Overview: When Polish priest and astronomer Nicolaus Copernicus developed his extraordinary theory of a sun-centred universe 500 years ago, he was flying in the face of both science and religion. Mankind had believed for thousands of years that the earth was at the centre of the cosmos, and to disagree was to risk derision and accusations of heresy. For decades he was too afraid to publish, but the arrival of a young German scientist gave Copernicus courage, and his book and its extraordinary diagram were published in 1543, when he was on his deathbed. His image of the heliocentric universe changed forever our understanding of the Cosmos, and of our place in it.