin). In front of him on the coin is the model of nested spheres and polyhedra from ''Mysterium Cosmographicum''.<ref name="Eggenberg Palace coin">{{cite web | url=http://austrian-mint.at/silbermuenzen?l=en&muenzeSubTypeId=108&muenzeId=336 | title=Eggenberg Palace coin | publisher=Austrian Mint | access-date=9 September 2009 | url-status=dead | archive-url=https://web.archive.org/web/20110531210659/http://www.austrian-mint.at/silbermuenzen?l=en | archive-date=31 May 2011 | df=mdy-all }}</ref>

The German composer [[Paul Hindemith]] wrote an opera about Kepler titled ''[[Die Harmonie der Welt]]'' (1957), and during the prolonged process of its creation he concurrently wrote a symphony of the same name based on the musical ideas he had developed for the opera.<ref>{{Cite journal |last=MacDonald |first=Calum |date=2004 |title=Review of Hindemith: Die Harmonie der Welt |url=https://www.jstor.org/stable/3878689 |journal=Tempo |volume=58 |issue=227 |pages=63–66 |doi=10.1017/S0040298204210063 |jstor=3878689 |issn=0040-2982}}</ref> Hindemith's work inspired [[John Rodgers (geologist)|John Rodgers]] and [[Willie Ruff]] of [[Yale University]] to create a [[synthesizer]] composition based on Kepler's scheme for representing planetary motion with music.<ref>{{Cite journal |last1=Rodgers |first1=John |last2=Ruff |first2=Willie |date=1979 |title=Kepler's Harmony of the World: A Realization for the Ear |url=https://www.jstor.org/stable/27849220 |journal=American Scientist |volume=67 |issue=3 |pages=286–292 |jstor=27849220 |bibcode=1979AmSci..67..286R |issn=0003-0996}}</ref> [[Philip Glass]] wrote an opera called ''[[Kepler (opera)|Kepler]]'' (2009) based on Kepler's life, with a libretto in German and Latin by Martina Winkel.<ref>{{Cite journal |last1=Pasachoff |first1=Jay M. |last2=Pasachoff |first2=Naomi |date=December 2009 |title=Third physics opera for Philip Glass |journal=Nature |language=en |volume=462 |issue=7274 |pages=724 |doi=10.1038/462724a |bibcode=2009Natur.462..724P |s2cid=4391370 |issn=0028-0836|doi-access=free }}</ref>

Directly named for Kepler's contribution to science are: [[Kepler's laws of planetary motion]]; [[Kepler's Supernova]] SN 1604, which he observed and described; the [[Kepler–Poinsot polyhedra]] (a set of geometrical constructions), two of which were described by him; and the [[Kepler conjecture]] on [[sphere packing]]. Places and entities [[List of things named after Johannes Kepler|named in his honor]] include multiple city streets and squares, several educational institutions, [[1134 Kepler|an asteroid]], a [[Kepler (lunar crater)|lunar crater]], and a [[Kepler (Martian crater)|Martian crater]].

The [[Kepler space telescope]] has observed 530,506 stars and detected [[List of exoplanets discovered by the Kepler space telescope|2,778 confirmed planets]] ({{As of|2023|06|16|lc=y}}), many of them named after the telescope and Kepler himself.<ref>{{Cite web |title=Exoplanet and Candidate Statistics |url=https://exoplanetarchive.ipac.caltech.edu/docs/counts_detail.html |access-date=16 June 2023 |website=exoplanetarchive.ipac.caltech.edu}}</ref><ref name="NYT-20181031">{{Cite web |author=Dennis Overbye |url=https://www.nytimes.com/2018/10/30/science/nasa-kepler-exoplanet.html |title=Kepler, the Little NASA Spacecraft That Could, No Longer Can |website=[[Nytimes.com]]|date=30 October 2018 |access-date=31 October 2018}}</ref>

== Works ==
* ''[[Mysterium Cosmographicum]]'' (''The Sacred Mystery of the Cosmos'') (1596)
* ''De Fundamentis Astrologiae Certioribus'' (''[http://www.johannes.cz/kepler.php On Firmer Fundaments of Astrology]'') (1601)
* {{Cite book|title=Astronomiae pars optica|volume=|publisher=Claude de Marne|location=Frankfurt am Main|year=1604|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=158093}}
* ''[[De Stella Nova|De Stella nova in pede Serpentarii]]'' (''On the New Star in Ophiuchus's Foot'') (1606)
* ''[[Astronomia nova]]'' (''New Astronomy'') (1609)
* ''Tertius Interveniens'' (''Third-party Interventions'') (1610)
* ''Dissertatio cum Nuncio Sidereo'' (''Conversation with the Starry Messenger'') (1610)
* ''[https://books.radbouduniversitypress.nl/index.php/rup/catalog/book/dioptrice Dioptrice]'' (1611)
* [https://archive.org/details/jbc.bj.uj.edu.pl.NDIGSTDR042372/ ''De nive sexangula''] (''[https://archive.org/details/sixcorneredsnowf0000joha/ On the Six-Cornered Snowflake]'') (1611)
* ''De vero Anno, quo aeternus Dei Filius humanam naturam in Utero benedictae Virginis Mariae assumpsit'' (1614)<ref>"...&nbsp;in 1614, Johannes Kepler published his book ''De vero anno quo aeternus dei filius humanum naturam in utero benedictae Virginis Mariae assumpsit'', on the chronology related to the Star of Bethlehem.", [http://www.rug.nl/research/kapteyn/bethlehem2014 The Star of Bethlehem], [[Kapteyn Astronomical Institute]]</ref>
* ''Eclogae Chronicae'' (1615, published with ''Dissertatio cum Nuncio Sidereo'')
* ''Nova stereometria doliorum vinariorum'' (''New Stereometry of Wine Barrels'') (1615)
* [https://www.loc.gov/item/45027112/ ''Ephemerides nouae motuum coelestium''] (1617–30)
* {{Cite book|title=Epitome astronomiae copernicanae|volume=|publisher=Johann Planck|location=Linz|year=1618|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=9586372}}
* {{Cite book|title=Epitome astronomiae Copernicanae. 1–3, De doctrina sphaerica|volume=44199|publisher=Johann Planck|location=Linz|year=1618|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=204698}}
** {{Cite book|title=Epitome astronomiae Copernicanae. 4, Doctrina theorica. 1, Physica coelestis|volume=4|publisher=Gottfried Tambach|location=Linz|year=1622|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=205577}}
** {{Cite book|title=Epitome astronomiae Copernicanae. 5–7, Doctrina theorica|volume=44323|publisher=Gottfried Tambach|location=Linz|year=1621|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=205998}}
* {{Cite book|title=De cometis|volume=|publisher=Sebastian Müller|location=Augsburg|year=1619|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=208511}}
* ''[[Harmonice Mundi]]'' (''[https://books.google.com/books?id=rEkLAAAAIAAJ Harmony of the Worlds]'') (1619)
* ''[[Mysterium cosmographicum]]'' (''The Sacred Mystery of the Cosmos''), 2nd edition (1621)
* ''[[Rudolphine Tables|Tabulae Rudolphinae]]'' (''Rudolphine Tables'') (1627)
* ''[[Somnium (novel)|Somnium]]'' ([https://www.loc.gov/item/39010144 ''The Dream'']) (1634) ([https://books.google.com/books?id=OdCJAS0eQ64C English translation on Google Books preview])
* {{Cite book|title=[Opere]|volume=1|publisher=Heyder & Zimmer|location=Frankfurt am Main|year=1858|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=12128068}}
** {{Cite book|title=[Opere]|volume=2|publisher=Heyder & Zimmer|location=Frankfurt am Main|year=1859|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=12130159}}
** {{Cite book|title=[Opere]|volume=3|publisher=Heyder & Zimmer|location=Frankfurt am Main|year=1860|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=12132742}}
** {{Cite book|title=[Opere]|volume=4|publisher=Heyder & Zimmer|location=Frankfurt am Main|year=1863|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=12135025}}
** {{Cite book|title=[Opere]|volume=5|publisher=Heyder & Zimmer|location=Frankfurt am Main|year=1864|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=12137068}}
** {{Cite book|title=[Opere]|volume=6|publisher=Heyder & Zimmer|location=Frankfurt am Main|year=1866|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=12139075}}
** {{Cite book|title=[Opere]|volume=7|publisher=Heyder & Zimmer|location=Frankfurt am Main|year=1868|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=12141460}}
** {{Cite book|title=[Opere]|volume=8|publisher=Heyder & Zimmer|location=Frankfurt am Main|year=1870|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=12144061}}
** {{Cite book|title=[Opere]|volume=9|publisher=Heyder & Zimmer|location=Frankfurt am Main|year=1871|language=la|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=12145780}}

A critical edition of Kepler's collected works (''Johannes Kepler Gesammelte Werke'', KGW) in 22 volumes is being edited by the ''Kepler-Kommission'' (founded 1935) on behalf of the [[Bayerische Akademie der Wissenschaften]].

:Vol. 1: ''Mysterium Cosmographicum. De Stella Nova''. Ed. M. Caspar. 1938, 2nd ed. 1993. Paperback {{isbn|3-406-01639-1}}.
:Vol. 2: ''Astronomiae pars optica''. Ed. F. Hammer. 1939, Paperback {{isbn|3-406-01641-3}}.
:Vol. 3: ''Astronomia Nova''. Ed. M. Caspar. 1937. IV, 487 p. 2. ed. 1990. Paperback {{isbn|3-406-01643-X}}. Semi-parchment {{isbn|3-406-01642-1}}.
:Vol. 4: ''Kleinere Schriften 1602–1611. Dioptrice''. Ed. M. Caspar, F. Hammer. 1941. {{isbn|3-406-01644-8}}.
:Vol. 5: ''Chronologische Schriften''. Ed. F. Hammer. 1953. Out-of-print.
:Vol. 6: ''Harmonice Mundi''. Ed. M. Caspar. 1940, 2nd ed. 1981, {{isbn|3-406-01648-0}}.
:Vol. 7: ''Epitome Astronomiae Copernicanae''. Ed. M. Caspar. 1953, 2nd ed. 1991. {{isbn|3-406-01650-2}}, Paperback {{isbn|3-406-01651-0}}.
:Vol. 8: ''Mysterium Cosmographicum. Editio altera cum notis. De Cometis. Hyperaspistes''. Commentary F. Hammer. 1955. Paperback {{isbn|3-406-01653-7}}.
:Vol 9: ''Mathematische Schriften''. Ed. F. Hammer. 1955, 2nd ed. 1999. Out-of-print.
:Vol. 10: ''Tabulae Rudolphinae''. Ed. F. Hammer. 1969. {{isbn|3-406-01656-1}}.
:Vol. 11,1: ''Ephemerides novae motuum coelestium''. Commentary V. Bialas. 1983. {{isbn|3-406-01658-8}}, Paperback {{isbn|3-406-01659-6}}.
:Vol. 11,2: ''Calendaria et Prognostica. Astronomica minora. Somnium''. Commentary V. Bialas, H. Grössing. 1993. {{isbn|3-406-37510-3}}, Paperback {{isbn|3-406-37511-1}}.
:Vol. 12: ''Theologica. Hexenprozeß. Tacitus-Übersetzung. Gedichte''. Commentary J. Hübner, H. Grössing, F. Boockmann, F. Seck. Directed by V. Bialas. 1990. {{isbn|3-406-01660-X}}, Paperback {{isbn|3-406-01661-8}}.
* Vols. 13–18: Letters:
::Vol. 13: ''Briefe 1590–1599''. Ed. M. Caspar. 1945. 432 p. {{isbn|3-406-01663-4}}.
::Vol. 14: ''Briefe 1599–1603''. Ed. M. Caspar. 1949. Out-of-print. 2nd ed. in preparation.
::Vol 15: ''Briefe 1604–1607''. Ed. M. Caspar. 1951. 2nd ed. 1995. {{isbn|3-406-01667-7}}.
::Vol. 16: ''Briefe 1607–1611''. Ed. M. Caspar. 1954. {{isbn|3-406-01668-5}}.
::Vol. 17: ''Briefe 1612–1620''. Ed. M. Caspar. 1955. {{isbn|3-406-01671-5}}.
::Vol. 18: ''Briefe 1620–1630''. Ed. M. Caspar. 1959. {{isbn|3-406-01672-3}}.
:Vol. 19: ''Dokumente zu Leben und Werk''. Commentary M. List. 1975. {{isbn|978-3-406-01674-5}}.
:Vols. 20–21: manuscripts
::Vol. 20, 1: ''Manuscripta astronomica (I). Apologia, De motu Terrae, Hipparchus etc.'' Commentary V. Bialas. 1988. {{isbn|3-406-31501-1}}. Paperback {{isbn|3-406-31502-X}}.
::Vol. 20, 2: ''Manuscripta astronomica (II). Commentaria in Theoriam Martis''. Commentary V. Bialas. 1998. Paperback {{isbn|3-406-40593-2}}.
::Vol. 21, 1: ''Manuscripta astronomica (III) et mathematica. De Calendario Gregoriano''. In preparation.
::Vol. 21, 2: ''Manuscripta varia''. In preparation.
:Vol. 22: General index, in preparation.

The Kepler-Kommission also publishes ''Bibliographia Kepleriana'' (2nd edition List, 1968), a complete bibliography of editions of Kepler's works, with a supplementary volume to the second edition (ed. Hamel 1998).

== See also ==
{{cols}}
* [[Theoretical physics]]
* [[Cavalieri's principle]]
* [[History of astronomy]]
* [[History of physics]]
** [[Kepler orbit]]
** [[Kepler triangle]]
* [[Kepler–Bouwkamp constant]]
* [[Penrose tiling]]
* [[Radiation pressure]]
{{colend}}

== Notes ==
{{Notelist}}{{NoteFoot}}

== References ==
=== Citations ===
{{Reflist}}

== Sources ==
{{refbegin}}
* Barker, Peter and Bernard R. Goldstein: "Theological Foundations of Kepler's Astronomy". ''Osiris'', Volume 16. ''Science in Theistic Contexts.'' [[University of Chicago Press]], 2001, pp.&nbsp;&nbsp;88–113
* Caspar, Max. ''Kepler''; transl. and ed. by [[C. Doris Hellman]]; with a new introduction and references by Owen Gingerich; bibliographic citations by Owen Gingerich and Alain Segonds. New York: Dover, 1993. {{ISBN|978-0-486-67605-0}}
* Connor, James A. ''Kepler's Witch: An Astronomer's Discovery of Cosmic Order Amid Religious War, Political Intrigue, and the Heresy Trial of His Mother''. HarperSanFrancisco, 2004. {{ISBN|978-0-06-052255-1}}
* De Gandt, Francois. ''Force and Geometry in Newton's'' Principia, Translated by Curtis Wilson, [[Princeton University Press]], 1995. {{ISBN|978-0-691-03367-9}}
* [[J. L. E. Dreyer|Dreyer, J. L. E.]] ''A History of Astronomy from Thales to Kepler''. Dover Publications Inc, 1967. {{isbn|0-486-60079-3}}
* [[Judith V. Field|Field, J. V.]] ''Kepler's geometrical cosmology''. [[University of Chicago Press]], 1988. {{ISBN|978-0-226-24823-3}}
* Gilder, Joshua and Anne-Lee Gilder: ''Heavenly Intrigue: Johannes Kepler, Tycho Brahe, and the Murder Behind One of History's Greatest Scientific Discoveries'', Doubleday (2004). {{ISBN|978-0-385-50844-5}} Reviews [https://web.archive.org/web/20061125003508/http://www.bookpage.com/0407bp/nonfiction/heavenly_intrigue.html bookpage.com], 
* [[Owen Gingerich|Gingerich, Owen]]. ''The Eye of Heaven: Ptolemy, Copernicus, Kepler''. American Institute of Physics, 1993. {{ISBN|978-0-88318-863-7}} (Masters of modern physics; v. 7)
* Gingerich, Owen: "Kepler, Johannes" in ''Dictionary of Scientific Biography'', Volume VII. Charles Coulston Gillispie, editor. New York: Charles Scribner's Sons, 1973
* Jardine, Nick: "Koyré's Kepler/Kepler's Koyré," ''History of Science'', Vol. 38 (2000), pp.&nbsp;&nbsp;363–376
* Kepler, Johannes. ''Johannes Kepler New Astronomy'' trans. W. Donahue, foreword by O. Gingerich, [[Cambridge University Press]] 1993. {{isbn|0-521-30131-9}}
* Kepler, Johannes and Christian Frisch. ''Joannis Kepleri Astronomi Opera Omnia'' (''John Kepler, Astronomer; Complete Works''), 8 volumes (1858–1871). [https://books.google.com/books?id=dTMAAAAAQAAJ&pg=PP9 vol. 1, 1858], [https://books.google.com/books?id=gzMAAAAAQAAJ&pg=PR2 vol. 2, 1859], [https://books.google.com/books?id=qjMAAAAAQAAJ&pg=PP7 vol. 3, 1860], [https://books.google.com/books?id=xjMAAAAAQAAJ&pg=PR6 vol. 6, 1866], [https://books.google.com/books?id=gMkKAAAAIAAJ&dq=kepleri+%22heyder+%26+zimmer%22&pg=PP16 vol. 7, 1868], Frankfurt am Main and Erlangen, Heyder & Zimmer, – [[Google Books]]
* Kepler, Johannes, et al. ''Great Books of the Western World. Volume 16: Ptolemy, Copernicus, Kepler'', Chicago: Encyclopædia Britannica, Inc., 1952. (contains English translations by of Kepler's ''Epitome'', Books IV & V and ''Harmonice'' Book 5)
* [[Arthur Koestler|Koestler, Arthur]]. ''[[The Sleepwalkers (Koestler book)|The Sleepwalkers]]: A History of Man's Changing Vision of the Universe.'' (1959). {{ISBN|978-0-14-019246-9}}
* [[Alexandre Koyré|Koyré, Alexandre]]: ''Galilean Studies'' Harvester Press, 1977. {{ISBN|978-0-85527-354-5}}
* Koyré, Alexandre: ''The Astronomical Revolution: Copernicus-Kepler-Borelli'' Ithaca, NY: [[Cornell University Press]], 1973. {{ISBN|978-0-8014-0504-4}}; Methuen, 1973. {{ISBN|978-0-416-76980-7}}; Hermann, 1973. {{ISBN|978-2-7056-5648-5}}
* [[Thomas Samuel Kuhn|Kuhn, Thomas S.]] ''The Copernican Revolution: Planetary Astronomy in the Development of Western Thought''. Cambridge, MA: Harvard University Press, 1957. {{ISBN|978-0-674-17103-9}}
* Lindberg, David C.: "The Genesis of Kepler's Theory of Light: Light Metaphysics from Plotinus to Kepler." ''Osiris'', N.S. 2. University of Chicago Press, 1986, pp.&nbsp;&nbsp;5–42.
* Lear, John. ''Kepler's Dream''. Berkeley: University of California Press, 1965
* North, John. ''The Fontana History of Astronomy and Cosmology,'' Fontana Press, 1994. {{ISBN|978-0-00-686177-5}}
* Pannekoek, Anton: ''A History of Astronomy'', Dover Publications Inc 1989. {{ISBN|978-0-486-65994-7}}
* [[Wolfgang Pauli|Pauli, Wolfgang]]. ''Wolfgang Pauli&nbsp;– Writings on physics and philosophy'', translated by Robert Schlapp and edited by P. Enz and Karl von Meyenn (Springer Verlag, Berlin, 1994). See section 21, ''The influence of archetypical ideas on the scientific theories of Kepler'', concerning Johannes Kepler and [[Robert Fludd]] (1574–1637). {{ISBN|978-3-540-56859-9}}
* Schneer, Cecil: "Kepler's New Year's Gift of a Snowflake." ''[[Isis (journal)|Isis]]'', Volume 51, No. 4. University of Chicago Press, 1960, pp.&nbsp;&nbsp;531–545.
* Shapin, Steven. ''The Scientific Revolution''. Chicago: University of Chicago Press, 1996. {{ISBN|978-0-226-75020-0}}
* Stephenson, Bruce. ''Kepler's physical astronomy''. New York: Springer, 1987. {{ISBN|978-0-387-96541-3}} (Studies in the history of mathematics and physical sciences; 13); reprinted Princeton:Princeton Univ. Pr., 1994. {{ISBN|978-0-691-03652-6}}
* Stephenson, Bruce. ''The Music of the Heavens: Kepler's Harmonic Astronomy'', [[Princeton University Press]], 1994. {{ISBN|978-0-691-03439-3}}
* Toulmin, Stephen and June Goodfield. ''The Fabric of the Heavens: The Development of Astronomy and Dynamics''. Pelican, 1963.
* [[Richard S. Westfall|Westfall, Richard S.]] ''The Construction of Modern Science: Mechanism and Mechanics''. John Wiley and Sons, 1971. {{isbn|0-471-93531-X}}; reprinted Cambridge University Press, 1978. {{isbn|0-521-29295-6}}
* Westfall, Richard S. ''Never at Rest: A Biography of Isaac Newton''. Cambridge University Press, 1981. {{ISBN|978-0-521-23143-5}}
* Wolf, A. ''A History of Science, Technology and Philosophy in the 16th and 17th centuries''. George Allen & Unwin, 1950.
{{refend}}

== External links ==
{{Sister project links |wikt=no |s=Author:Johannes Kepler |v=no |n=no |b=General Astronomy/Kepler's Laws}}
*[http://digitalcollections.library.cmu.edu/awweb/awarchive?type=file&item=393654 Kepler's Conversation with the Starry Messenger (English translation of ''Dissertation cum Nuncio Sidereo'')] {{Webarchive|url=https://web.archive.org/web/20201017152550/http://digitalcollections.library.cmu.edu/awweb/awarchive?type=file&item=393654 |date=17 October 2020 }}
* [https://kepler.badw.de/kepler-digital.html ''Herausgabe der Werke von Johannes Kepler'' (with links to digital scans of the published volumes)]
* {{MathGenealogy |id = 127098 }}
* {{Gutenberg author |id =43585|name = Johannes Kepler }}
* {{Internet Archive author |sname=Johannes Kepler}}{{Gutenberg|no=12406|name=Kepler|author=Walter W. Bryant}} (1920 book, part of ''Men of Science'' series)
* {{Cite EB1911|wstitle= Kepler, Johann | volume= 15 |last1= Clerke |first1= Agnes Mary |author1-link= Agnes Mary Clerke | pages = 749&ndash;751 |short=1}}
* Plant, David, [https://web.archive.org/web/20120512064724/http://www.skyscript.co.uk/kepler.html Kepler and the "Music of the Spheres"]
* {{MacTutor Biography |id = Kepler |title = Johannes Kepler|mode=cs1}}
*{{YouTube|UJ9SuchDuJc|The Heliocentric Model and Kepler's Laws of Planetary Motion}} - Kepler's three laws of planetary motion in the historic context of developing the Heliocentric model

{{Johannes Kepler}}

{{Portal bar|Biography|Philosophy|History of science|Mathematics|Arithmetic|Astronomy|Music|Physics|Technology|Society|Literature|Speculative fiction|Space|Star|Europe|Germany|Denmark}}

{{Authority control}}

{{DEFAULTSORT:Kepler, Johannes}}
[[Category:Johannes Kepler| ]]
[[Category:1571 births]]
[[Category:1630 deaths]]
[[Category:People from Weil der Stadt]]
[[Category:16th-century German male writers]]
[[Category:16th-century German writers]]
[[Category:17th-century German male writers]]
[[Category:16th-century writers in Latin]]
[[Category:16th-century German mathematicians]]
[[Category:17th-century writers in Latin]]
[[Category:17th-century German mathematicians]]
[[Category:17th-century German novelists]]
[[Category:German expatriates in Austria]]
[[Category:Scientists from Prague]]
[[Category:Austrian Lutherans]]
[[Category:Christian astrologers]]
[[Category:German cosmologists]]
[[Category:German astrologers]]
[[Category:17th-century German astronomers]]
[[Category:German Lutherans]]
[[Category:German music theorists]]
[[Category:Natural philosophers]]
[[Category:Copernican Revolution]]
[[Category:Mathematicians from Prague]]
[[Category:Members of the Lincean Academy]]
[[Category:German writers about music]]
[[Category:Austrian writers about music]]
[[Category:University of Tübingen alumni]]
[[Category:17th-century German philosophers]]
[[Category:16th-century German astronomers]]