The earth is an oblate spheroid, but so close that it has a moment of inertia about its spin axis roughly equal to 2/5 MR2. R is the radius of the earth. The gravitational system acting on the oblate spheroid (tilted away from the orbital plane of motion by 23.45 degrees) is equivalent to a force F and a couple M. The effect of the couple is to make the earth precess about a perpendicular to the orbital plane (precession of the equinoxes). Given that the time for a complete precession of the equinoxes is 25800 years.
Required:
Calculate the size of the couple (i.e the torque on the planet).