I've been reading that the orbits of the Planets are precessing. i.e. the actual orbit moves round. This is along the line of apsides, which is the widest part of the elliptical orbit. So the line itself is moving anticlockwise.
Anyway Newtons universal Gravitation in no way predicts this but the as the other planets move round the Sun in an anticlockwise direction they pull each others orbits round. Mercury's precession was greater than expected, which was corrected by Einstein.
Anyway, Lagrange proposed that the influence of other planets would cause precession but would not lengthen or shorten an orbit. And the planets were made into rings (to average things out) i.e. the orbital path was seen as a ring. This is known as perturbation theory. Perturbation theory was also used when (the Church) it was thought everything went round the Earth. In other words as stated on wikipedia:
Perturbation theory comprises mathematical methods that are used to find an approximate solution to a problem which cannot be solved exactly, by starting from the exact solution of a related problem.
So my point is, As we don't know how the Planets orbits came about (although we presume the solar system condensed out of a cloud), we cannot be confident about why they are precessing. In other words as we don't know their origin we don't know whether they would be precessing anyway. Just wondering if anyone else feels this presumption (and perturbation theory) may be unwise or erroneous