JPL Horizons On-Line Ephemeris System
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 physical usually small forces, and requires numerical integration.
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.
There are 3 ways to use the system:
- Alan B. Chamberlin (2006-02-28). "Frequently Asked Questions (FAQ): What's the exact value of...". JPL Solar System Dynamics. Retrieved 2011-01-20.
- Acton (2013). "README.txt". file at the NAIF website.
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