Relativistic theory of astrometric observations. I Determination of the positions of remote sources from the surfaces of solar-system bodies

Equations for the rectangular components of the unit vector in the apparent direction toward a remote cosmic source are obtained within the framework of the post-Newtonian approximation of the GTR. It is assumed that the astronomical observations are made from the surface of a celestial body which is in an arbitrary heliocentric orbit. All relativistic corrections due to the solar gravitational field and the motion of the observer are taken into account in the resulting observational relations within the limits of the adopted accuracy of the calculations.