Galileo's telescopes: Facing the facts

Few events in history have proved as momentous as Galileo's discovery of the moons of Jupiter. David Wootton explains why.

An astronomer observes the sky in an engraving by Johannes Hevelius (1611-87). AKG Images.Four hundred years ago Galileo Galilei (1564-1642) was in a state of anxiety. In January he had discovered four moons orbiting Jupiter. In March he had published this and other remarkable discoveries made with his improved telescope in Sidereus Nuncius (‘The Starry Messenger’). But by the summer he was becoming profoundly alarmed. He had offered philosophers and mathematicians in Venice, Padua, Florence, Pisa and Bologna the chance to look through his telescope and confirm his discoveries. Some, including Cremonini, the highest paid academic in Italy and a good friend of Galileo’s, had simply refused. Others had looked, but had said they could not see what on earth he was talking about. Only Kepler in Germany had come out in his support, but he had yet to get hold of a decent telescope so had not seen the moons for himself. He was prepared to believe Galileo because he – and hardly anyone else – shared Galileo’s Copernicanism.

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