Solar system and small-field astrometry

Astrometric issues for solar system studies are discussed. An overview gives references and cover all aspects of the solar system where astrometry is important: orbits of planets, moons, asteroids and NEOs, masses of asteroids, occultations of asteroids and KBOs, and families of asteroids and KBOs. The roles of astrometry from the ground, from Gaia and from a Gaia successor are discussed, but not small-field astrometry from space. It appears from work with CCD cameras at the 1.55 m astrometric reflector in Flagstaff that an accuracy of 1 mas is the best possible from the ground during one night observing when using ordinary telescopes, i.e. without wave-front correctors, and for field sizes larger than 2 arcmin. It has been seen that the same accuracies can be reached with the much larger 4-m class telescope on Hawaii although it is not specifically designed for astrometry. The accuracy of 1 mas from the ground refers mainly to non-moving point sources, but it is expected that 1 mas can be reached from the ground for solar system bodies from many nights of observations when phase effects are taken into account.