In 1580, Maestlin became a professor of mathematics, first at the
University of Heidelberg, and later at the University of Tübingen, where he taught for 47 years starting in 1583. In 1582, he authored a popular introduction to astronomy. While teaching at the university, Maestlin primarily taught traditional Ptolemaic astronomy in his courses. However, he introduced Copernican heliocentric astronomy to his advanced students, fostering a deeper understanding of the revolutionary model. While Maestlin had diverse interests, including calendar reform and mathematics, he was, above all, an astronomer. He dedicated much of his research to studying the Sun, the Moon, and eclipses. His 1596 work,
Disputatio de Eclipsibus, focuses almost entirely on the Sun and the Moon and is frequently referenced in Kepler's 1604 work,
Astronomiae Pars Optica. Although Maestlin primarily taught the traditional
geocentric Ptolemaic model of the Solar System, he was one of the earliest proponents of the
heliocentric Copernican view and introduced it to his advanced students. The first known calculation of the (inverse)
golden ratio as a decimal, approximately 0.6180340, was made by Maestlin in 1597. He included this calculation in a letter to Kepler about the
Kepler triangle. Maestlin was one of the few astronomers of the 16th century to fully embrace the
Copernican hypothesis, which proposed that the Earth was a planet that moved around the Sun. In 1570, he acquired a copy of Copernicus' seminal work,
De revolutionibus orbium coelestium (Maestlin's personal copy, containing his handwritten notes in the margins, is preserved in the municipal library of
Schaffhausen). In his notes, Maestlin responded to the concept of distant stars revolving around a fixed Earth every 24 hours. He also shared everything he could about Copernicus' work with Kepler. In accepting the Copernican view of the Solar System, Maestlin believed that the "movement of commutation" (or "parallactic motion") of the superior planets—those farther from the Sun than Earth—and the lack of parallactic motion in the supernova meant that the supernova must have occurred outside the planetary spheres, in the realm of
fixed stars. This contradicted the previous understandings of the Ptolemaic and Aristotelian models. Maestlin also concluded that the nova provided evidence for the heliocentric Solar System. He argued that unless people concede that comets can exist in the stellar orb, which has an immense altitude and an unknown extent, the distance between the Sun and the Earth, as described by Copernicus, remains incomparable. This
Type Ia supernova, known as
SN 1572, occurred in the constellation Cassiopeia and was the first galactic supernova to be observed in Europe.
Great comet of 1577 In accordance with the Copernican view of the heavens, Johannes Kepler calculated that there were empty spaces between the planetary orbits, and Maestlin suggested that these spaces might be where comets frequently occur.
Role in Kepler's Mysterium Cosmographicum Maestlin also supervised and made significant contributions to the tables and diagrams in Kepler's
Mysterium Cosmographicum, published in 1596. Maestlin and Kepler communicated through letters about the book, and some of these letters formed the foundation of Maestlin's appendix to the publication. This appendix focused on Copernican planetary theory, using the values from
Erasmus Reinhold's Prutenic Tables to determine a set of planetary distances. The appendix was titled "On the Dimensions of the Heavenly Circles and Spheres, According to the Prutenic Tables After the Theory of Nicolaus Copernicus" and was intended to address "the needs of a hypothetical educated reader" while answering some of the questions Kepler had raised in the book. In addition to his appendix, Maestlin also contributed his own understanding of Nicolaus Copernicus' geometry to Kepler's book. In their correspondence, they discussed topics such as the inaccuracies in the values that Copernicus used when calculating the spheres of the cosmos. However, these diagrams caused a misunderstanding that lasted for centuries, as Maestlin did not clarify whether the planets were meant to move along the lines of the circles representing his planetary system or within the spaces he had drawn.
Kepler's Supernova In 1604, Maestlin was one of the first astronomers to observe the 1604 Supernova (later known as
Kepler's Supernova) on 9 October. He made his observations visually, without instruments, but did not immediately publish them. Instead, he began working on a treatise titled
Consideratio Astronomica inusitatae Novae et prodigiosae Stellae, superiori 1604 anno, sub initium Octobris, iuxta Eclipticam in signo Sagittarii vesperi exortae, et adhuc nunc eodem loco lumine corusco lucentis (Astronomical Consideration of the Extraordinary and Prodigious New Star that Appeared Near the
Ecliptic in the Sign of Sagittarius One Evening in Early October in the Preceding Year 1604, and Continues to Shine in the Same Place with a Tremulous Light). He intended to publish the treatise in the following years. Maestlin began working seriously on it in 1606; however, it was never fully completed. ==Christianity==