<Li> Newton's Theory does not fully explain the precession of the perihelion of the orbits of the planets, especially of planet Mercury, which was detected long after the life of Newton . There is a 43 arcsecond per century discrepancy between the Newtonian calculation, which arises only from the gravitational attractions from the other planets, and the observed precession, made with advanced telescopes during the 19th century . </Li> <Li> The predicted angular deflection of light rays by gravity that is calculated by using Newton's Theory is only one - half of the deflection that is actually observed by astronomers . Calculations using General Relativity are in much closer agreement with the astronomical observations . </Li> <Li> In spiral galaxies, the orbiting of stars around their centers seems to strongly disobey Newton's law of universal gravitation . Astrophysicists, however, explain this spectacular phenomenon in the framework of Newton's laws, with the presence of large amounts of dark matter . </Li> <P> While Newton was able to formulate his law of gravity in his monumental work, he was deeply uncomfortable with the notion of "action at a distance" that his equations implied . In 1692, in his third letter to Bentley, he wrote: "That one body may act upon another at a distance through a vacuum without the mediation of anything else, by and through which their action and force may be conveyed from one another, is to me so great an absurdity that, I believe, no man who has in philosophic matters a competent faculty of thinking could ever fall into it ." </P>

In the space below write the equation for the law of universal gravitation