  The geodesic equations resulting from the Schwarzschild gravitational metric
element are solved exactly including the contribution from the Cosmological
constant. The exact solution is given by genus 2 Siegelsche modular forms. For
zero cosmological constant the hyperelliptic curve degenerates into an elliptic
curve and the resulting geodesic is solved by the Weierstra$\ss$ Jacobi modular
form. The solution is applied to the precise calculation of the perihelion
precession of the orbit of planet Mercury around the Sun.
