**Georg Joachim Rheticus** was an Austrian mathematician and astronomer who published the trigonometrical sections of Copernicus's *De Revolutionibus*.

- Rheticus was, therefore, born Georg Joachim Iserin.
- 'De porris' means 'of the leeks' in Italian and, since Rheticus did not consider himself Italian he translated it into German 'von Lauchen' and called himself Georg Joachim von Lauchen.
- He later took the additional name of Rheticus after the Roman province of Rhaetia in which he had been born.
- He helped Rheticus continue his studies and was a strong support to him.
- Melanchthon played a major role in getting Rheticus an appointment to teach mathematics and astronomy at the University of Wittenberg in 1536.
- This appointment, which involved teaching arithmetic and geometry, gave Rheticus a salary of 100 gulden.
- Two years later Melanchthon again used his influence to arrange leave for Rheticus to study with some of the leading astronomers of the day, but his main reason was to visit Copernicus.
- In Nuremberg Rheticus also visited the printer Petreius.
- He then visited Peter Apianus in Ingolstadt, next Joachim Camerarius in Tübingen and then he fitted in a visit to his home town of Feldkirch to visit Achilles Gasser whom he presented with a copy of Sacrobosco.
- In May 1539 Rheticus arrived at Frauenburg in Ermland where he spent about two years with Copernicus.
- In September 1539 Rheticus went to Danzig, visiting the mayor of Danzig, who gave Rheticus some financial assistance to help publish the Narratio Prima or, to give it its full title First report to Johann Schöner on the Books of the Revolutions of the learned gentleman and distinguished mathematician, the Reverend Doctor Nicolaus Copernicus of Toruń, Canon of Warmia, by a certain youth devoted to mathematics.
- Of course Rheticus sent a copy to Schöner and also to Petreius, who found it splendid.
- In August 1541 Rheticus presented a copy of his work on a map of Prussia to Duke Albert of Prussia and the following day he sent him an instrument he had made to determine the length of the day.
- Rheticus knew that Duke Albert had tried unsuccessfully to find out how to compute the time of sunrise.
- Duke Albert replied quickly giving permission for the publication and, at the same time requesting that Rheticus retain his chair.
- In October 1541 Rheticus returned to the University of Wittenberg and there he was elected dean of the Faculty of Arts.
- In early 1541 Rheticus published the trigonometrical sections of Copernicus's De Revolutionibus adding tables of his own giving tables of sines and cosines (although he did not call them by these names).
- Joachim Camerarius, who was head of the University of Tübingen, working with Melanchthon, arranged for Rheticus to be offered a post at the University of Leipzig.
- In 1542 Rheticus was appointed professor of higher mathematics at Leipzig.
- Rheticus remained at Leipzig until 1545 when he again arranged leave to allow him to study abroad.
- Rheticus continued on his travels until, at Lindau, a city in Bavaria on an island in Lake Constance his health broke down and he had severe mental problems during the first half of 1547.
- With Melanchthon's influence Rheticus was made a member of the theological faculty at Leipzig.
- A man of many talents, Rheticus published a calendar and ephemeris of 1550 and also an ephemeris and calendar of 1551.
- Although he was not present to defend himself, Rheticus was sentenced to 101 years in exile.
- Rheticus's important work on trigonometry Opus Palatinum de triangulis uses all six trigonometric functions.
- He gave tables of all these six functions in this major work which was completed and published in 1596 by Valentine Otho many years after Rheticus's death.
- Otho had studied at Wittenberg and then set out to visit Rheticus in a similar way to that in which Rheticus himself had visited Copernicus.
- Given the dramatic and eventful life that Rheticus led it is interesting to think about his personality.

Born 16 February 1514, Feldkirch, Austria. Died 4 December 1574, Kassa, Hungary (now Kosice).

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Analysis, Astronomy, Geometry, Origin Austria

**O’Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive