# Motion of mercury [duplicate]

I studied that mercury motion around the sun slightly displace by a certain value in each year. But, this is not predicted by kepler until general theory of relativity. What does general theory does with mercury.

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## marked as duplicate by Nathaniel, Jerry Schirmer, Waffle's Crazy Peanut, David Z♦Mar 26 '13 at 16:19

But this is a very special feature of the $A/r$ potential. If you consider the potential to be $A/r+B/r^2$, you would find out that the perihelion doesn't stay at the same place. General relativity basically allows you to replace the gravitational field of the Sun by the $A/r+B/r^2$ in a certain approximation; the extra term arises because the gravitational field is "nonlinear" and acts on itself i.e. Einstein's equations of general relativity don't quite obey the superposition principle. The second term $B/r^2$ is particularly important if $r$ is small enough, it's very strong for the planets that are closest to the Sun. Mercury is ideal to see it.