Wikipedia: Galileo Galilei

Scientific achievements

Galileo, though likely not the first person to use a telescope to observe the sky, did more than anyone to popularize the device and can be fairly called the father of modern astronomy. Galileo discovered the four largest satellites of Jupiter, and he was the first westerner to observe sunspots (there is an indication that chinese astronomers had already observed them).

His experimental work in dynamics paved the way for Isaac Newton's laws of motion, and he is often credited with being one of the first scientists to fully exploit the experimental method and to insist on a mathematical description of the laws of nature. His study of balls rolling down inclined planes convinced him that falling objects are accelerated independent of their mass, and that objects retain their velocity unless a force acts on them.

Many of Galileo's theories exist today only in his notes and drawings. He created sketches of imaginary devices such as a candle and mirror combination to reflect light through an entire home, an automatic tomato picker, a pocket comb that doubled as an eating utensil, and what appeared to be a crude form of ballpoint pen.

Church Controversy

A devout Catholic, his writings on the Copernican (incorporating a heliocentric, or sun-centered solar system) model of the universe disturbed the church. The Church, and most everyone else, held to a Ptolemaic, or Aristotelian view, incorporating an Earth-centered theory of the universe.

Despite his continued insistence that his work in the area was purely theoretical, and despite his close friendship with Maffeo Barberini who later became Pope Urban VIII and presided throughout the ordeal, Galileo was forced to recant and was put under life-long house arrest (1633-1642). Galileo's Dialogue was banned. That the risk Galileo was facing was a real one had been proven by the church in the earlier trial against Giordano Bruno, who was burned at the stake in 1600 for holding a naturalistic view of the universe.

Galileo is a classic case of a scholar forced to recant a scientific insight because it offended powerful, conservative forces in society: for the church at the time, it was not the scientific method that should be used to find truth -- especially in certain areas -- but the doctrine as interpreted and defined by church scholars, and this doctrine was defended with torture, murder, deprivation of freedom, and censorship.

In 1992, 359 years after the Galileo trial, Pope John Paul II issued an apology, lifting the edict of Inquisition against Galileo: "Galileo sensed in his scientific research the presence of the Creator who, stirring in the depths of his spirit, stimulated him, anticipating and assisting his intuitions."