>> I haven't been able to get a clarification to a vexing question >> concerning Mercury's perihelion precession-al orbit, specifically the >> angular direction such observations manifests as. For example, >> hypothetically speaking here, let's pretend we have a space ship and >> have stationed it approximately 90 million miles distant from the sun. >> Also, our spaceship is not within the ecliptic plane but positioned at >> one of the Sun's poles. Mercury is observed to be orbiting around the >> sun in a clock-wise pattern. Under such a scenario what would the >> angular direction of Mercury's perihelion precession manifest as? I >> -suspect- the perihelion PRE-cession of Mercury's orbit implies that >> the phenomenon would manifest in a counter-clockwise direction, but I >> haven't been able to get a clear answer to that one. >> >> Pardon my ignorance, on this matter. I'm wondering out loud, here: >> Does the term "PRE"cession mean: "in the opposite direction of..." as >> to the orbital direction? Mongo don't know. > > Neither. Precession can be either prograde or retrograde. Mercury's > perihelion precession is prograde, if I'm not mistaken.
I am. Mercury's perihelion advance is retrograde. It happens in the same direction than Earth's axial precession, which is retrograde. See the table called "Sources of the precession of perihelion for Mercury" in http://en.wikipedia.org/wiki/Tests_of_general_relativity All effects add up.
