Christophorus Clavius

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Christophorus Clavius (born March 25, 1538 , possibly as Christoph Clau or key in or near Bamberg , † February 6, 1612 in Rome ) was a mathematician and Jesuit priest at the Collegio Romano . Called "Euclid of the 16th century" by his contemporaries , he became famous above all for the calendar reform to the Gregorian calendar that was carried out under his professional direction , which was introduced in 1582 with the Bull Inter gravissimas by Pope Gregory XIII. was decreed. Clavius ​​implemented a reform draft by Aloisius Lilius , who had died in 1576.

Christophorus Clavius. Engraving by Francesco Villamena , 1606


Only the Latinized form of the name of Clavius ​​from Bamberg is known. In 1555 he joined the Jesuit order and received his education there. Certainly attracted by the reputation of Pedro da Fonseca , who was also known as the "Portuguese Aristotle", Clavius ​​came to the University of Coimbra in Portugal , where Pedro Nunes was his teacher. He later studied theology at the Collegio Romano in Rome and taught mathematics there throughout his life. Clavius ​​wrote several mathematics books, including a commentary on Euclid (1574) and on the most important astronomical textbook of the late Middle Ages, the Sphaera of Johannes de Sacrobosco . In 1608 he wrote a textbook on algebra . His works were reprinted several times even after his death, his annotated translation of Euclid's Elements up to 1717.

He was the founder of the scientific work at the Vatican Observatory and also designed astronomical instruments such as sundials. For this purpose, Clavius ​​described in his Fabrica et usus instrumenti ad horologiorum descriptionem peropportuna of 1586 a ruler to mark the lines on the sundials. Clavius ​​and his students at the Collegio Romano maintained friendly relations with Galileo Galilei and corresponded with him about new discoveries with the telescope; The Roman Jesuits discovered the phase form of Venus independently of Galileo and perhaps even before him. The first Jesuit missionary to China , Matteo Ricci , also emerged from Clavius' school .

According to an unconfirmed narrative, Clavius ​​is said to have been killed by a wild ox on a street near Rome in 1612 while visiting the seven churches of Rome . In the monthly correspondence for the promotion of geography and celestial science from October 1813, however, this version of Clavius' end of life was rejected as false and unfounded. The news may come from a misunderstood poem written in honor of Clavius ​​after his death. It says: "The sun went down in Taurus and was darkened." None of the other historians reported anything of this spectacular death. Rather, on January 1, 1612, Clavius ​​reported to the Bamberg prince-bishop Johann Gottfried von Aschhausen that his old age and the associated complaints tied him to bed. This makes it unlikely that he would have visited the seven churches of Rome in his poor condition.

Existing services

In Sphaeram Ioannis de Sacro Bosco commentarius , 1585

Gregorian calendar reform

The Gregorian calendar reform was essentially designed and implemented by him on the basis of the suggestions made by Aloisius Lilius , who died in 1576 . It is still valid today. October 4, 1582 was followed by October 15. All years divisible by four are leap years (except for those that end in "00", they are only leap years if they are divisible by 400). The reform met with some fierce resistance (it was only implemented much later in the Protestant and Orthodox countries) and was scientifically defended by him. In addition, he published the two writings Novi calendarii Romani apologia (Rome, 1588) and Romani calendarii a Gregorio XIII restituti explicatio (Rome, 1603).

Decimal point

In 1593, Clavius ​​used a point as a decimal separator between the integer part and the tenth in the sine tables of his astrolabe . According to Carl Boyer , this made him the first person to use the decimal point with a clear idea of ​​its meaning. As far as we know today, Francesco Pellos came before him in 1492, but his works did not come close to spreading like Clavius.


The Clavius ​​crater with noticeable rim craters

Individual evidence

  1. Lattis, Christopher Clavius, Dictionary of Scientific Biography
  2. Ralf Kern: Scientific instruments in their time. , Volume 2: From Compendium to Individual Instrument. , Cologne 2010, Walther König Verlag, ISBN 978-3865608666 . P. 255.


Refutatio cyclometriae Iosephi Scaligeri


Web links

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