In 1632, after years of silence on the Copernican issue, Galileo published his Dialogo dei due massimi sistemi del mondo (Dialogue on Two Chief World Systems). The Inquisition summoned the aged author to Rome, where he was examined and threatened with torture. Galileo recanted and was sentenced to house arrest for the remainder of his life. As he rose from his knees after making a solem renunciation of the Copernican doctrine, he was heard to mutter, "Eppur si muove" (But still, it moves).

Although he is held by many as the hero of Science vs. Religion, it should be noted that Galileo was an EXTREMELY religious man. He was willing to give up all of his theories in the face of the Inquisition. However, when they asked him to sign a paper that said he had no faith and that he was disconnected from God, he refused. It should also be noted that he was sheltered by a member of the church, specifically a Cardinal and was encouraged to continue his studies along a different path. This information was taken from the book Galileo's Daughters, if anyone wants to know my source.

Galileo was born in Pisa in 1564. He studied at the University of Pisa, where he was appointed to the chair of mathematics in 1589. It was at this point that Galileo began to express criticisms of various parts of the Aristotelian natural philosophy being taught. His laws of falling bodies are the best known symbol of his dissatisfaction. Soon Galileo moved to the chair of mathematics at Padua, where he remained until 1610.

Galileo’s observations of and public lectures on the nova of 1604 first gave him a reputation as an astronomer. Until this point he had been known as a mathematician. In the absence of observable parallax, the nova indeed appeared to be a new star. Galileo lectured on the difficulties with the Aristotelian idea of the immutability of the heavens arising from this fact. In 1610 Galileo was appointed mathematician to the Grand Duke of Tuscany, and he returned to Florence.

Much of Galileo’s most important astronomical work dates from the 1610s. It was in the January of 1610 that Galileo first observed the four “Galilean” satellites of Jupiter. This was problematical for the anti-Copernicans, as it suggested there were centres of rotation in the Universe other than the Earth. A little more than a year later, Galileo was able to distinguish between the satellites, and hence determine their periods of revolution.

Before the end of 1610, Galileo had observed that Saturn appeared non-circular, although he could not resolve the rings, and thought them to be satellites revolving very close to the planet. Galileo’s observations of the phases of Venus posed severe problems for the Ptolemaic model of the Universe, which could not account for all of the observed phases.

Galileo also attempted to solve the infamous problem of determining longitude at sea (the eventual solution of this problem is described in the excellent Longitude by Dava Sobel – who is also the author of Galileo’s Daughter, I believe). He proposed the use of the Jovian satellites as a sort of Universal clock, by the use of a device he had designed, and tables of eclipses of the Satellites. He failed to collect the 25,000 florins prize offered by the Stadholder of the Netherlands for the solution of the Longitude problem.

In 1632 Galileo published the Dialogue Concerning the Two Chief World Systems, the Copernican and the Ptolemaic. This book was written as a series of discussions between three people: Salviati (representing Galileo); Sagredo (an intelligent listener); and Simplicio (a dull-witted Aristotelian). As the Dialogue was written in this popular style, it was much more widely accessible than previous books on Copernicanism had been, and so attracted the attention of the Holy Office. Galileo was summoned to Rome, where a tribunal of seven Cardinals required Galileo to solemnly abjure his theory, and sentenced him to house arrest in Arcetri. Galileo’s health deteriorated – by 1638 he was completely blind. He died on 8th January 1642.

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