Direction and redshift drifts for general observers and their
  applications in cosmology
  High precision astrometry now enables to measure the time drift of
astrophysical observables in real time, hence providing new ways to probe
different cosmological models. This article presents a general derivation of
the redshift and direction drifts for general observers. It is then applied to
the standard cosmological framework of a Friedmann-Lemaitre space- time
including all effects at first order in the cosmological perturbations, as well
as in the class of spatially anisotropic universe models of the Bianchi I
family. It shows that for a general observer, the direction drift splits into a
parallax and an aberration drifts and order of magnitude estimates of these two
components are provided. The multipolar decomposition of the redshift and
aberration drifts is also derived and shows that the observer's peculiar
velocity contributes only as a dipole whereas the anisotropic shear contributes
as a quadrupole.
