From Nick Greene,
Your Guide to Space / Astronomy.
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Early in 1616, Copernican books were subjected to censorship by edict, and the Jesuit cardinal Robert Bellarmine instructed Galileo that he must no longer hold or defend the concept that the earth moves. Cardinal Bellarmine had previously advised him to treat this subject only hypothetically and for scientific purposes, without taking Copernican concepts as literally true or attempting to reconcile them with the Bible. Galileo remained silent on the subject for years, working on a method of determining longitudes at sea by using his predictions of the positions of Jupiter's satellites, resuming his earlier studies of falling bodies, and setting forth his views on scientific reasoning in a book on comets, The Assayer (1623; trans. 1957).

In 1630, Galileo received license from Catholic censors to publish a book called Dialogue on the Tides, which discussed both the Ptolemaic and Copernican theories, though they changed the title to Dialogue on Two Chief World Systems. It was published in 1632.

Despite holding two licenses for the book, he was summoned to Rome by the Inquisition to stand trial for "grave suspicion of heresy," stating that he had been ordered personally in 1616 to not discuss Copernicanism, either orally or written. Despite the fact that Galileo was able to produce a certificate signed by the late cardinal Bellarmine stating that he was under no further restrictions than applied to other Catholics, he was compelled in 1633 to abjure and was sentenced to life in prison.

That sentence was swiftly commuted to permanent house arrest, but the Dialogue was ordered to be burned, and the sentence against him was to be read publicly in every university. His final book, Discourses Concerning Two New Sciences was published at Leiden in 1638. Discussing and refining his earlier studies of motion and principles of mechanics, it opened a road that was to lead Newton to his law of universal gravitation that linked Kepler's planetary laws with Galileo's mathematical physics. Galileo lost his eyesight before it was published. He died at Arcetri, near Florence, on January 8, 1642.

An investigation into the astronomer's condemnation, calling for its reversal, was opened in 1979 by Pope John Paul II. In October 1992 a papal commission acknowledged the Vatican had made errors, but stopped short of admitting the Church was wrong to convict Galileo on a charge of heresy because of his belief that the Earth rotates round the sun.

Other Resources

• Galileo Galilei Quotations
• Review: "Galileo's Daughter" by Dava Sobel
• Video: "Galileo and the Leaning Tower of Pisa"