His telescope found Jupiter's moons — and put him on trial for how the universe works.
Galileo Galilei (1564–1642) was the Italian astronomer and physicist whose telescopic discoveries — the moons of Jupiter, the phases of Venus, the mountains of the Moon — proved that the Earth moves around the Sun, and whose 1633 trial by the Inquisition made him the enduring symbol of science against dogma.
A professor at Pisa and Padua, he improved the telescope to twentyfold magnification and, in 1610, published the 'Starry Messenger', announcing a universe no one had seen. His later work on motion laid the foundations of modern physics.
Hearing in 1609 of a Dutch spyglass, Galileo built his own and rapidly improved it, grinding better lenses until he reached about twenty times magnification. Turned skyward, it revealed what the naked eye could never see: mountains and craters on the Moon, the phases of Venus — which only make sense if Venus orbits the Sun — and four bright points circling Jupiter.
Those four moons, published in the 'Sidereus Nuncius' of March 1610, were decisive: here was a miniature system in which bodies plainly orbited something other than the Earth. He named them the Medicean stars after his patrons, the Medici of Florence, who made him their court mathematician.
Galileo championed the Copernican system — the Sun at the center, the Earth in motion — in Italian, for the public, not in scholarly Latin. His 'Dialogue Concerning the Two Chief World Systems' of 1632 put the Church's position in the mouth of a character named Simplicio, the simpleton.
Summoned to Rome in 1633, the 69-year-old was tried by the Inquisition, forced to abjure the Earth's motion, and sentenced to house arrest for life. He spent his last nine years at Arcetri, blind but still working.
Under house arrest he wrote his greatest scientific work, the 'Discourses and Mathematical Demonstrations Relating to Two New Sciences' (1638): the law of falling bodies — that all objects fall at the same rate regardless of weight, tested on inclined planes — the parabolic path of projectiles, and the principle of inertia.
Newton would build his mechanics on Galileo's foundations. The telescope, the moons of Jupiter, the trial: together they made him, in Einstein's phrase, the father of modern science — honored, centuries later, by the Church that condemned him.
