Galileo showing the Doge of Venice how to use a telescope.

Galileo Galilei (15 Feb. 1564 8 Jan. 1642) was an Italian physicist, mathematician, philosopher and astronomer who played a pivotal role in establishing modern science at a time when contradiction of religion was considered heresy. It was as an astronomer that he was most controversial. Galileo developed telescopes that confirmed the phases of Venus, and the discovery of the four largest satellites of Jupiter (named the Galilean moons in his honour), as well as sunspots. In 1610, while a majority of philosophers and astronomers still subscribed to the geocentric opinion that the Earth was the centre of the universe, Galileo came out in support of Copernicus' heliocentric view that the Sun was at the center of the solar system. Galileo's opinions were met with outrage and bitter opposition, and he was denounced to the Roman Inquisition. In February 1616, although he had been cleared of any offence, the Catholic Church nevertheless condemned heliocentrism as 'false and contrary to [Christian] Scripture' and forced Galileo to renounce his scientific conclusions. However, in 1632, Galileo published 'Dialogue Concerning the Two Chief World Systems', in which he again defended heliocentrism. He was tried by the Inquisition, found 'vehemently suspect of heresy', forced to recant, and spent the rest of his life under house arrest. (Photo by: Pictures From History/Universal Images Group via Getty Images)