1. Christopher Clavius, was a Jesuit German mathematician, head of mathematicians at the, and astronomer who was a member of the Vatican commission that accepted the proposed calendar invented by Aloysius Lilius, that is known as the Gregorian calendar.
Little is known about Christopher Clavius' early life, with the only certain fact being that he was born in Bamberg in either 1538 or 1537.
Christopher Clavius attended the University of Coimbra in Portugal, where it is possible that he had some kind of contact with the famous mathematician Pedro Nunes.
Christopher Clavius was ordained in 1564, and 15 years later 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.
In logic, Christopher Clavius' Law is named after him.
Christopher Clavius used the decimal point in the goniometric tables of his astrolabium in 1593 and he was one of the first who used it in this way in the West.
Christopher Clavius wrote a commentary on the most important astronomical textbook of the late Middle Ages, De Sphaera of Johannes de Sacrobosco.
The commentary by Christopher Clavius was one of the most influential astronomy textbooks of its time and had at least 16 editions between 1570 and 1618, with Christopher Clavius himself revising the text seven times and in each case greatly expanding it.
Christopher Clavius was treated with great respect by Galileo, who visited him in 1611 and discussed the new observations being made with the telescope; Clavius had by that time accepted the new discoveries as genuine, though he retained doubts about the reality of the mountains on the Moon and said he could not see the four Jupiter's satellites through the telescope.
However, in 1580 in his document titled Ordo servandus in addiscendis disciplinis mathematicis, Christopher Clavius described a detailed curriculum for mathematics to have the College officially recognize the Academy.
Christopher Clavius's request was eventually denied, but nonetheless he was given the title of Professor of Mathematics.
Christopher Clavius made another attempt in 1586 to establish the Academy as an official course at the Collegio Romano, but there was opposition from the philosophers at the College.
Christopher Clavius taught the advanced course within the Academy, but little is known about his specific teachings and work as a professor during his time at the College.