planets, when the starting position was known. The Newtonian system was confirmed when Uranus was found not to be behaving in accordance with the Newtonian system which lead to the discovery of Neptune. The telescope had lead to the discovery of Uranus, in 1781 by William Herscel, the first planet discovered since ancient times. Observations of Uranus made it clear the planet was not behaving in the way predicted by Newton's laws. Calculations were made independently by both Urbain Leverrier and John Adams that suggested the gravitational effect of another planet could explain the behavior of Uranus. This lead to the discovery of Neptune in 1846, exactly where the calculations predicted. When the gravitational force of Neptune was taken into account the whole solar system corresponded exactly to Newton's theory. In the 19th century the development of spectroscopy which enables the identification of elements from the light they reflect revealed that the Sun had the same chemical make up as the stars and that the Sun was just another star. It only appears to be different to people due to the Sun being so much closer to us than the other stars. Newton's system had been well established for several hundred years when it was discovered, with new and more accurate measurements that the planet Mercury did not move in accordance with Newton's calculations. In 1905 Einstein published his special theory of relativity which described the universe but did not involve gravity. It dealt mainly with light and how the