# Dictionary

## perihelion advance, relativistic

For planetary orbits, there is a minute difference between the predictions of Newtonian gravity and general relativity. For instance, in Newton’s theory, the orbital curve of a lonely planet orbiting a star is an ellipse. In general relativity, it is a kind of rosetta curve, corresponding to a partial ellipse that, in toto, shifts a bit with each additional orbit. The shift can be defined by looking at the point on each orbit closest to the sun, each perihelion, and the additional relativistic shift is, hence, called relativistic perihelion shift or relativistic perihelion advance. A picture can be seen on the page A planet goes astray in the chapter General relativity of Elementary Einstein.