DE400

DE400

DE400 (and 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. ('JPL DE' stands for Jet Propulsion Laboratory Development Ephemeris.) The ephemerides of the DE4xx series are expressed in coordinates referred to the ICRF (International Celestial Reference Frame). 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. These data enable derivation of geocentric or heliocentric coordinates of relevant bodies. From the issue for 2003 onwards, the Astronomical Almanac has been based on JPL ephemeris DE405.[1] The DE4xx series of ephemerides is an update to the DE200 ephemeris.[2]

The data have been made publicly available,[3] 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.[4]

Evaluation and interpolation of the Chebyshev polynomials can give 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.[5]

References

  1. ^ See US Naval Observatory (Naval Oceanography Portal), "History of the Astronomical Almanac" (accessed December 2009); also, for details of DE405:- E M Standish (1998), JPL Planetary and Lunar Ephemerides, DE405/LE405, Jet Propulsion Laboratory Interoffice Memorandum 312F-98-48, August 26, 1998.
  2. ^ Standish, et. al. (1997). "JPL Planetary and Lunar Ephemerides on CD-ROM". Willmann-Bell, Inc.. http://www.willbell.com/software/jpl.htm. 
  3. ^ See the JPL FTP site with ephemerides (data files), source code (for access and basic processing of the data to recover positions and velocities), and documentation.
  4. ^ See JPL Planetary and Lunar Ephemerides Export Information README.txt version of 12 Oct 2007. Also available is an older version README.txt version of December 6, 2005.
  5. ^ FTP directory /pub/eph/planets at ftp://ssd.jpl.nasa.gov

External links

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