Lagrangian planetary equations in Schwarzschild space--time
  We have developed a method to study the effects of a perturbation to the motion of a test point--like object in a Schwarzschild spacetime. Such a method is the extension of the Lagrangian planetary equations of classical celestial mechanics into the framework of the full theory of general relativity. The method provides a natural approach to account for relativistic effects in the unperturbed problem in an exact way. 
Mirco Calura, Enrico Montanari and Pierluigi Fortini (University of   Ferrara and INFN sezione di Ferrara, Italy)