Galileo Galilei (1564-1642)

Istoria e dimostrazioni intorno alle macchie solari, Rome, 1613
Florence, Biblioteca Nazionale Centrale, Post. 155, pp. 94-95

These letters announce his discovery of dark spots on the Sun's surface. Galileo used his observation of the sunspots to prove that the Sun rotates on its own axis. The work contains numerous engravings showing the positions of the sunspots.