Galileo biography

Galileo began to express openly his support of the Copernican theory that the earth and planets revolved around the sun. This challenged the doctrine of Aristotle and the established order set by the Catholic Church.

In July 1609, Galileo learned about a simple telescope built by Dutch eyeglass makers, and he soon developed one of his own. In August, he demonstrated it to some Venetian merchants,

who saw its value for spotting ships and gave Galileo salary to manufacture several of them. However, Galileo’s ambition pushed him to go further, and in the fall of 1609 he made the fateful decision to turn his telescope toward the heavens. In March 1610, he published a small booklet, The Starry Messenger, revealing his discoveries that the moon was not flat and smooth, but a sphere with mountains and craters. He found Venus had phases like the moon, proving it rotated around the sun. He also discovered Jupiter had revolving moons, which didn’t revolve around the earth.

Soon Galileo began mounting a body of evidence that supported Copernican theory and contradicted Aristotle and Church doctrine. In 1612, he published his Discourse on Bodies in Water, refuting the Aristotelian explanation of why objects float in water, saying that it wasn’t because of their flat shape, but instead the weight of the object in relation to the water it displaced. In 1613, he published his observations of sunspots, which further refuted Aristotelian doctrine that the sun was perfect. That same year, Galileo wrote a letter to a student to explain how Copernican theory did not contradict Biblical passages, stating that scripture was written from an earthly perspective and implied that science provided a different, more accurate perspective. The letter was made public and Church Inquisition consultants pronounced Copernican theory heretical. In 1616, Galileo was ordered not to “hold, teach, or defend in any manner” the Copernican theory regarding the motion of the earth. Galileo obeyed the order for seven years, partly to make life easier and partly because he was a devoted Catholic.

In 1623, a friend of Galileo, Cardinal Maffeo Barberini, was selected as Pope Urban VIII. He allowed Galileo to pursue his work on astronomy and even encouraged him to publish it, on condition it be objective and not advocate Copernican theory. In 1632, Galileo published the Dialogue Concerning the Two Chief World Systems, a discussion among three people: one who supports Copernicus' heliocentric theory of the universe, one who argues against it, and one who is impartial. Though Galileo claimed Dialogues was neutral, it was clearly not. The advocate of Aristotelian belief comes across as the simpleton, getting caught in his own arguments.

Reaction by the Church

Church reaction against the book was swift, and Galileo was summoned to Rome. The Inquisition proceedings lasted from September 1632 to July 1633. During most of this time, Galileo was treated with respect and never imprisoned. However, in a final attempt to break him, Galileo was threatened with torture, and he finally admitted he had supported Copernican theory, but privately held that his statements were correct.