Georg Joachim de Porris, also known as Rheticus (; 16 February 1514 – 4 December 1574), was a mathematician, astronomer, cartographer, navigational-instrument maker, medical practitioner, and teacher. He is perhaps best known for his trigonometric tables and as Nicolaus Copernicus's sole pupil. He facilitated the publication of his master's De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres).
Surname Rheticus was born at Feldkirch in the Archduchy of Austria. Both his parents, Georg Iserin and Thomasina de Porris, were of Italian heritage and possessed considerable wealth, his father being the town physician as well as a government official. He was educated by his father until the age of 14 when Georg (Iserin) abused the trust of many of his patients, stealing belongings and money from their homes. In 1528 he was convicted and executed for his crimes, and as a result his family was stripped of their surname. The family adopted the mother's maiden name: de Porris. Later as a student at the University of Wittenberg, Georg Joachim adopted the toponym Rheticus, a form of the Latin name for his home region, Rhaetia, a Roman province that had included parts of Austria, Switzerland and Germany. In the matriculation list for the University of Leipzig his family name, de Porris, is translated into German as von Lauchen. The lunar crater Rhaeticus as well as asteroid 15949 Rhaeticus were named for him.
Patrons After Georg Iserin's death, Achilles Gasser took over his medical practice, helping Rheticus to continue his studies and supporting him, eventually going so far as to furnish him with a letter of introduction to Philipp Melanchthon, a theologian and educator who would become a major patron, having reorganized the whole educational system of the Lutheran Protestant parts of Germany, reforming and founding several new universities during the Reformation. This relationship in particular would soon serve him well as Melanchton possibly chose him specifically for the University of Wittenberg. Rheticus studied at Feldkirch, Zürich and Wittenberg where he received his M.A. in 1536, after which Melanchthon appointed Rheticus as professor of the lower mathematics, arithmetic and astronomy, at the Wittenberg University. Two years later, Melanchthon arranged a two-year leave for Rheticus to study with noted astronomers. Leaving Wittenberg in October 1538, he first went to Nuremberg to visit the professor of mathematics at the Eigidien Oberschule, Johannes Schöner. In Nuremberg he also made the acquaintance of other mathematicians such as Georg Hartmann and Thomas Venatorius as well as the printer-publisher Johannes Petreius. During his journey, probably in Nuremberg, Rheticus heard of Copernicus and decided to seek him out. It is unknown whether he had access to Copernicus' Commentariolus, an unsigned, unpublished outline of Copernicus' revolutionary heliocentric theory that Copernicus distributed to friends and colleagues three decades before he published De revolutionibus, prior to this or perhaps on consulting Schöner who is believed to have persuaded him. From Johannes Petreius Rheticus was given works by Regiomontanus and others, intended as presents for Copernicus. He went on to Peter Apian at the University of Ingolstadt and Joachim Camerarius at the University of Tübingen, then to his hometown when Rheticus would present Gasser with an edition of Sacrobosco. From Feldkirch he set out on his journey to visit Copernicus in Frombork.
Copernicus
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