Christoph Clavius

Christopher Clavius
Christopher Clavius.
Born	25 March 1538 Bamberg, Bavaria, Holy Roman Empire
Died	February 2, 1612(1612-02-02) (73 years) Rome, Papal States
Nationality	German
Fields	Mathematician, astronomer
Alma mater	University of Coimbra
Known for	Gregorian calendar
Influences	Euclid, Pedro da Fonseca, Pedro Nunes

Christopher Clavius (25 March 1538 – 3 February 1612) was a German Jesuit mathematician and astronomer who modified the proposal of the modern Gregorian calendar after the death of its primary author, Aloysius Lilius. Clavius would later write defences and an explanation of the reformed calendar, including an emphatic acknowledgement of Lilio's work. In his last years he was probably the most respected astronomer in Europe and his textbooks were used for astronomical education for over fifty years in and even out of Europe.

Little is known about Clavius' early life other than the fact that he was born in Bamberg in either 1538 or 1537. His given name is not known to any great degree of certainty—it is thought by scholars to be perhaps Christoph Clau or Klau. There are also some who think that his taken name, "Clavius", may be a Latinization of his original German name, suggesting that his name may have been "Schlüssel" (German for "key", which is "clavis" in Latin).

Clavius joined the Jesuit order in 1555. He attended the University of Coimbra in Portugal, where it is possible that he had some kind of contact with the famous mathematician Pedro Nunes (Petrus Nonius). Following this he went to Italy and studied theology at the Jesuit Collegio Romano in Rome. In 1579 he was assigned to compute the basis for a reformed calendar that would stop the slow process in which the Church's holidays were drifting relative to the seasons of the year. Using the Prussian Tables of Erasmus Reinhold and building on the work of Aloysius Lilius, he proposed a calendar reform that was adopted in 1582 in Catholic countries by order of Pope Gregory XIII and is now the Gregorian calendar used worldwide.

Within the Jesuit order, Clavius was almost single-handedly responsible for the adoption of a rigorous mathematics curriculum in an age where mathematics was often ridiculed by philosophers as well as fellow Jesuits like Benito Pereira. In logic, Clavius' Law (inferring of the truth of a proposition from the inconsistency of its negation) is named after him.