An accurate theory of the Moon's spin-orbital
motion has been constructed by numerical integration.
Several phenomena capable of producing effects of at least
$10^{-4}$ arc seconds in the lunar physical librations have
been included, analysed, and for the most part presented
in previous papers. The present work deals with
the relativistic spin contributions acting on the
Earth-Moon system: (i) de Sitter precession of the
Earth reference frame, (ii) quasi-Newtonian torques
acting on the lunar physical librations. The latter effect
does not seem to have been studied yet. The global behaviour
of the resulting librations is presented and described.
The resulting magnitude of these librations is of the order
of a few $10^{-4}$ arc seconds and may reach one milliarcsecond.
Unlike the very faint relativistic contribution to the
Earth's rotation, the corresponding relativistic terms in
the Moon's rotational motion are not negligible with
respect to the present observational accuracy of the
lunar laser data. Consequently it would be appropriate to
consider them in models adjusted to the observations.
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