  % context heading (optional) {Thanks to the Venus Express Mission, new data
on the properties of Venus could be obtained in particular concerning its
rotation.} % aims heading (mandatory) {In view of these upcoming results, the
purpose of this paper is to determine and compare the major physical processes
influencing the rotation of Venus, and more particularly the angular rotation
rate.} % methods heading (mandatory) {Applying models already used for the
Earth, the effect of the triaxiality of a rigid Venus on its period of rotation
are computed. Then the variations of Venus rotation caused by the elasticity,
the atmosphere and the core of the planet are evaluated.} % results heading
(mandatory) {Although the largest irregularities of the rotation rate of the
Earth at short time scales are caused by its atmosphere and elastic
deformations, we show that the Venus ones are dominated by the tidal torque
exerted by the Sun on its solid body. Indeed, as Venus has a slow rotation,
these effects have a large amplitude of 2 minutes of time (mn). These
variations of the rotation rate are larger than the one induced by atmospheric
wind variations that can reach 25-50 seconds of time (s), depending on the
simulation used. The variations due to the core effects which vary with its
size between 3 and 20s are smaller. Compared to these effects, the influence of
the elastic deformation cause by the zonal tidal potential is negligible.} %
conclusions heading (optional), leave it empty if necessary {As the variations
of the rotation of Venus reported here are of the order 3mn peak to peak, they
should influence past, present and future observations providing further
constraints on the planet internal structure and atmosphere.}
