# Precession of Mercury and period of rotation

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1. Apr 15, 2015

### vinven7

HI - we know that the orbit of mercury precesses (I hope I am using the right terminology here). Which basically means that the orbit seems to undergo some sort of rotation in the ecliptic plane. Does this also mean that the period of Mercury's orbit as seen from the earth is not uniform but changes with each orbit? (Please let me know if this question is clear enough, perhaps Im not expressing it well enough)

2. Apr 15, 2015

### SteamKing

Staff Emeritus
I don't know about the period of Mercury's orbit, but the perihelion, the point at which Mercury is closest to the sun, is what precesses, or moves around the sun over time:

http://physics.ucr.edu/~wudka/Physics7/Notes_www/node98.html

The orbits of all the planets in the solar system precess to some degree, but Mercury's is the one which caused the most problems. The amount of precession observed differed slightly from what was predicted using Newton's laws of motion, by an amount 43 arc seconds per century. Many attempts at resolving this discrepancy using Newtonian physics alone failed, but Einstein was able to show, using his general theory of relativity, how much the orbit of Mercury should precess.

http://en.wikipedia.org/wiki/General_relativity

http://en.wikipedia.org/wiki/Tests_of_general_relativity