A normal form theory for non--quasi--periodic systems is combined with the
special properties of the partially averaged Newtonian potential pointed out in
[15] to prove, in the averaged, planar three--body problem, the existence of a
plenty of motions where, periodically, the perihelion of the inner body affords
librations about one equilibrium position and its ellipse squeezes to a segment
before reversing its direction and again decreasing its eccentricity
(perihelion librations).Comment: 3 Figures, 30 page
