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I am working on an orbital dynamics code and, for fun, I would like to model the Sun-Earth-Moon system with my code. I can look up the masses of each object just fine, as well as average distances and relative velocities (which I can also calculate). However, I would like to model the Sun-Earth-Moon system in great detail. I would like to know the positions and velocities of each object on any given day (today works just fine) so that I can represent the orbits of these objects with great accuracy, hopefully even reproducing their actual ellipticity. Where can I find values for:

  • current Sun-Earth distance
  • current Earth-Moon distance
  • current Sun-Moon angular separation
  • current velocity of Earth relative to Sun (or relative to Sun-Earth(-Moon?) center of mass)
  • current velocity of Moon relative to Earth

and, maybe even

  • current velocity of Sun relative to Sun-Earth(-Moon?) center of mass.

Is there any resource that provides these current values?

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Is there any resource that provides these current values?

Yes. The JPL HORIZONS on-line solar system data and ephemeris computation service provides these values, and much more.

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    $\begingroup$ If you need continuous values, you can also look at NASA's SPICE files. $\endgroup$
    – user21
    Dec 18, 2014 at 22:18
  • $\begingroup$ @barrycarter -which is naif.jpl.nasa.gov $\endgroup$ Dec 19, 2014 at 3:52

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