Planetary Ephemerides

Top  Previous  Next

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, and De430 are provided with FreeFlyer and contain data for Sun, Moon, the eight major planets, and Pluto. FreeFlyer will use the De430.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. De430 is the most recent and generally recommended file of the selection available.

 

The DE file is also used for computing nutation and precession effects. The computation of these effects is controlled by the NPUpdateInterval 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:
 

1.Position and Velocity (without “body interpolation”) of the following bodies:

(0) Mercury

(1) Venus

(2) Earth-Moon (BARYCENTER)

(3) Mars

(4) Jupiter

(5) Saturn

(6) Uranus

(7) Neptune

(8) Pluto

(9) Geocentric moon (GEOCENTER)

(10) Sun

2.Nutations in longitude and obliquity (of the above bodies)

3.Lunar Librations (if on file)

 

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.