Some aspects of relativistic astrometry from within the Solar system (Q1890144)

Aim of the fundamental astrometry is to measure stellar positions, parallaxes and proper motions directly from optical observations. Nowadays the European Space Agency is planning to launch not later that 2012 the space astrometry mission ( the satellite GAIA orbiting around the Sun) and it is expected to make astrometric measurements with a precision of a few \(\mu\)arcsec. Here the structure of a general relativistic astrometric model which has been developed to deduce the positions and proper motion of star from 1\(\mu\)arcsecond optical observations is outlined. There are two basic assumption used in the model: 1. The Solar System is the only source of gravity; 2. The Solar System is a source of a weak gravitational field.