EPH

 EPH is a library of ANSI C functions that implements the ELP/MPP02 and VSOP2010 analytical lunar and planetary ephemerides (from l'Observatoire de Paris). EPH is appropriate for applications that require high accuracy without the need to download and interpolate files containing numerically integrated ephemerides.

Two example applications are provided:

  • occultation.c predicts the occultation of a planet by the Moon (to fraction of a second accuracy) as seen from a specified site.

  • planets.c lists the topocentric apparent places of Sun, Moon and planets (to milliarcsecond accuracies) at a given site and time.

    The calculations call functions from the IAU SOFA library.

    The EPH ephemerides are with respect to ICRS axes as implemented in JPL DE405.

    The adoption of VSOP2010 for EPH was for consistency with DE405, the more recent VSOP2013 having instead been fitted to INPOP10a (IMCCE, Observatoire de Paris). Users need to be aware that although the agreement between the different numerically integrated ephemerides is generally very good—for geocentric directions, milliarcsecond level—this falls off by 2-3 orders of magnitude for the outer planets.

    The user guide is eph.pdf and the files are in eph.zip

    Patrick Wallace, 3-Sep-2025