Precession of Mercury's perihelion

Precession of Mercury

Fig. 6.19 . Instead of always tracing out the same ellipse, the orbit of Mercury pivots around the focus occupied by the Sun. The point of closest approach to the Sun, the perihelion, is slowly rotating ahead of the point predicted by Newton's theory of gravitation. This was at first explained by the gravitational tug of an unknown planet called Vulcan thought to be revolving about the Sun inside Mercury’s orbit, but we now know that Vulcan does not exist. Mercury's anomalous motion was eventually explained by Einstein's new theory of gravity in which the Sun's curvature of space makes the planet move in a slowly revolving ellipse.

Copyright 2010, Professor Kenneth R. Lang, Tufts University