IDL JPL Ephemeris and Solar System Timing: "IDL JPL Ephemeris and Solar System Timing

JPLEPHEM - Read and Interpolate JPL Planetary Ephemeris
This package provides routines to open, read, and interpolate the JPL Planetary Ephemeris in FITS format. The JPL ephemerides provide the positions and motions of the major planetary bodies in the solar system, including the earth, moon and sun, to very high precision. The JPL ephemerides are provided as blocks of Chebyshev coefficients, which, when interpolated, reproduce the original JPL numerical integrations within 1.5 cm."

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Home Page of Craig Markwardt
http://cow.physics.wisc.edu/~craigm/