  This paper represents a first attempt of embedding the Barycentric Celestial
Reference System, the fundamental relativistic reference system to be used for
the modeling of Gaia observations, into some cosmological background. The
general Robertson-Walker metric is transformed into local coordinates where the
cosmological effects are represented as tidal potentials. A version of a
cosmological BCRS is then suggested to lowest order. The effects of
cosmological background on the motion of the solar system are estimated and
found to be completely negligible. The relation to the de Sitter and
Schwarzschild-de Sitter solutions is discussed.
