DE400

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DE400 (DE403, DE405, DE406, etc) are designations for the more recent members of a series of astronomical ephemerides produced by numerical integration at the Jet Propulsion Laboratory. ('DE' stands for Development Ephemeris.) The ephemerides of the DE4xx series are expressed in coordinates referred to the ICRF (International Celestial Reference Frame). The data are stored and distributed in the form of data files containing Chebyshev coefficients, along with source codes for access and basic data-processing to recover positions and velocities, thus amounting to software packages that provide a means of re-generating the positions and velocities of the underlying respective JPL Planetary and Lunar Ephemerides.^[1]

These ephemerides provide rectangular (solar-system barycentric) coordinates of position and velocity for the Earth-Moon barycenter, Sun and eight major planets, and geocentric coordinates of the Moon, all with respect to the International Celestial Reference Frame. The data enable derivation of geocentric or heliocentric coordinates of relevant bodies.

Available are data files (of documented format) with sets of Chebyshev polynomials, and also a few FORTRAN routines which can be used to evaluate the Chebyshev polynomials and interpolate the resulting planetary and lunar coordinates to high precision. DE405 accuracy for the inner planets is about 0.001 arcseconds (equivalent to about 1 km at the distance of Mars); for the outer planets it is generally about 0.1 arcseconds. The 'reduced accuracy' DE406 ephemeris gives an interpolating accuracy (relative to the full ephemeris values) no worse than 25 metres for any planet and no worse than 1 metre for the moon.

Documentation for later JPL ephemerides points out the availability of (independently produced) C and Java interpolating routines.

Nevertheless, the documentation indicates that the ephemerides in this form are not intended for a casual user. They are available for download by anonymous FTP.^[2]