Galileo began teaching at the University of Padua in 1592.
The move followed his appointment in 1589 to the chair of mathematics at the University of Pisa. After his father died in 1591, Galileo also faced greater family responsibilities, including helping support his younger brother. In 1592, he accepted a position at Padua, then part of the Republic of Venice, and remained there until 1610.
At Padua, Galileo taught geometry, mechanics, and astronomy. The university offered him a productive setting for both academic research and practical work. He designed and sold scientific instruments, studied motion, worked on fortifications and engineering, and developed a reputation as an energetic teacher who supplemented his university income with private instruction.
His Padua years also preceded his most famous telescopic discoveries. After improving the telescope in 1609, Galileo observed lunar features, the Milky Way, sunspots, the phases of Venus, and four moons orbiting Jupiter. Those observations strengthened the case against the traditional Earth-centered cosmos. Galileo left Padua for Florence in 1610 after accepting the patronage of Cosimo II de' Medici.