Astronomical Applications Department, U.S. Naval Observatory NOVASC Page 6
In order to compute instantaneous positions using the supervisory functions, NOVAS-C must have
access to a solar system ephemeris. The solar system ephemeris provides NOVAS-C with the heliocentric
and barycentric positions and velocities of desired solar system objects referred to the mean equator and
equinox of J2000.0. The solar system ephemeris is required even when only precise star positions are
needed in that case, the "desired solar system object" is the Earth.
NOVAS-C accesses the ephemeris through a function called solarsystem. While this function has a
defined argument list, its inner workings can take any form depending upon the ephemeris that has been
selected for use. Users may write their own versions of solarsystem or use either of the two versions
provided with NOVAS-C:
such as DE200 or DE403. This function contains a single call to JPL's Fortran subroutine pleph, which in
turn calls other Fortran subroutines in the JPL ephemeris software package. The user must obtain the
Fortran ephemeris package from JPL, set up the binary, random-access ephemeris file, and link the
applicable JPL Fortran code with NOVAS-C. For more details, see the discussion of this version of
solarsystem in Section 4.
file. This version of solarsystem is ideally suited for computing coordinates of stars, with errors not
exceeding several milliarcseconds.
See the next section for additional information on function solarsystem and other frequently called
functions.
