Galileo affair

Between 1610 and 1633 the Italian astronomer Galileo Galilei clashed with the Catholic Church over his support for the idea that the Earth moves around the Sun. The dispute passed through two formal stages: a ruling by the Roman Inquisition in 1616 that condemned the Sun-centred model, and a trial in 1633 that left Galileo under house arrest for the rest of his life. It became one of the most debated episodes in the relationship between science and religion.

Galileo turned a telescope on the sky in late 1609 and in March 1610 published The Starry Messenger. He described mountains on the Moon, smaller bodies orbiting Jupiter, and faint stars hidden within what had looked like cloudy patches. He went on to observe sunspots and the phases of Venus. These findings fitted poorly with the Earth-centred system of Ptolemy and Aristotle and lent support to the heliocentric model that Nicolaus Copernicus had published in 1543. Jesuit astronomers in Rome soon confirmed many of the observations, although the hybrid, still Earth-centred system of Tycho Brahe, in which Venus for example circled the Sun, offered a way to accept them without a moving Earth.

Opponents argued that a moving Earth contradicted passages of the Bible. Galileo set out his view of how Scripture should be read on natural questions in a letter to his former pupil Benedetto Castelli, later expanded in 1615 as the Letter to the Grand Duchess Christina. Late in 1614 the Dominican friar Tommaso Caccini attacked him from a Florentine pulpit, and in February 1615 another Dominican, Niccolò Lorini, sent the Castelli letter to the Inquisition. Cardinal Robert Bellarmine, the leading theologian involved, advised that Copernicanism could be discussed as a calculating hypothesis but not presented as physical truth unless conclusively proved.

On 24 February 1616 a panel of theological advisers declared the proposition of a stationary Sun "formally heretical" and that of a moving Earth at least erroneous in faith. Two days later, on the instructions of Pope Paul V, Bellarmine told Galileo to abandon the opinion. On 5 March the Congregation of the Index banned books advocating the Copernican system and suspended Copernicus's own work until it was corrected; an amended version was later permitted.

When Urban VIII became pope in 1623, Galileo found a more sympathetic patron, who allowed him to write about Copernicanism provided he treated it as a hypothesis. The resulting Dialogue Concerning the Two Chief World Systems appeared in 1632. Its defender of the old view, Simplicio, was portrayed as a fool, and the pope's own arguments were placed in his mouth, which gave great offence. The book's sale was halted and Galileo was summoned to Rome. Interrogated under the threat of torture, he was found "vehemently suspect of heresy" on 22 June 1633, made to abjure his views, and sentenced to imprisonment, commuted the next day to house arrest. The Dialogue was banned.

According to a popular legend, Galileo muttered "Eppur si muove" ("and yet it moves") after recanting, but no evidence shows that he said it, and the story first appears about a century after his death.

Galileo spent his final years at his villa at Arcetri, outside Florence, where he continued work on mechanics and published a further scientific book in Holland in 1638. The Church dropped its general ban on heliocentric books from the Index in 1758, and the Dialogue and Copernicus's book were left out of the 1835 edition. In 1979 Pope John Paul II called for the case to be re-examined; a commission set up in 1981 reported without a definitive result, and in 1992 the pope acknowledged that the theologians of Galileo's day had erred.

Our 1600 and 1650 maps show Italy in this period, including the Papal States, whose capital, Rome, was the seat of the Inquisition that tried Galileo.