Galilei, Galileo

Galilei, Galileo (1564–1642), mathematician and scientist, usually known as ‘Galileo’. As professor of mathematics at Pisa and then Padua, he developed ideas on a new science of motion that can be seen as leading to Newtonian physics. In 1609 he heard of a new instrument (later known as the telescope) and embarked on a systematic observation of the heavens; he used the results in works published in 1610 and 1613 to support a heliocentric Copernican cosmology. In 1610 he moved to Florence. Soon the theological significance of Copernicanism for the first time became a matter of concern, and in 1616 the Holy Office asserted that to maintain the immobility and centrality of the sun as opposed to that of the earth was heretical. Apparently under the impression that he could then discuss the new system provided he treated it as hypothetical, Galileo published a new work on the subject in 1632. He was summoned before the Inquisition, made to recant, and spent the rest of his life under house arrest. In 1992 John Paul II endorsed the report of a commission admitting the ‘subjective error’ of Galileo's judges.