Proving that the Earth orbits the Sun
Learning about the Solar System
In 1600, a man was burned alive by order of the Inquisition for the heretical suggestion that the Earth moved around the Sun. Thirty-four years later, charged with the same crime, 68-year-old Galileo Galilei knelt before ten cardinals, judges of the Inquisition.
Galileo looked down at his hands, twisted with arthritis. The choice was plain: recant or face torture and death. That afternoon he told his judges, "I do not consider the view of Copernicus as true and have never considered it as true," and so saved himself from execution.
The course of events that was to lead to Galileo's confrontation with the awesome powers of the Inquisition began in 1609 on a visit to Venice. Friends told him about the invention of a Dutchman, Hans Lippershey, which could make distant objects seem close - a telescope. At once, Galileo set about grinding glass into lenses. After many tries he made a telescope that magnified 30 times. In January 1610, Galileo pointed his telescope at the night sky and began to look at the heavens.
His startling observations seemed to demolish objections to the theories of the Polish astronomer Copernicus that the Earth and planets moved around the Sun. The Church held the view that the Earth could not move in space because it would leave its Moon behind. Yet Galileo discovered no fewer that four moons around Jupiter, which clearly moved across the sky.
Another argument against Copernicus's theory was that Venus did not appear to have phases, like the Moon, and that if Venus were orbiting the Sun, it's reflection ofthe Sun's light would have appeared in phases as it moved. Galileo found that, seen through a telescope, Venus did have phases.
In 1624, Galileo asked Pope Urban VIII for permission to publish support for Copernicus's view of the structure of the Universe. Urban agreed to allow Galileo to write a book that put forward the Copernican view, provided the Church's official view, based on the work of the 4th-century astronomer Ptolemy, was given equal prominence.
Galileo's book, Dialogue Concerning the Two Chief World Systems - Ptolemaic and Copernican, was published in February 1632. By August the Pope realised that the argument in the Dialogue was biased against the Church. The Copernican used clever reasoning, while the follower of Ptolemy presented feeble arguments.
Forced to recant
In October 1633, Galileo was summoned to Rome to face the Inqusition. There, the cardinals cross-examined him over a period of ten months, but they did not resort to torture. Initially, he put forward a strong defence of his views, but eventually he said his book was wrong. In 1634, the Dialogue was banned and Galileo returned to his villa in the hills above Florence, where he spent the last eight years of his life under house arrest.