An influence of the matter distribution on the positional accuracy of reference sources

We consider an influence of a non-stationary gravitational field of the Galaxy on the visible positions of extragalactic sources. A contribution of the baryonic component of the galactic matter as well as of the hidden matter (including a population of brown dwarfs) were took into account. The observed variations of the deflection angle of light rays in a gravitational field of randomly moving point-like masses can be considered as a stochastic process. Using such an approach we constructed an autocorrelation function of studied stochastic process and found that its relative changes are about 15% for one year and about 35% for ten years.