The Horizons On-Line Ephemeris and Data System ("Horizons" for short) is a computer program that provides data on the locations, motions, and dynamical parameters of solar-system objects, including the Sun, nine planets, 61 natural satellites, more than 16,000 comets and asteroids, and several dynamical points. Designed to be the reference standard for solar-system dynamical astronomy, Horizons is more comprehensive than any ephemeris or almanac published before in paper or software, and its data are the most accurate available from any source. Designed for use by professionals, Horizons can also be used by others; it is maintained on a server computer and is accessible to the public via the Internet. A user is given the best information available at the time of use. Horizons operates in multiple coordinate systems, includes a many-body integrator that propagates asteroid and comet orbits, and provides a search capability for identification of astronomical objects from parameters specified by the user.

This work was done by Jon D. Giorgini and Donald Yeomans of Caltech forNASA's Jet Propulsion Laboratory. Further information should be requested via the Internet from .

This software is available for commercial licensing. Please contact Don Hart of the California Institute of Technology at (818) 393-3425. Refer to NPO-20416.

NASA Tech Briefs Magazine

This article first appeared in the October, 1999 issue of NASA Tech Briefs Magazine.

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