  We discuss several results made possible by accurate SDSS astrometric
measurements in a large sky area, with emphasis on asteroids and stellar proper
motions obtained by comparing POSS and SDSS. SDSS has observed over 200,000
moving objects in five photometric bands, corresponding to about two orders of
magnitude increase over previous multi--color surveys. These data were used to
extend the measurement of asteroid size distribution to a smaller size limit,
to demonstrate that asteroid dynamical families, defined as clusters in orbital
parameter space, also strongly segregate in color space, and to discover a
correlation between asteroid age and colors. A preliminary analysis of
SDSS-POSS proper motions for about 1 million M dwarf stars demonstrates that,
in the 0.1-1 kpc distance range, the rotational velocity and its dispersion for
disk stars increase with the distance from the Galactic plane.
