Galileo and the Mathematization of Nature

Galileo Galilei (1564–1642), born in Pisa and later professor of mathematics at Pisa and then Padua before becoming chief mathematician and philosopher to the Grand Duke of Tuscany in 1610, transformed astronomy through his telescopic observations, published that same year in the short but sensational treatise Sidereus Nuncius ("Starry Messenger"). Using an instrument he built himself, an improvement on the Dutch spyglass first reported in 1608, Galileo reported mountains and craters on the Moon's surface, which contradicted the Aristotelian doctrine that celestial bodies were perfectly smooth and unchanging; countless previously invisible fixed stars, showing the Milky Way to be composed of a vast multitude of individual stars; and four moons orbiting Jupiter, which he named the "Medicean Stars" in honor of his patrons the Medici — bodies whose evident orbit around a body other than the Earth directly undercut the geocentric assumption that all heavenly motion must center on a single point, the Earth. Galileo's subsequent observation of the full range of phases of Venus, reported in 1610–1611, provided a further, especially decisive piece of evidence: the phases Venus actually exhibits are compatible with the Copernican and Tychonic systems, in which Venus orbits the Sun, but not with the traditional Ptolemaic geocentric arrangement, which predicts Venus could show only a limited crescent phase.