Michael Maestlin (also Mästlin, Möstlin, or Moestlin) (30 September 1550, Göppingen – 20 October 1631, Tübingen) was a German astronomer and mathematician, known for being the mentor of Johannes Kepler. He was a student of Petrus Apianus and was known as the teacher who most influenced Kepler. Maestlin was considered to be one of the most significant astronomers between the time of Copernicus and Kepler.
Early Life and Family
Maestlin was born in 1550 in Göppingen, a small town in Southern Germany, about 50 kilometers east of Tübingen. The son of Jakob Maestlin and Dorothea Simon, Michael Maestlin was born into a Protestant family. Maestlin had an older sister named Elisabeth and a younger brother named Matthäus. The original family name of the Maestlin was Leckher or Legecker and they lived in the village of Boll, just a few kilometers south of Göppingen (Decker 103). In his autobiography, Maestlin recounts how the family name of Legecker became Mästlin. He claims that one of his ancestors was given this as a nickname when an old blind woman touched him and exclaimed “Wie bist du doch so mast und feist! Du bist ein rechter Mästlin!” This roughly translates to “How are you so large and plump? You rightly are a fatso!"
Maestlin married Margarete Grüniger on April 9, 1577. There is little information on his children from this marriage. However, it is known that he had at least three sons, Ludwig, Michael and Johann Georg, and at least three daughters, Margareta, Dorothea Ursula and Anna Maria. In 1588, Margarete died at the age of 37, potentially due to complications from child birth. This untimely death left several children under Maestlin’s care and could have influenced his decision to remarry the following year. In 1589, Maestlin married Margarete Burkhardt. Maestlin and Burkhardt had eight children together. In a 1589 letter to Johannes Kepler, Maestlin recounts how the death of his month-old son, August, deeply troubled him.
In 1565, when Michael was around 15 years old, he was sent to the nearby Klosterschule in Königbronn. In 1567, Michael was transferred to a similar school in Herrenalb. Upon finishing his education at Herrenalb, Maestlin enrolled in university. On December 3, 1568, Maestlin matriculated into the University of Tübingen. He obtained his Baccalaureate in 1569 and his Master’s degree in 1571. In letters sent to Maestlin regarding his qualifications, it was revealed that he graduated summa cum laude and ranked third in his graduating class of twenty.  During the time he spent on earning his Master's degree, Maestlin studied under Philipp Apian. It is not certain, but it is believed that Apian taught courses on Frisius's Arithmetic, Euclid's Elements, Proclus's Sphera, Peurbach's Theoricae Novae Planetarus, and the proper use of geodetic instruments.  It is believed that Apian's teachings had an influence on Maestlin's paper on sundials as the contents of this essay involved elements of structured celestial globes and maps.
In 1584, Maestlin was named Professor of Mathematics at Tübingen. He was elected Dean of the Arts Faculty for the following terms: 1588-89, 1594-95, 1600-01, 1607-09, 1610-11, 1615, 1623, and 1629. Maestlin taught trigonometry and astronomy. It was very likely that he used his book Epitome Astronomiae in his lectures.
In 1576, he was sent to be a deacon at the Lutheran Church in Backnang, a town about 30 kilometers Northwest of Göppingen. While in Backnang, Maestlin observed the comet of 1577. During his observations of the comet, Maestlin was unable to find any perceptible parallax. As a result, he concluded that the comet was not a sub-lunar body, but rather a supra-lunar body. Maestlin’s treatise on the comet was dedicated to Duke Ludwig of Württemberg. Maestlin served as the Duke’s chief scientific adviser from 1577-1580. It was in this 1579 discussion that Maestlin announced his .
Maestlin studied theology, mathematics, and astronomy/astrology at the University of Tübingen—the Tübinger Stift. (Tübingen was part of the Duchy of Württemberg.) He graduated as magister in 1571 and became in 1576 a Lutheran deacon in Backnang, continuing his studies there.
In 1580 he became a professor of mathematics, first at the University of Heidelberg, then at the University of Tübingen, where he taught for 47 years from 1583. In 1582 Maestlin wrote a popular introduction to astronomy.
Among his students was Johannes Kepler (1571-1630). Although he primarily taught the traditional geocentric Ptolemaic view of the solar system, Maestlin was also one of the first to accept and teach the heliocentric Copernican view. Maestlin corresponded with Kepler frequently and played a sizable part in his adoption of the Copernican system. Galileo Galilei's adoption of heliocentrism was also attributed to Maestlin.
Michael Maestlin was one of the very few astronomers that fully adopted the Copernican hypothesis, that proposed that the Earth was a planet and that it moved around the sun. Maestlin reacted to the thought of distant stars spinning around a fixed earth every 24 hours and taught everything that he could about Copernicus to Kepler. 
Michael Maestlin also published a treatise and gave a short piece on the nova of 1572. This nova was called the Nova of Cassiopeia. It fascinated and intrigued lots of people, including astronomer Tycho Brahe. However, it was said that Maestlin’s treatise was practically similar to Tycho’s treatise, De Stella Nova, which was published about three months later.
In 1580, Maestlin observed another comet and began to gather up some ideas on how it formed. Nine years later in 1589, Maestlin shared his conclusions about the appearance of the comet with his friend the astrologer, Helisaeus Roselin, who said that the moon was located in front of the Great Comet of 1577, Also this same year, Maestlin published a dissertation on the fundamental principles of astronomy and the first edition of his book Epitome Astronomiae (Epitome of Astronomy). Epitome Astonomiae consisted of six editions and used works like Ptolemy’s famous geocentric model to create his descriptions of astronomy.
The preface in the 1596 republication of Rheticus' Narratio Prima was also written by Maestlin. This preface was an introduction to the work of Copernicus. Additionally, Maestlin made many contributions to tables and diagrams in Kepler’s Mysterium Cosmographicum, adding a treatise together with an introduction of his own. A discussion of the great sphere and the lunar sphere, as well as more discussion and conclusions to his descriptions of the Copernican planetary theory was also added by Maestlin in Kepler’s book.
While Maestlin had many interests like calendar reform and mathematics, he was above all, an astronomer. He spent lots of time researching the sun, moon, and eclipses. His 1596 work, Disputatio de Eclipsibus is almost entirely about the sun and the moon and is often referred to in Kepler's 1604 work, Astronomiae pars optica . In 1587, Maestlin published a manuscript entitled Tabula Motus Horarii in which he gives the daily motion of the sun in hours and minutes with its positions in two-minute intervals. There are a few other tables he published that gives equivalent information but in degrees, minutes, and seconds. In 1613, Maestlin obtained his first telescopes. In a letter to Kepler, Maestlin says he was unable to view the satellites of Saturn or the phases of Venus, however, he was able to see the moons of Jupiter.
Notable astronomical observations
- Catalogued the Pleiades cluster on 24 December 1579. Eleven stars in the cluster were recorded by Maestlin, and possibly as many as fourteen were observed.
- Occultation of Mars by Venus on 13 October 1590, seen by Maestlin at Heidelberg.
In Jules Verne's Cinq semaines en ballon (Five Weeks in a Balloon) the character of Joe, the manservant, is described as enjoying, "in common with Moestlin, Kepler's professor, the rare faculty of distinguishing the satellites of Jupiter with the naked eye, and of counting fourteen of the stars in the group of Pleiades, the remotest of them being only of the ninth magnitude."
- Siegmund Günther (1884), "Maestlin: Michael M.", Allgemeine Deutsche Biographie (ADB) (in German), 20, Leipzig: Duncker & Humblot, pp. 575–580
- Volker Bialas (1987), "Mästlin, Michael", Neue Deutsche Biographie (NDB) (in German), 15, Berlin: Duncker & Humblot, pp. 644–645
- Granada, Miguel A. (February 2014). "Michael Maestlin and His Unpublished Treatise on the Nova of 1604". Journal for the History of Astronomy. 45 (1): 91–122. doi:10.1177/002182861404500106. ISSN 0021-8286.
- Jarrell, Richard A. (1972). "The Life and Scientific Work of the Tubingen Astronomer Michael Maestlin" – via Pro Quest.
- Decker, Martin (1939). Blatter für Württembergische Familienkunde. pp. 102–104.
- Steiff, Karl (1892). Der Tuebingen Professor der Mathematik und Astronomie Michael Maestlin. pp. 49–64.
- Die Matrikeln der Universitat Tübingen 1477-1817. 1906. p. 487.
- Rössler, Hellmuth (1953). Biographisches Wörterbuch zur deutschen Geschichte. Munich. p. 457.
- Kuhn, Thomas (1985) . The Copernican Revolution. Harvard University Press. p. 187. ISBN 978-0-674-17103-9.
- Smolka, Josef: Michael Mästlin and Galileo Galilei. (German Title: Michael Mästlin und Galileo Galilei) , 2002 Verlag Harri Deutsch, Frankfurt am Main, In the earlier literature it is incorrectly claimed that Mästlin, when travelling through Italy, converted Galilei to copernicanism. We know today that Galilei was first introduced to Copernicus' work through Christian Wursteisen. Adsabs.harvard.edu
- J J O'Connor and E F Robertson, The Golden ratio, 2001, The first known calculation of the golden ratio as a decimal was given in a letter written in 1597 by Michael Maestlin, at the University of Tübingen, to his former student Kepler. He gives "about 0.6180340" for the length of the longer segment of a line of length 1 divided in the golden ratio. The correct value is 0.61803398874989484821... The mystical feeling for the golden ratio was of course attractive to Kepler, as was its relation to the regular solids. History.mcs.st-andrews.ac.uk
- Calinger, Ronald (2000). "Review of Kepler's TÃ¼bingen: Stimulus to a Theological Mathematics". The Catholic Historical Review. 86 (1): 128–129. doi:10.1353/cat.2000.0127. JSTOR 25025682.
- GINGERICH, OWEN (2011). "Galileo, the Impact of the Telescope, and the Birth of Modern Astronomy". Proceedings of the American Philosophical Society. 155 (2): 134–141. JSTOR 23056830.
- Grafton, Anthony (1973). "Michael Maestlin's Account of Copernican Planetary Theory". Proceedings of the American Philosophical Society. 117 (6): 523–550. JSTOR 986463.
- Winnecke (December 1878). "On the Visibility of Stars in the Pleiades with the Naked Eye". Monthly Notices of the Royal Astronomical Society. XXXIX. #2 (2): 146–148. Bibcode:1878MNRAS..39..146W. doi:10.1093/mnras/39.2.146.
- Albers, Steven C. (March 1979). "Mutual Occultation of Planets". Sky and Telescope. 57. #3: 220.
- MacTutor Biography of Michael Mästlin
- Michael Maestlin in the German National Library catalogue
- Complete translated text of Five Weeks in a Balloon from Project Gutenberg (English)
- Online Galleries, History of Science Collections, University of Oklahoma Libraries High resolution images of works by and/or portraits of Michael Maestlin in .jpg and .tiff format.