Christopher Clavius

Christopher Clavius ​​(* 1537 or 1538 possibly as Christoph Clau or key in or near Bamberg, † February 6, 1612 in Rome) was a mathematician and a Jesuit priest at the Collegio Romano. Called by his contemporaries " Euclid of the 16th century ," he became famous by the audit conducted under his expert direction calendar reform to the Gregorian calendar, the 1582 with the Bull Inter gravissimas by Pope Gregory XIII. was decreed. Clavius ​​relied to a draft reform of Aloysius Lilius, who had already died in 1576.


Christoph key came from Bamberg and translated his family name in the old custom of scholars into Latin, so that he was called Clavius ​​. In 1555 he joined the Society of Jesus, where he received his education. 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. Later, he studied theology at the Collegio Romano in Rome and then taught there all his life mathematics. Clavius ​​wrote several books on mathematics and thus contributed to the dissemination of mathematics. A common comment to Euclid ( 1574 ) and the most important astronomical textbook of the late Middle Ages, the Sphaera of John de Sacrobosco comes from him. In 1608 he wrote a textbook on algebra. His works have been repeatedly published after his death in re- runs, his annotated translation of Euclid's Elements to the year 1717.

He was the founder of scientific work at the Vatican Observatory and also designed astronomical instruments such as sundials. To this end, Clavius ​​described in his Fabrica et usus instrumenti ad horologiorum descriptionem peropportuna 1586 a ruler to mark out the lines on the sundial. Clavius ​​at the Collegio Romano and his students were talking collegially - friendly relationship with Galileo Galilei and corresponded with him about new discoveries with the telescope; the phase as Venus discovered the Roman Jesuit independently by Galileo and perhaps even before him. From the School of Clavius ​​was also the first missionary to China the Jesuits, Matteo Ricci, out.

One unconfirmed story by Clavius ​​to have during a visit of the seven churches found in 1612 by a crazed oxen on a road near Rome death. The monthly correspondence for the transport of earth and sky customer from the October 1813 this version was ' the end of life Clavius ​​but rejected as false and baseless. The message may be due to a misunderstood poem that had been written Clavius ​​honor after his death. It says: " The sun was in Taurus, and was darkened " All the other historians reported nothing of this spectacular form of death. . On the contrary, Clavius ​​wrote on January 1, 1612 a letter to the Bamberg Prince- Bishop Johann Gottfried von Aschhausen in which he reported that tie him his old age and the consequent discomfort to the bed. And since Clavius ​​was hardly dead four weeks later, he could have done in his poor condition hardly visiting the seven churches of Rome.

Performance of existing

Gregorian calendar reform

The Gregorian calendar reform was essentially designed by him on the basis of the proposals of the late Aloysius Lilius 1576 and carried out. It is valid until today. On October 4, 1582 was followed by October 15. All that is divisible by four years (except those ending in "00", they are only leap years if they are divisible by 400 ) leap years. The reform met with some strong resistance (it was only much later implemented in the Protestant and Orthodox countries ) and was scientifically defended by him. To this end, he published the two works Novi Romani calendarii apologia (Rome, 1588) and Romani calendarii a Gregorio XIII restituti explicatio (Rome, 1603).

Decimal point

Clavius ​​used 1593 in the sine tables his astrolabe as the decimal separator between the integer part and the tenth of a point. According to Carl Boyer, he was the first person who used the decimal point with a clear idea of its meaning. Based on current knowledge Francesco Pellos came to him in 1492 already so before, but he fell short of his works such as the spread Clavius ​​.


  • The lunar crater Clavius ​​reminded of him.
  • The Clavius ​​-Gymnasium in Bamberg is named after him.
  • In Bamberg, An der Universität 2, the former Jesuit College, a plaque is attached.
  • In Bamberg the Claviusstraße exists.