| Table of Contents: Introduction Classical Observations of Mercury The Planet Vulcan Einstein and Relativity Further Applications of Relativity Bibliography |
 Image source:http://theconversation.com/rippling-space-time-how-to-catch-einsteins-gravitational-waves-7058 The explanation for the oddities in the orbit of the planet Mercury was finally found in Albert Einstein's 1915 General Theory of Relativity. Einstein proposed that gravity was a result of the way that mass curves space, and it was not long before that understanding was being used to analyze previously confusing things in orbital mechanics. Mercury's perihelion was off from each previous measurement by a tiny fraction of a percent. A small deviation, but a consistent one. The English astronomer Arthur Eddington encouraged Einstein to apply his equations for General Relativity and find a prediction of how Mercury should move in his system. Einstein found that Mercury should have a precession of 43 arc-seconds, exactly as it is observed to. By Newtonian mechanics a planet's orbit around the Sun is a perfect ellipse with the Sun at one of the foci. This ellipse is described by the equation The understanding in General Relativity is that the orbit is slightly off from a self-contained ellipse. After completing each orbit the curved space near the Sun causes the perihelion direction to precess by a tiny amount (approximately 20 miles per orbit for Mercury). That is, the planet returns to rm but at a slightly different ϕ. The orbit then is where |