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Of the moon's rotational velocity perturbations due to the periodic tidal
torque. I just did a "back of the envelope" (actually more like "two
sheet of paper") derivation of the period for small oscillations of a
nearly spherical but slightly prolate ellipsoid in a gravitational field
gradient and got the sensible result that
T = 2 pi/sqrt(f g')
where f is the fractional difference between the maximum and minimum
rotational inertias about axes through the CM and g' is the local field
gradient. For the moon g' is about 1.4 x 10^-11 s^-2. I don't know the
value of f, but if it were as large as 1% (which I sincerely doubt), the
period would still be over 6 months.