Sergei Klioner is one of the leading workers in the field of relativistic effects in astrometry at the micro-arcsec level. His 2003 Astronomical Journal paper on "A Practical Relativistic Model for Microarcsecond Astrometry in Space" is being used as one of the formulations for the Gaia relativistic development. Working at the Lohrmann Observatory, Dresden, with Michael Soffel, Sergei is an active member of the Gaia working group on relativity and reference frames.
Sergei's homepage is here.
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