Christoph Clavius (1537–1612)

Christoph Clavius image
Portrait of Christoph Clavius (1537–1612).
Credit: Wikipedia.

The Jesuit mathematician and astronomer Christopher Clavius [Clau](1537-1612). Born in Bamberg in 1537, Clavius joined the Jesuit order in 1555, and studied at Coimbra. Clavius was one of the major architect of the Gregorian calendar reform of 1582, and remained professor of mathematics at the Jesuit's Collegio Romano until his death on February 6, 1612.

Title page of Clavius' commentary
Title page of Clavius' commentary on the Spheres of Sacrobosco, first published in 1570. Revised editions appeared in 1581, 1585, 1593, 1607,and 1611.

In 1570 Clavius wrote what was to become one of the most influential textbook on astronomy of its days, in the form of a commentary on the so-called Spheres of Sacrobosco (see "Clavius' Spheres" below). In the catholic world, this was the textbook for three generations of astronomers, including Galileo Galilei, and most particularly for Jesuit astronomers throughout the world. In later editions of his book Clavius pronounced himself relatively favorably on the Copernican system as a mathematical model, but to the end of his life rejected its physical reality. Until Galileo's condemnation in 1633, this was also the official position of the Roman ecclesiastic authorities.

Clavius was chief astronomer at the Jesuit's "Collegio Romano" at the time of Galileo's first telescopic discoveries, and was still quite active despite his advancing age. He pronounced himself favorably concerning the physical reality of most of these telescopic observations. His doing so effectively silenced the first wave of opposition to Galileo. He did not agree with all of Galileo's interpretations however, and in particular remained staunchly opposed to the notion of mountains on the Moon.

Clavius' Spheres

Clavius' Spheres, along with his influential commentary on Euclid's Elements, was regularly reprinted for many decades after his death in 1612. The book is basically a presentation of Ptolemaic astronomy, although in later editions the "Tychonian" and "Copernican" planetary systems are also discussed.

Bibliography:
Lattis, J. 1994, Between Copernicus and Galileo: Christopher Clavius and the collapse of Ptolemaic Astronomy (Chicago: The University of ChicagoPress).