little is known of Remus Quietanus, a privileged witness of the Copernican revolution. But he is not a passive observer. In his correspondence with Kepler, he took part in astronomical debate and asked questions that fitted exactly with the issues of his time: the calculation of longitudes, the nature of comets, the dimension of planets, their distances to the sun and especially the distance from the Earth to the Sun (Astronomical unit). On the last point, he had a better intuition than Kepler who gave an estimation of 3400 of Earth radius. Remus Quietanus proposed 14,000. Not until 1685 did Christiaan Huygens suggest a more accurate estimation (around 23,500 of Earth radius). Bibliography Max Caspar, Johannes Kepler Gesammelte Werke, 1937, volumes 16, 17 and 18. Klaus-Dieter Herbst, Biobilographisches Handbuch der Kalendermacher 1550-1750 Remus Quietanus, Johannes, Institut Deutsche Presseforschung, 2017. Klaus-Dieter Herbst, « Die erstmalige Benutzung von Keplers Rudolphinischen Tafeln für die Herstellung eines Schreibkalenders », Acta Historica Astronomiae, 40, 2010, p. 160-169. Jacques Mertzeisen, Jean-Pierre Luminet, Homage to Quietanus, Inference, International Review of Science, 2017. Notes References 17th-century German astronomers 17th-century German physicians German astrological writers Physicians from Thuringia 1588 births 1654 deaths Scientists from Thuringia People from Wartburgkreis