Nicolaus Copernicus (1473-1543 CE) was a Polish astronomer who famously proposed that the Earth and other planets revolved around the Sun in a heliocentric system and not, as then widely thought, in a geocentric system where the Earth is the centre. This was not a new idea as several earlier scholars had proposed a heliocentric system, but Copernicus additionally theorised a new order for the planets in terms of their distance from the Sun, that the Earth orbits the Sun once every year, and that the Earth turns entirely on its own axis each day. These ideas were contrary to those of the Catholic Church which considered humanity and the Earth as the proper and actual centre of God's universe. The reaction to Copernicus' major work, De Revolutionibus Orbium Coelestium (On the Revolutions of the Heavenly Spheres), published in the year he died, was muted, and there was hardly a revolutionary overturning of how everyone saw the world's place in the universe, as is often claimed. Nevertheless, the astronomer's work would slowly lead to further investigations by later scientists and mathematicians who eventually proved that Copernicus' heliocentric system with a spinning Earth, although containing flaws, was essentially correct.

To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge.

-Nicolaus Copernicus