Galileo was appointed to the chair of mathematics at the University of Pisa in 1589.
The appointment marked his transition from an emerging mathematical thinker to a university professor. At Pisa, mathematics included practical subjects such as geometry, mechanics, astronomy, and military engineering—fields that were closely connected in Renaissance education. Galileo’s teaching and investigations increasingly challenged inherited Aristotelian ideas about motion.
He remained at Pisa until 1592, when he moved to the University of Padua in the Venetian Republic. There he taught geometry, mechanics, and astronomy, and developed many of the experiments and arguments that later made him famous. A common mix-up places his Pisa appointment in 1592, but that was the year of his move to Padua. The year 1609 is associated instead with his early telescopic observations, not his first university chair.