From Kepler's second law as well as conservation of angular momentum, we know that earth (any many other celestial objects) move faster when they get near the sun during their orbit and get slower when they are far away. This is a "change" in the angular speed so the derivative of it is a constant(if it's not a function). But this change must bring an angular acceleration α which in return brings us a torque due to the fact that Torque= I x α = r x F What is this force and where does it come from? Sun's gravity is a central force and can act only parallel to the displacement vector from sun-to-earth thus it can't have any torque effect at all. What force cause this acceleration of earth during these phases?