Nicolaus Copernicus (1473-1543) proposed that the Sun, not the Earth, was the centre of the Solar System. Such a model is called a heliocentric system. According to this new order, the Earth is just another planet, and the Moon is in orbit around the Earth, not the Sun. The stars are distant objects that do not revolve around the Sun. Instead, the Earth is assumed to rotate once in 24 hours, causing the stars to apparently revolve around the Earth in the opposite direction.