Published by Sir Isaac Newton in 1687, and sometimes also known as the Universal Law of Gravity, this was the first formulation of the idea that all bodies with mass pull on each other across space. Newton observed that the force of gravitybetween two objects is proportional to the product of the two masses, and inversely proportional to the square of the distance between them. Although the theory has since been superseded by Albert Einstein's General Theory of Relativity, it predicts the movements of the Sun, the Moon and the planets to a high degree of accuracy and it continues to be used as an excellent approximation of the effects of gravity for everyday applications (relativity is only required when there is a need for extreme precision, or when dealing with the gravitation of very massive objects).