Today marks the anniversary of the birth in 1436 of a German mathematician and astronomer who is usually known by the Latin name Regiomontanus. His life and career afford an excellent illustration of the multinational scholarly culture of the Middle Ages and Renaissance, facilitated by the use of Latin as a common language.

He was born Johannes Müller in the Bavarian town of Königsberg, which means “King’s Mountain”, “Mons Regius” in Latin, whence his single-word nickname. He is also sometimes known as “Molitor”, Latin for “miller”, the meaning of his German family name. A child prodigy, he began his studies at the University of Leipzig when he was 11, before moving to Vienna, where he obtained his baccalaureate at the age of 16. He soon completed the necessary work to obtain his master’s degree but had to wait until he reached the statutory age of 21 before it could be officially granted. In the latter school, he became a student and friend of Georg von Peuerbach, an important figure in the promotion of classical learning in both Latin and Greek. His teacher was also a mathematician and astronomer, who had traveled in several countries, and been offered professorships at a number of prestigious Italian universities.

In 1460, the Greek cardinal and humanist scholar Basil Bessarion met both the teacher and student when he arrived in Vienna on a diplomatic mission. He encouraged Peuerbach in the work he was doing on Ptolemy’s Almagest, the principal astronomical textbook of the era, but Peuerbach himself died halfway through the project, which he entrusted to Müller on his deathbed. The following year, Bessarion left Vienna, bringing Müller with him. As a cardinal, Bessarion was based in Rome but traveled frequently on the business of the Church. Müller, while continuing to work on the epitome of Ptolemy, improved his knowledge of Greek, and accompanied the cardinal on his travels as a member of his household over the next four years.

In the summer of 1464, he lectured at the Univ. of Padua, but when Pope Paul II died at the end of August, the cardinal had to return to Rome for the Papal election, and Müller went with him. Back in Rome, he met the royal astronomer to the king of Hungary, at whose behest he took up a position in 1467 with the Royal Library in Buda. While in residence there, he wrote some important treatises on various aspects of trigonometry and sine tables.

(A portrait of Regiomontanus; public domain image from Wikimedia Commons.)

In mid-1471, Müller went to the German city of Nuremburg to observe a lunar eclipse, and decided to reside there permanently, as he himself wrote, “… on account of the great ease of all sorts of communication with learned men living everywhere, since this place is regarded as the center of Europe because of the journeys of the merchants.” Here he worked on a variety of astronomical instruments and recorded observation of an unusually bright comet that appeared on Christmas Day and remained clearly visible for two months. He also set up a printing press in his own house so that scientific works could be more readily diffused; Christopher Columbus and Amerigo Vespucci both used printed copies of his work on longitude, the Ephemerides, in their voyages to the New World.

In 1475, Pope Sixtus IV summoned him to Rome to serve as a consultant on a proposed reform of the calendar, another among the many subjects on which he had written, but in the midst of the following year, he died of a plague which broke out in the city. In 1651, the Jesuit priest and astronomer Giovanni Riccioli published his “New Almagest”, an extremely influential general encyclopedia of astronomical knowledge, and named one of the moon’s craters “Regiomontanus” in Müller’s honor, and the crater next to it after his teacher Peuerbach. This nomenclature is still used to this very day.

The lunar craters are named for Regiomontanus and Peuerbach, the latter labeled with the alternative spelling Purbach. Public domain image from Wikimedia Commons.