Galileo addresses an elaborate introduction to his patron, Cosimo II de’ Medici, on the nature of human fame. In Galileo’s view, we build monuments to great men to preserve their achievements, but we ought instead to look beyond mere earthly realms to the heavens. Galileo even decides to name Jupiter’s suns—which he recently discovered—the Medicean stars after Cosimo. He hopes that these stars will immortalize Cosimo’s strengths and virtues.

Via a “new spyglass” (the newly invented telescope), Galileo was able to view the surface of the moon magnified to 900 times larger than it appears to the naked eye. In doing so, Galileo discovered that the moon’s surface is not smooth and polished, as previously thought, but rough and uneven and “covered everywhere, just like the earth’s surface, with huge prominences, deep valleys, and chasms” (28). In addition, the telescope enabled Galileo to view the Milky Way more accurately than ever before, and—a discovery which “surpasses all wonders by far” (28)—to discover four “wandering stars” attached to Jupiter. Galileo hopes that the telescope will aid in the discovery of “still more remarkable” (28) things in the future.

Galileo next explains how he came by the telescope and describes its nature and construction.