January 22, 1592 – October 24, 1655
Pierre Gassendi was a French philosopher, priest, scientist, astronomer, and mathematician. With a church position in south-east France, he also spent much time in Paris, where he was a leader of a group of free-thinking intellectuals.
He was also an active observational scientist. In 1631, Gassendi became the first person to observe the transit of a planet across the Sun, viewing the transit of Mercury that Kepler had predicted. He was then the first to publish data on the transit. In December of the same year, he watched for the transit of Venus, but this event occurred when it was night time in Paris.
He wrote numerous philosophical works, and some of the positions he worked out are considered significant, finding a way between scepticism and dogmatism. Richard Popkin indicates that Gassendi was one of the first thinkers to formulate the modern "scientific outlook", of moderated scepticism and empiricism. He clashed with his contemporary Descartes on the possibility of certain knowledge. His best known intellectual project attempted to reconcile Epicurean atomism with Christianity. (In natural philosophy, atomism is the theory that all the objects in the universe are composed of very small, indestructible building blocks – atoms.)
In 1653 he published works on the lives of Copernicus and of Tycho Brahe. The Lunar crater Gassendi is named after him.