BEFORE Galileo’s time, many people believed that the sun, the planets, and the stars all revolved around the earth. That belief was part of the official dogma of the Catholic Church.

With his telescope, however, Galileo saw evidence that contradicted widely accepted scientific teachings. For example, as he watched sunspots appear to shift across the surface of the sun, he discerned that the sun rotates on an axis. Observations like this greatly increased man’s knowledge of the universe, yet they would also result in Galileo’s coming into direct conflict with the Catholic Church.

Decades earlier, the Polish astronomer Nicolaus Copernicus developed a theory that the earth moves around the sun. Galileo studied Copernicus’ work on the movements of celestial bodies and collected evidence in harmony with the theory. Initially, Galileo hesitated to publicize some of his observations, fearing that they would be met with ridicule and scorn.  Unable to restrain his enthusiasm for what he saw through his telescope, he eventually went public with his discoveries. Some scientists found his arguments to be provocative, and soon clergymen were discrediting Galileo from their pulpits.

In 1616, Cardinal Bellarmine, “a leading theologian of the period,” informed Galileo of a newly issued Catholic decree against Copernicus’ ideas. He strongly urged Galileo to comply with that decree, and for years thereafter Galileo did not argue publicly that the earth moves around the sun.

In 1623, Pope Urban VIII, Galileo’s friend, began to reign. So in 1624, Galileo asked the pope to revoke the 1616 decree. Instead, Urban urged Galileo to explain the conflicting theories of Copernicus and Aristotle in a way that favored neither.

Galileo then wrote a book entitled Dialogue on the Great World Systems. Although the pope had ordered Galileo to be neutral, the book came across as favoring Copernicus’ conclusions. Soon Galileo’s enemies were claiming that his book ridiculed the pope. Accused of heresy and threatened with torture, Galileo was forced to deny the teachings of Copernicus. In 1633, the Roman Inquisition sentenced him to perpetual house arrest and banned his writings. Galileo died at home in Arcetri, near Florence, on January 8, 1642.

For hundreds of years, some of Galileo’s works remained on the index of books that Catholics were not permitted to read. But in 1979, the church reconsidered the action taken by the Roman Inquisition 300 years earlier. Finally, in 1992, Pope John Paul II acknowledged that the Catholic Church had wrongly condemned Galileo.