Advances in radio astrometry

Astrometry is the branch of astrophysics that studies the position and motion of celestial objects. Radio interferometers that span many thousands of kilometers are presently the most accurate astrometric instruments, and have pushed the angular accuracy to 10− arcsec = 5×10−11 rad. After a tutorial on the measurement and use of the visibility phase, we describe the two major aspects of astrometry...