Johann Ruderauf or Johannes Remus Quietanus (Herda 1588 – Rouffach 1654) was a German astronomer, astrologer and doctor. He maintained correspondence with Galileo Galilei, Johannes Kepler and Giovanni Faber, a pontifical botanist. He is one of the first four observers of transit of Mercury that happened on 7 November 1631. Biography Early life in Thuringia Johann Ruderauf was born on 22 September 1588 in Herda, near Bad Salzungen in Thuringia (Germany). His father Jeremias Ruderauf (or Rudravius) was a pastor and a schoolmaster. In the Julian Calendar, Johann was baptised as a Protestant on 15 September 1588. He enrolled at the University of Jena in 1605. In 1607, he observed the passage of a comet, and then wrote a booklet of some fifty pages titled Gründliche Beschreibung des neuen monstrosischen Sternes, welcher anno Christi 1607 …am hohen Himmel geleichtet, (Accurate description of the new monstrous star that shone in the sky from July 27 to mid-October in 1607), where he proposed an astrological interpretation of this "sign of God". This was actually Halley's comet that did not yet bear the current name. In 1608, he went to Italy. Probably he had never returned to his native country thereafter. Study and work in Italy Johann Ruderauf registered at the University of Padua in 1608, where he studied medicine. There he was also acquainted with Galileo. In Italy, he took up the Latinized name Johannes Remus Quietanus and converted to Catholicism. In 1609, he made a southbound trip to Sicily and Malta. In 1611, he was in Rome, where he sent the first letter to Kepler. In the next years, he studied in the Collegio Romano with professor Christoph Grienberger. Remus Quietanus was well received by the pontifical circle, he befriended a number of cardinals and Giovanni Faber, secretary of the Accademia dei Lincei. He made astronomical observations, especially solar and lunar eclipses, and wrote two pamphlets on this subject. Doctor of Habsburg In 1618, Remus Quietanus went to the court of Archduke Maximilian III of Austria in Innsbruck. There he met Christoph Scheiner. After the death of Maximilian in Vienna on 2 November 1618, Remus Quietanus was appointed the Imperial Doctor, serving Matthias, Holy Roman Emperor, and also his cousin Leopold V, the new Archduke of Austria-Tyrol. In 1619, he met Johannes Kepler in Linz. Witness of the Thirty Years' War In his correspondence with Giovanni Faber(1618-1622), Remus Quietanus reported the