In this talk we shall discuss the Cartan geometry of the rotating Kepler problem. The rotating Kepler problem appears as the limit of the restricted planar three-body body when one of the masses goes to zero. As such, this problem plays the role of a simple approximation. We shall discuss the Cartan curvature and some of its relations with indices in the three-body problem. This is joint work with Kai Cieliebak and Urs Frauenfelder.