Galileo Galilei

Galileo Galilei turned the telescope into an instrument of proof, established the physics of falling bodies, and was condemned by the Roman Inquisition for defending Copernicus. Born in Pisa in 1564 to a musician and music theorist, he abandoned medical studies for mathematics and taught at Pisa and then Padua from 1592, supplementing a poor salary by selling instruments and casting horoscopes. Hearing of a Dutch spyglass in 1609, he built his own to about twenty times magnification and turned it upward. Sidereus Nuncius in 1610 reported mountains on the moon, that the Milky Way resolves into stars, and four satellites orbiting Jupiter — bodies plainly not circling the earth. He later observed the phases of Venus, which Ptolemy's system could not produce, and sunspots, which contradicted the incorruptibility of the heavens. His mechanics mattered as much. He established that bodies fall with equal acceleration regardless of weight, that projectiles follow parabolas, and that motion persists without a mover — the principle Newton took as his first law. The story of dropping weights from the Leaning Tower is likely apocryphal; the results came from rolling balls down inclined planes and timing them. Warned in 1616 not to hold or defend heliocentrism, he published the Dialogue Concerning the Two Chief World Systems in 1632 with papal permission, then put the Pope's own argument in the mouth of a character named Simplicio. Tried in 1633, he abjured under threat of torture and spent his remaining nine years under house arrest at Arcetri. There, blind by 1638, he completed the Two New Sciences, smuggled out and printed in Leiden. He died in 1642. The Church formally acknowledged the error in 1992.

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