Central forces and secular perihelion motion

The first-order orbital equation and its perturbed version under the form of an integro-differential equation provide a new method to study, respectively, the elliptical orbit and the secular motion of a planetary perihelion due to the perturbing action of an important category of central forces: the inverse-power radial forces. For this, a general formula is found. The related problems of the gravitational bending of fast particles and light rays are studied using the same methods. PACS Nos.: 02.60.Nm, 04.25.–g, 46.15.Ff, 45.50.Pk