Michael+Soffel

The basic astronomical reference system for space missions like GAIA is the Barycentric Celestial Reference System (BCRS). From this a corresponding Geocentric- or Topocentric- Celestial Reference System can be deduced. The BCRS assumes the solar system to be isolated and it is asymptotically flat. Hence every mass-energy outside the solar system is neglected. We found ways to include the expansion of the universe in the BCRS. To this end the Robertson-Walker metric is rewritten in terms of local coordinates. The problem if the global Hubble expansion has local influences is also discussed. Orders of magnitude for such local cosmological effects are given.
 * The fundamental astronomical reference system for space missions and the expansion of the universe **
 * Michael Soffel, ** S.Klioner**, Lohrmann Observatory, ** ** Dresden ** ** Technical ** ** University **