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JPL Horizons On-Line Ephemeris System
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<p>JPL Horizons On-Line Ephemeris System provides access to key Solar System data and flexible production of highly accurate <a href="/facts/Ephemerides/vjQCBG29">ephemerides</a> for Solar System objects. </p><p><a href="/facts/Osculating_orbit/hA7omegY">Osculating elements</a> at a given <a href="/facts/Epoch_(astronomy)/RDdj6SmA">epoch</a> (such as produced by the <a href="/facts/JPL_Small-Body_Database/YQQLDXng">JPL Small-Body Database</a>) are always an approximation to an object's orbit (i.e. an unperturbed conic orbit or a "<a href="/facts/Two-body_problem/YCG4geSH">two-body</a>" orbit). The real orbit (or the best approximation to such) considers <a href="/facts/Perturbation_(astronomy)/og5hPpjQ">perturbations</a> by all planets, a few of the <a href="/facts/List_of_notable_asteroids/sm8zjMNC">larger asteroids</a>, a few other usually small physical forces, and requires <a href="/facts/Numerical_integration/MwJnvcDV">numerical integration</a>. </p><p><a href="/facts/Jet_Propulsion_Laboratory/zPXnxRBf">Jet Propulsion Laboratory</a> (JPL) ephemerides do not use things such as periods, eccentricities, etc. Instead, JPL integrates the <a href="/facts/Equations_of_motion/25msr1vE">equations of motion</a> in <a href="/facts/Cartesian_coordinate_system/lkTqvMmB">Cartesian coordinates</a> (x,y,z), and adjusts the initial conditions in order to fit modern, highly accurate measurements of planetary positions. </p><p>Since August 2013, Horizons has been using <a href="/facts/Ephemeris/vjQCBG29">ephemeris</a> <a href="/facts/Jet_Propulsion_Laboratory_Development_Ephemeris/SeCNLYkt">DE431</a>. During the week of 12 April 2021, the Horizons ephemeris system was updated to replace the DE430/431 planetary ephemeris, used since 2013, with the new DE440/441 solution. The new DE440/441 general-purpose planetary solution includes seven additional years of ground and space-based astrometric data, data calibrations, and dynamical model improvements, most significantly involving Jupiter, Saturn, Pluto, and the Kuiper Belt. Inclusion of 30 new Kuiper-belt masses, and the Kuiper Belt ring mass, results in a time-varying shift of ~100 km in DE441's barycenter relative to DE431. </p><p>In September 2021 JPL started transitioning from <a href="/facts/Common_gateway_interface/zWsLFXGJ">common gateway interface</a> (CGI) to <a href="/facts/Application_programming_interface/GMlN4vUr">application programming interface</a> (API). </p>