  The Old Quantum Mechanics actions discretization rules for periodic motions
on the atomic scale (Bohr-Sommerfeld) have been suitably modified in order to
account the gravitational field instead of the electrostatic one. The new rules
are used to calculate a few mechanical quantities pertinent to the periodic
motions of celestial bodies. Several values have been obtained which result in
reasonable agreement with the corresponding experimental data. A gravitational
dimensionless structure constant has been determined, using the data relative
to the solar sistem, which allows to quantitatively account for phenomena on a
much wider scale. In particular, some information is acquired about the
recently discovered extrasolar planetary systems and about the general
empirical law which connects the spin of a celestial body with the square of
its mass.
