Dr. Van Altena will continue his Southern Proper Motion (SPM) program. These are second epoch observations, the first epoch data were obtained between 1965 and 1974, which are taken at the Yale Southern Observatory at El Leoncito, Argentina. The goal of the project is to determine the absolute proper motions of stars with respect to faint galaxies. The 20-year difference in the two data sets should result in highly accurate measurements of proper motions. The absolute proper motions will be used to determine the absolute magnitudes of RR Lyrae stars, corrections to the constants of precession, a fixed reference frame for the HIPPARCOS astrometric satellite, Oort's constant B, and to study the local structure of the Galaxy. The problems associated with establishing an inertial reference frame have occupied astronomers for millenia. With the passage of time and improvements in measurement techniques, it was discovered that the stars are not fixed in the sky and that it is necessary to separate the motions of the stars from that of the Earth's pole. This separation is currently made through the observation of Solar System objects such as the Sun, the planets, and minor planets. However, some of the Solar System observations are made in modes that differ significantly from those used in normal stellar observatons, and this difference may compromise the connection between the dynamically defined reference frame and the stellar frame. As a result, astronomers are left with star streams, moving groups, and non-circular motions in the Galaxy to complicate the stellar motion model and the derivation of the corrections to the constants of precession. The initial impetus for determining proper motions with respect to faint galaxies was to determine the corrections to the constants of precession and thereby improve on the system of the fundamental catalogs.
