  Extremely high precision of near-future radio/optical interferometric
observatories like SKA, Gaia, SIM and the unparalleled sensitivity of LIGO/LISA
gravitational-wave detectors demands more deep theoretical treatment of
relativistic effects in the propagation of electromagnetic signals through
variable gravitational fields of the solar system, oscillating and precessing
neutron stars, coalescing binary systems, exploding supernova, and colliding
galaxies. Especially important for future gravitational-wave observatories is
the problem of propagation of light rays in the field of multipolar
gravitational waves emitted by a localized source of gravitational radiation.
Present paper suggests physically-adequate and consistent mathematical solution
of this problem in the first post-Minkowskian approximation of General
Relativity which accounts for all time-dependent multipole moments of an
isolated astronomical system.
