  Cosmic parallax is the change of angular separation between pair of sources
at cosmological distances induced by an anisotropic expansion. An accurate
astrometric experiment like Gaia could observe or put constraints on cosmic
parallax. Examples of anisotropic cosmological models are Lemaitre-Tolman-Bondi
void models for off-center observers (introduced to explain the observed
acceleration without the need for dark energy) and Bianchi metrics. If dark
energy has an anisotropic equation of state, as suggested recently, then a
substantial anisotropy could arise at $z \lesssim 1$ and escape the stringent
constraints from the cosmic microwave background. In this paper we show that
such models could be constrained by the Gaia satellite or by an upgraded future
mission.
