A KEPLER’S NOTE ON SECULAR INEQUALITIES

Abstract

I discuss the problem of secular inequalities in Kepler by giving account of a manuscript note that has not been published until 1860. In his note Kepler points out the need for a model, clearly inspired by the method of epicycles, that describes the secular inequalities as periodic ones. I bring attention to this point, that seems to have been underestimated, since the references to Kepler’s work usually report only that he observed a decreasing mean motion for Saturn and an increasing one for Jupiter.