The Polish astronomer Nicolaus Copernicus (1473 - 1543) publishes De revolutionibus orbium coelestium, which changes perception of the universe by arguing that the Sun rather than the Earth is at the center of the Universe. Copernicus was upset by the implications of his own theory and worried about how the Church and the public would receive it, so he waited until his dying days to publish his book. Reactions were mixed and it took centuries for most people to accept his theory.