Influence of the Galactic gravitational field on the positional accuracy
  of extragalactic sources. II Observational appearances and detectability
  We consider a possibility of detecting the jitter effect of apparent
celestial positions of distant sources due to local fluctuations of the Galaxy
gravitational field. It is proposed to observe two samples of extragalactic
sources (target and control) in different sky directions using the
high-precision radio interferometry. It is shown that on a scale of ~2 years,
it is possible to detect a systematic increase in the standard deviation of
measured arc lengths of pairs of target sources compared to the control ones at
the $3\sigma$-level if the accuracy of differential astrometric observations is
around 10 $\mu$as. For the current state-of-the-art accuracy of 30 $\mu$as
achieved at the KVN or VERA interferometers, which have shorter baselines in
comparison with VLBI, the target and control samples will differ only at the
2$\sigma$-level on the scale of 10 years. To achieve the $3\sigma$-level on
this time interval, it is necessary to improve the accuracy up to ~20 $\mu$as.
Other possible effects that can also affect the arc length measurements between
two sources are discussed, and an observational strategy to minimize them is
suggested.
