JPL Horizons On-Line Ephemeris System
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JPL Horizons On-Line Ephemeris System provides easy access to key Solar System data and flexible production of highly accurate ephemerides for Solar System objects.
Osculating elements at a given epoch are always an approximation to an object's orbit (i.e. an unperturbed conic orbit or a "two-body" orbit). The real orbit (or the best approximation to such) considers perturbations by all planets, a few of the larger asteroids, a few other usually small physical forces, and requires numerical integration.
Jet Propulsion Laboratory (JPL) ephemerides do not use things such as periods, eccentricities, etc. Instead, JPL integrates the equations of motion in Cartesian coordinates (x,y,z), and adjusts the initial conditions in order to fit modern, highly accurate measurements of planetary positions.
- Alan B. Chamberlin (2006-02-28). "Frequently Asked Questions (FAQ): What's the exact value of..." JPL Solar System Dynamics. Retrieved 2011-01-20.
- Jet Propulsion Laboratory (August 28, 2015). "HORIZONS User Manual". "Long term ephemeridies" section. Retrieved January 10, 2016.