Planetary Ephemerides

Highly accurate planetary ephemeris files are generated by NASA JPL and are used for determining the precise location of solar system objects. The Development Ephemeris (DE) files De200, De405, De418, De421, De430, and De440 are provided with FreeFlyer and contain data for Sun, Moon, the eight major planets, and Pluto. FreeFlyer will use the De440.dat file by default.

The DE file to use can be controlled in the Options à Preferences à User Preferences menu. The Planetary File item under the Data Files preferences page specifies the DE file to use.

Note: The De405 model (which contains nutations and librations) is considered slightly more accurate than the De200 model (nutations only), but the difference would be considered inconsequential for most Earth-centered orbits.

The DE file is also used for computing nutation and precession effects. The computation of these effects is controlled by the CIRFEvaluationMode flag of the SolarSystem object, which determines the frequency of computing the nutation and precession matrices.

Values used by FreeFlyer from the Planetary Ephemeris file:
 

FreeFlyer provides truncated versions of NASA JPL's full span planetary ephemeris files. If an epoch is before or after the end of the planetary ephemeris file's data span, FreeFlyer will report an error indicating that the states of the planetary bodies could not be computed for the requested date.

The truncated versions are generated by converting JPL's planetary ephemerides from the ASCII to Binary format using JPL's provided Fortran program. The planetary ephemeris ASCII files and Fortran instructions for converting into Binary files are available on JPL's "Planetary and Lunar Ephemerides" website.

The following planetary ephemeris files and data spans are provided with FreeFlyer: