  With rapid development of techniques for astronomical observations, the
precision of measurements has been significantly increasing. Theories of
astronomical relativistic reference systems, which are the foundation for
processing and interpreting these data now and in the future, may require
extensions to satisfy the needs of these trends. Besides building a framework
compatible with alternative theories of gravity and the pursuit of higher order
post-Newtonian approximation, it will also be necessary to make the first order
post-Newtonian multipole moments of celestial bodies be explicitly expressed in
the astronomical relativistic reference systems. This will bring some
convenience into modeling the observations and experiments and make it easier
to distinguish different contributions in measurements. As the first step, the
global solar system reference system is multipolarly expanded and the
post-Newtonian mass and spin moments are shown explicitly in the metric which
describes the coordinates of the system. The full expression of the global
metric is given.
