A large number of significant but minor figures in the history of science tend to get lost in the shadows of those, whom we have raised to god like status within that history; whole hordes have been swallowed up by the shadows cast by Galileo and Newton. Lesley Murdin even wrote an excellent book, *Under Newton’s Shadow*[1], in acknowledgement of the latter. One figure who suffers from this phenomenon is the German astronomer Michael Mästlin (1550–1631), who if he gets mentioned at all, it is only with reference to his most famous student, Johannes Kepler. Although his substantial influence on Kepler is probably his most important role in the history of astronomy, Mästlin (or Maestlin, as he is usually written in English) deserves to be much better known in his own right.

Michael Mästlin was born 30 September 1550 in Göppingen into a strict Lutheran Protestant family. He was schooled in the convent schools of Königsbronn and Herrenalb. He matriculated at the University of Tübingen in 1658 where he graduated BA in 1569. In the same year he entered the Tübingen Stift (the Lutheran Church hall of residence) with a stipend from the Duke of Württemberg. He graduated MA in in 1571 and completed his theology studies in 1573.

As a student he studied astronomy and mathematics under Philipp Apian (1531–1589) the son of the astronomer, mathematician and cartographer Peter Apian.

Philipp had already succeeded his father as professor for mathematics and astronomy in Ingolstadt at the age of twenty-one. Like many others he studied medicine alongside his teaching duties finishing his medical studies later in the Northern Italian universities. In 1569 he was forced by the Jesuits to quit his post in Ingolstadt because of his membership of the Lutheran Church. In the same year he received the professorship in Tübingen. Apian was professor in Tübingen for fourteen years until he was, ironically, forced to resign because he refused to sign the *Formula of Concord* a document setting out the Lutheran statement of faith and condemning Calvinists.

Apian inspired and guided Mästlin’s interest in astronomy and mathematics. Already in 1570 Mästlin acquired a copy of Copernicus’ *De revolutionibus* and he would go on to become one of the first university teachers to teach Copernican heliocentricity. From 1573 until he first left Tübingen in 1576 he was *Repetens mathematicus* (teacher for revision in the mathematical sciences) at the Stift. In 1570 he published the second edition of Erasmus Reinhold’s *Prutenicae Tabulae*. In 1572 he observed the Supernova, publishing his observations in his *Demonstratio Astronomica Loci Stellae Novae* the following year. In 1575 he represented the absent Apian as mathematics professor.

In 1576 Mästlin was appointed Diaconus (2^{nd} pastor) in the parish of Backnang, a small town near Stuttgart. His clerical appointment didn’t stop his astronomical activities. He observed the comet of 1577 publishing his *Observatio et Demostratio Cometae Aetherei, qui anno … 1577* in 1578. Much is made, in the secondary literature, of Tycho Brahe’s observations of the 1572 supernova and the 1577 comet and how the determination of the supralunar occurrence of both phenomena led to the refutation of the Aristotelian principle of an unchanging heavens. However, at the time Tycho’s were not the only observations and Mästlin’s reports had at least as much if not more influence on the debate as those of Tycho. In fact Tycho named Mästlin as his prime witness confirming his own observations.

In the years between 1578 and 1580 Mästlin constructed his own observing instruments, a quadrant and a Jacob’s staff. In 1580 he published his *Ephemerides Novae … for the years 1577 to 1590*. His highly visible astronomical activities led to Mästlin being appointed professor for astronomy and mathematics at the University of Heidelberg in 1580, which had become Protestant in 1556. In Heidelberg he published the first edition of his astronomy textbook, *Epitome Astronominae*, a standard Ptolemaic geocentric work 1582, which over the years would see six further editions.

In 1584 he was called back to Tübingen his alma mater to succeed his own teacher Philipp Apian as professor for the mathematical sciences, a post that he would hold for more than 47 years until his death in 1631.

Whilst still at Heidelberg Mästlin, as a leading Protestant mathematicus was consulted by the rulers of the German Protestant states on whether to adopt the new Gregorian calendar. In his *Gründtlicher Bericht von der allgemeinen und nunmehr bei 1600 Jahren von dem ersten Kaiser Julio bis jetzt gebrauchten jarrechnung oder kalender* (Rigorous report on the general and up till now for 1600 years used calculation of years or calendar from the first Caesar Julio), published in 1583, he rejected the new calendar on mathematical and astronomical grounds, noting it was not clear how it was calculated, (this information didn’t become available until much later) and also on religious grounds. In his anti-Catholic polemic he referred to the Pope as “seiner Heilosigkeyt”, that is “his Awfulness”, a pun in German on Heiligkeit meaning holiness and Heillos meaning awful. Mästlin played a central role in the rejection of the calendar reform in the Protestant states, who only adopted the Gregorian calendar in 1700.

It is in his role as professor in Tübingen that is best known and in particular his relationship with his most famous student Johannes Kepler. Kepler studied in Tübingen from 1589 till 1594, like Mästlin as a stipendiary in the Tübinger Stift. From Mästlin’s lectures Kepler learnt about the heliocentric system of Copernicus and not through some sort of secret instruction as is often falsely claimed. It was almost certainly Mästlin who recommended Kepler for the post of mathematics teacher in Graz and it was definitely Mästlin who convinced Kepler to accept the post. The two stayed close after Kepler’s move to Graz and exchanged many long letters on a range of subject. In 1596 Mästlin assisted Kepler in getting his *Mysterium Cosmographicum* published, adding Rheticus’ *Narratio Prima, *as an appendix to the work thereby demonstrating his strong support for the Copernican hypothesis.

Strangely after 1600 Mästlin began to distance himself from his most famous pupil, no longer answering all of his letters and declining to help when Kepler was desperately looking for a new position. This cooling of their relationship from the side of the mentor has never been satisfactorily explained but two things probably played a role. On the scientific side Mästlin strongly disapproved of Kepler’s attempts to explain the physical cause of planetary motion, admonishing him to stick to the astronomer’s role of providing mathematical models of that motion and to leave the explanations to the philosophers. Also a thorn in Mästlin’s highly devout Lutheran eyes was Kepler’s sympathy for other religious viewpoints, which led to his being excluded from communion.

Kepler’s was by no means Mästlin’s only renowned student. His most notorious student is certainly Johann Valentin Andreae (1586–1654)

author of the Rosicrucian *Chymische Hochzeit Christiani Rosencreutz anno 1459* (*Chymical Wedding of Christian Rosenkreutz*) published in 1616

and the Christian utopia *Reipublicae Christianopolitanae descriptio* (Description of the Republic of Christianopolis) published in 1619. Andreae initially studied theology and mathematics in Tübingen from 1602 till 1605. Mästlin as his mathematics teacher had a major influence on him also introducing him to Kepler with whom he corresponded until the latters death. He was also responsible for Andeae coming into contact with Kepler’s close friend Christoph Besold, who introduced Andreae to the esoteric studies that would lead to his Rosicrucian activities. Andeae’s utopia is, like that from Bacon, one that is endowed with natural philosophy and the mathematical science.

Less notorious but more scientific than Andeae was the polymath Wilhelm Schickard (1592–1635), who as well as being one of Mästlin’s students was also part of the circle of scholars around Besold and Andeae.

Like Mästlin and Kepler, a student on the Tübinger Stift he graduated MA in 1611 and went on to study theology. 1613 he received the first of various clerical posts. In 1617 he meet and got to know Kepler, in Württemberg for his mother’s witch trial. He provided engravings and woodcuts for Kepler’s magnum opus the *Harmonice Mundi*. In 1619 he was appointed professor for Hebrew in Tübingen and here first displayed his talent for logical analysis and leaning. He invented the *Rota Hebræa* two rotating discs to help his students learn Hebraic conjugations. He also wrote a *Horologium Hebræum* a Hebrew textbook in 24 capitals, each of which was learnable in one hour. During his time as professor for Hebrew he was also an active astronomer amongst other things producing highly accurate ephemerides. Schickard was a skilled instrument maker and in 1623 he designed and built the earliest known calculating machine, his *Rechenuhr* (calculating clock) with the intension of helping Kepler with his astronomical calculations. His calculating machine could only add and subtract but included a set of Napier’s Bones in the form of cylinders to aid multiplication and division. He started to build one for Kepler but it got destroyed in a fire. Knowledge of Schickard’s calculating machine got lost in the seventeenth century but was rediscovered in the twentieth century amongst Kepler’s letters by Max Casper. Bruno von Freytag-Löringhoff reconstructed the machine in the 1960s.

In 1631 Schickard succeeded Mästlin as professor of the mathematical sciences at Tübingen. Like Mästlin, Mästlin’s teacher Apian as well as Kepler, Schickard also worked as a surveyor and cartographer.

Throughout his career as an astronomer Mästlin stood in contact and corresponded with nearly all the leading astronomers in Europe. During his later years as professor Mästlin continued working as an active astronomer. Like Kepler he observed the nova of 1604 and the comet of 1618. In 1628 he is known to have observed a lunar eclipse and a second one together with Schickard in 1630. Mästlin was the first person to publish an account of earthshine, the illumination of the moon by sunlight reflected from the earth.

Largely forgotten today, except in his role as Kepler’s teacher and an early Copernican, Mästlin was viewed in his own lifetime as one of Europe’s leading astronomers and that with justification.

[1] Lesley Murdin, *Under Newton’s Shadow*, *Astronomical Practices in the Seventeenth Century*, Adam Hilger Ltd., Bristol and Boston, 1985

If I remember correctly, at one point toward the end of his life Kepler experienced increasingly close ties with the Jesuits, culminating with the gift of Zucchi’s telescope at the urging of Fr. Guldin. In your knowledge was this before or after the cooling with his teacher? (That is, was it a potential cause or consequence?)

Kepler knew Zucchi personally and the gift of the telescope was direct, although suggested by Guldin, from one friend to another at a time when Kepler was in financial difficulties. Kepler never had a bad relationship with the Jesuits and existed quite harmoniously with them during his years in Prague. When Giovanni Antonio Magini died in 1617, the Jesuits tried to persuade Kepler to take his chair for astronomy at the University of Bologna, even going so far as to ensure him that he did not need to convert to Catholicism. Kepler, I think wisely, declined the offer. I don’t think that Kepler’s relationship with the Jesuits played a role in his relationship with Mästlin.

Thanks, to be precise I was wondering whether Mästlin not only was displeased with

“Kepler’s sympathy for other religious viewpoints”but with his friendly relationship with the Catholic Jesuits tooI’m afraid there is no evidence at all that it was Maestlin who persuaded Kepler to take the schoolteacher job in Graz. On the contrary, Kepler’s autobiographical notes in Chapter 7 of his Astronomia Nova strongly suggest otherwise. If you read these notes, you will find various references to Maestlin: “… the additional goads which my teacher Maestlin gave me towards embracing the rest of astronomy …and in that man’s prefatory letter …”, and “I saw that Maestlin , too, held it [Rheticus’s Narratio] in great esteem” and “…his untimely promise…”.

But when it comes to the reason for his departure to Graz, he says “I was driven forth to take it by the authority of my teachers”. No mention of Maestlin. None at all. Yet surely, given his other references to Maestlin, he would have said Maestlin if by “my teachers” he had in fact meant Maestlin. Far more likely that he was instead referring to other, unnamed, teachers.

Nor is it the case that Maestlin persuaded Kepler to take the teaching post in Graz. The fact is that Kepler had no choice in the matter, even though he “protest[ed] loudly” about the decision.

And finally, it is highly unlikely that Maestlin taught Copernicanism as literally true (as distinct from useful) in his lectures, given that the Lutheran church at the time was still hostile to Copernicanism.

Nor is it the case that Maestlin persuaded Kepler to take the teaching post in Graz. The fact is that Kepler had no choice in the matter, even though he “protest[ed] loudly” about the decision.Kepler was perfectly free to refuse the position in Graz. However, if he had chosen to do so, as a stipendiary he would have been ex-matriculated from the university and required to repay his stipend.

And finally, it is highly unlikely that Maestlin taught Copernicanism as literally true (as distinct from useful) in his lectures, given that the Lutheran church at the time was still hostile to Copernicanism.I did not claim that Mästlin taught Copernicanism as literally true. In fact is known that Mästlin’s own attitude to heliocentricity changed between his acquisition of

De revolutionibusin 1570 and his observation of the comet of 1577. Initially he only regarded it as mathematically interesting, his observations of the comet convinced him that it was real.There was never an official Lutheran Church opinion on Copernicanism. Despite Melanchthon’s own rejection of heliocentricity, graduates from Wittenberg of both Melanchthon and his son in law Peucer analysed, discussed and taught Copernicus’ theory as a mathematical, i.e. instrumental, model in several German universities in the later part of the sixteenth century.

Kepler left Tübingen for Graz in 1594. As a stipendiary of the Duchy of Wurttemberg he remained a life long servant of the court. As such he was required to obtain permission from the university for any book that he intended to publish. In 1596 his

Mysterium Cosmographicumwas published with the permission of the university. An openly Copernican book with Rheticus’, equally openly Copernican,Naratio Primaas an appendix and a preface by Mästlin confining his commitment to a realist Copernicanism.