After 44 years of research at an observatory in the foothills of the Andes, astronomers are nearing the end of a monumental undertaking: tracking the motion of 100 million stars. The Yale/San Juan Southern Proper Motion project, led by William van Altena, a professor emeritus of astronomy, has catalogued the proper motion of the celestial objects that light up the sky of the southern hemisphere. But the project's completion comes at a time when interest in astrometry - the science of measuring the position and motion of stars - is rapidly dwindling in the United States.