Galileo Galilei

In 1609, Galileo Galilei heard rumors of a Dutch spyglass and built his own, turning it toward the sky. What he saw changed everything: the Moon had mountains, Jupiter had moons, Venus showed phases that could only exist if it orbited the Sun. These simple observations demolished the ancient Aristotelian cosmos where Earth sat motionless at the center of crystalline spheres. Galileo published his findings, debated furiously, and wrote in Italian rather than Latin so ordinary people could read the truth. He also rolled balls down inclined planes, dropped weights, and demonstrated that mathematics could describe motion with precision no philosopher had achieved. The Church eventually tried him for heresy, forced him to recant, and confined him to house arrest for the rest of his life. Legend says he muttered 'And yet it moves' as he knelt. Whether or not he spoke those words, his work proved them true.