Abstract

Abstract: A part of central force between planetary and central bodies cause their spin motions. All bodies in planetary systems develop mean accelerating spin motion. Depending on their orbital parameters, planets and central bodies may spin in forward direction, rearward direction or, in rare cases, may have no spin motion at all. All bodies in a planetary system tend to spin in their common orbital plane. Angular accelerations of orbiting bodies continue indefinitely until their high spin speeds cause disintegration of planets and planetary system. In a planetary system, consistency of body-matter and radial size of a body determine relative spin speeds at different parts of its body. Equatorial region of all very large bodies spin faster than their polar region or regions towards their spin-axes. Lengthening of (terrestrial) solar days, presently misinterpreted as slowing down of earth?s spin motion, is the result of insufficient compensation to earth?s apparent spin motion about the sun.