Petrus Gaszowiec, (c.1425, Rozmierz–1474, Kraków) (also known as Piotr Gaszowiec, Petro Gassoviecz, Petr Gaschowietz, Petrus de Silesia, Petrus Strzelec) was a Polish astrologer, doctor and professor at the Kraków Academy. Petrus Gaszowiec probably began his education at the local school in Strzelce Opolskie and subsequently entered the Kraków Academy in the winter semester of 1446. He became a baccalarius in 1448 and in 1452 became a doctor of the arts. He was a student of several other great minds of his era, among them, Jan of Ludzisko, Marcin Król of Żurawice, and Andrzej Grzymała from Poznań. In 1452 he left for Perugia in Italy, where he studied medicine and astronomy. He continued these studies in Cologne in 1454–1455, under the supervision of Gerard of Hamnont. Gaszowiec finally returned to Kraków in 1456 and took up a post as the court doctor of Casimir IV Jagiellon. In that same year he also joined the faculty of medicine at the Kraków Academy and began lecturing there as a doctor of medicine. He served as dean of the medical faculty in 1459 and 1462, as well as rector of the whole academy in the winter of 1464–65 and the summers of 1465 and 1470. In 1459 he married a wealthy townswoman named Katarzyna Homanówna, and together they had nine children. Gaszowiec also pursued astronomical research, leaving behind works used by the subsequent generation of astronomers, including Nicholas Copernicus. Among other texts he wrote and constructed numerous astronomical tables. In 1453, Gaszowiec worked out a catalogue of fifteen fixed stars. The Almanach Cracoviense ad annum 1474, which is the oldest surviving document printed on Polish soil, was most likely written by Gaszowiec. It was published by Kasper Straube, a Bavarian printer who worked in Kraków from 1473 to 1476. Similar to other calendars and almanacs of the era, the lists church holy days alongside astronomical data. It also contains information such as the most astrologically propitious days for letting blood, according to the age and health of the patient. The only surviving copy of the document is held by the Jagiellonian Library. In addition to his medical and astronomical pursuits, Gaszowiec also dabbled in magic. It is probable that he was partly responsible for the copying of the Picatrix and for bringing that text from Italy to Poland. The book, which was likely written by the Arabic author al-Majriti, discusses such topics as the