"Eppur si muove" (And yet it moves)
Galileo Galilei's improvements to telescope design had allowed him to observe Jupiter’s four largest moons, now known in his honour as the Galilean moons. Such an observation caused a revolution in astronomy as it directly challenged the established belief that all heavenly bodies circled the Earth.
Galileo then observed the full phases of Venus. Something only possible if the planets were orbiting the Sun and not the Earth. This persuaded Galileo that the Copernican model was correct and the solar system was heliocentric.
In 1615 he was investigated by the Roman Inquisition, which concluded that his work was contrary to Holy Scripture. Galileo was ordered to abandon his support of heliocentrism by Pope Paul V.
17 years later, under the new pope, Urban VIII, Galileo published his book ‘Dialogue Concerning the Two Chief World Systems’, in which he championed Copernican theory. The book took the form of a discussion between two men, each advocating different models for the solar system. Unfortunately for Galileo he had named the geocentric supporter Simplico, which has connotations of him being a simpleton. The pope took this as a personal insult and in February 1633 Galileo was accused of heresy.
Despite defending himself vigourously, he was convicted and sentenced to life imprisonment by the Holy Office. This was later reduced to permanent house arrest after he withdrew his support for the Copernican model.
It is said that, after being forced to delcare that the Earth was the centre of the universe, Galileo muttered under his breath “Eppur si muove” (and yet it moves), but there is no contemporary evidence for what would have been a very dangerous act of defiance.