  We used a series of COBOLD hydrodynamical model atmospheres covering stellar
objects from white dwarfs to red giants to derive theoretical estimates of the
photometric and photocentric stellar variability in wavelength-integrated light
across the Hertzsprung-Russell diagram. We validated our models against solar
measurements from the SOHO/VIRGO instrument. Within our set of models we find a
systematic increase of the photometric as well as photocentric variability -
which turn out to be closely connected - with decreasing surface gravity. The
estimated absolute levels of the photocentric variability do not affect
astrometric observations on a precision level expected to be achieved by the
GAIA mission - with the exception of close-by giants. The case of supergiants
remains to be investigated. In view of the ongoing debate about the photometric
non-detection of p-modes in Procyon by the Canadian MOST satellite we remark
that we obtain a factor of ca. 3 in amplitude between the granular background
noise in the Sun and Procyon. This statement refers to a particular
representation of temporal power spectra as discussed in Sect. 5.
