Galileo Galilei was born in Pisa in 1564, the first of six children of Vincenzo Galilei, a musician and scholar. In 1581 he entered the University of Pisa to study medicine, but was soon sidetracked by mathematics. In 1583 he made his first important discovery, describing the rules that govern the motion of pendulums. From 1589 to 1610, Galileo was chair of mathematics at the universities of Pisa and then Padua. During those years he performed the experiments with falling bodies that made his most significant contribution to physics.
In 1609 Galileo built his first telescope, improving upon a Dutch design. In January of 1610 he discovered four new “stars” orbiting Jupiter—the planet’s four largest moons. He quickly published a short treatise outlining his discoveries, “Siderius Nuncius” (“The Starry Messenger”), which also contained observations of the moon’s surface and descriptions of a multitude of new stars in the Milky Way. “The Starry Messenger” made Galileo a celebrity in Italy. Cosimo II appointed him mathematician and philosopher to the Medicis, offering him a platform for proclaiming his theories and ridiculing his opponents.
In 1616 the Catholic Church placed Nicholas Copernicus’ “De Revolutionibus,” the first modern scientific argument for a heliocentric (sun-centered) universe, on its index of banned books. Pope Paul V summoned Galileo to Rome and told him he could no longer support Copernicus publicly.In 1632 Galileo published his “Dialogue Concerning the Two Chief World Systems,” which supposedly presented arguments for both sides of the heliocentrism debate. His attempt at balance fooled no one, and it especially didn’t help that his advocate for geocentrism was named “Simplicius.”
Galileo’s motion experiments paved the way for the codification of classical mechanics by Isaac Newton. His heliocentrism (with modifications by Kepler) soon became accepted scientific fact. His inventions, from compasses and balances to improved telescopes and microscopes, revolutionized astronomy and biology. And his penchant for thoughtful and inventive experimentation pushed the scientific method toward its modern form.