Johannes Regiomontanus

1436-1476

German Astronomer and Mathematician

Johannes Regiomontanus played a key role in reforming astronomical studies in fifteenth-century Europe by emphasizing and acting on the need for new and improved observations over those of the ancients. He also introduced Arabic algebraic and trigonometric methods to Europe, thus providing a systematic basis for their further development.

Regiomontanus, whose real name was Johann Müller, was born on June 6, 1436, in Königsberg, Franconia. The name of his birthplace means "King's Mountain," and in accordance with the practice of the day his parents adopted the Latinized version of this name—Joannes de Regio monte—from whence Regiomontanus was derived. He studied dialectics at Leipzig sometime around 1448. He was then drawn to the University of Vienna by the reputation of the astronomer Georg von Purbach (1423-1461). Regiomontanus matriculated there in 1450 and after receiving his bachelor's (1452) and master's degrees (1457) joined the Vienna faculty.

European astronomical work of the Middle Ages, with the exception the efforts of Alfonso X (1223-1284) and his assistants, amounted to little more than the collection and reorganization of Arabic and ancient Greek material. No new observations of importance were undertaken, and by the mid-fifteenth century the Alfonsine Tables (1252) were sorely in need of revision. Purbach pointed out to Regiomontanus the inaccuracies of the Tables as well as the need for better translations of Greek texts. Though his knowledge of ancient Greek left much to be desired, Puerbach attempted to produce a revised and corrected Latin verion of Ptolemy's (fl. second century a.d.) Almagest. Though he did not live to finish the project, he pledged Regiomontanus to see it to completion.

In 1461 Regiomontanus traveled to Italy in search of early Greek scientific manuscripts. While there he finished the Epitome of Astronomy. The work contained, in addition to the Purbach-Regiomontanus translation of Ptolemy's work, critical commentary, revised computations, and additional observations. Though not printed until 1496, 20 years after Regiomontanus's death, the work was a great success and attracted the attention of a young Nicolaus Copernicus (1473-1543). Struck by the errors in Ptolemaic lunar theory revealed by Regiomontanus, Copernicus went on to develop his heliocentric view of a Sun-centered Solar System.

While in Italy, Regiomontanus completed much of De triangulis omnimodis, which appeared posthumously in 1533. This work represents the first systematic treatment of trigonometry presented independently of astronomy. Together with his Tabulae directionum it was the primary means whereby Arabic algebraic and trigonometric methods were reintroduced to Europe. In De triangulis, Regiomontanus developed the earliest statement of the cosine law for spherical triangles; the Tabulae directionum, which was primarily an astronomical work, contained a valuable table of tangents.

By 1468 Regiomontanus had returned to Vienna. He then moved to Nuremberg in 1471. There he attracted the wealthy, amateur astronomer Bernard Walther (1430-1504), who provided him with an observatory and work shop. Of the many observations Regiomontanus made while in Nuremberg his most important were of the comet of 1472—later to be known as Halley's comet. This work appears to have been the first attempt to study comets scientifically instead of viewing them merely as objects of superstition. Regiomontanus also established the first press devoted to astronomical and mathematical literature, intending to advance the work of science by providing quality texts free of scribal and printing errors.

In 1475 Regiomontanus traveled to Rome. According to some reports he was summoned by Pope Sixtus IV to assist with the reform of the Julian calendar. Whether or not this is true, nothing substantive along these lines emerged from his trip, for he died on July 8, 1476, quite probably due to the plague that spread after the Tiber overflowed earlier that year.

STEPHEN D. NORTON