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Astronomical Applications Department, U.S. Naval Observatory - novas c 2 doc
starvectors utility Converts RA, declination, proper motion, etc., to position and
velocity vectors.
nutation_angles basic Evaluates nutation series.
fund_args basic Computes fundamental arguments (mean elements) of the Sun and
earthtilt basic Provides information on orientation of Earth's axis: obliquity,
nutation parameters, etc.
cel_pole basic Allows for the specification of celestial pole offsets for high-
precision applications.
set_body basic Creates a structure of type
defining a solar system object
based on input parameters.
ephemeris basic Retrieves the position and velocity of a body from a fundamental
make_cat_entry basic Creates a structure of type
containing catalog data for
a star or "star-like" object.
refract basic Computes approximate refraction in zenith distance for optical
tdb2tdt basic Converts Terrestrial Time (TT or TDT) to Barycentric Dynamical
Time (TDB).
julian_date basic Computes the Julian date for a given calendar date (year, month,
day, hour).
cal_date basic Computes a date on the Gregorian calendar given the Julian date.
3.2 Ephemeris 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. Thus, an
ephemeris of the Earth is the minimum requirement.
NOVAS-C accesses ephemerides of solar system objects through function ephemeris.
This function, as supplied in NOVAS-C 2.0, supports access to an ephemeris of the major
solar system bodies (Sun, Moon, and the nine planets), and provides direct support for
access to the USNO minor planet ephemerides (USNO/AE98). In order to access the
ephemeris of major solar system bodies, function ephemeris calls function solarsystem.
While solarsystem 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.
3.2.1 Major Planets, Sun, and Moon
Files jplint.f and solsys2.c contain the software that serves as the interface between
NOVAS-C and the JPL lunar and planetary ephemerides, such as DE200, DE405, or
DE406. Subroutine jplint contains a single call to JPL's Fortran subroutine pleph, which

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