ephemeris.c File Reference

Functions that allow to define or access Solar-system ephemeris data. More...

Functions
short	ephemeris (const double *restrict jd_tdb, const object *restrict body, enum novas_origin origin, enum novas_accuracy accuracy, double *restrict pos, double *restrict vel)
	Retrieves the position and velocity of a solar system body using the currently configured plugins that provide them.
novas_ephem_provider	get_ephem_provider ()
	Returns the user-defined ephemeris accessor function.
novas_nutation_provider	get_nutation_lp_provider ()
	Returns the function configured for low-precision IAU 2000 nutation calculations instead of the default nu2000k().
novas_planet_provider	get_planet_provider ()
	Returns the custom (low-precision) ephemeris provider function for major planets (and Sun, Moon, SSB...), if any.
novas_planet_provider_hp	get_planet_provider_hp ()
	Returns the custom high-precision ephemeris provider function for major planets (and Sun, Moon, SSB...), if any.
int	set_ephem_provider (novas_ephem_provider func)
	Sets the function to use for obtaining position / velocity information for minor planets, or satellites.
int	set_nutation_lp_provider (novas_nutation_provider func)
	Set the function to use for low-precision IAU 2000 nutation calculations instead of the default nu2000k().
int	set_planet_provider (novas_planet_provider func)
	Set a custom function to use for regular precision (see NOVAS_REDUCED_ACCURACY) ephemeris calculations instead of the default solarsystem() routine.
int	set_planet_provider_hp (novas_planet_provider_hp func)
	Set a custom function to use for high precision (see NOVAS_FULL_ACCURACY) ephemeris calculations instead of the default solarsystem_hp() routine.

Detailed Description

Functions that allow to define or access Solar-system ephemeris data.

SuperNOVAS cannot, by itself, provide accurate positions for Solar-system sources. While it has a built-in calculator (see solsys3.c) for the Earth and the Sun, it is suitable for obtaining approximate positions for the Sun and Earth only, and is limited to around 10 arcsec accuracy, typically.

To do astrometry right for Solar-system sources (major planets, and minor bodies like asteroids, comets, or moons), you will have to interface SuperNOVAS with ephemeris data, through a library or service. For example, NASA JPL provides short and long-term ephemeris data for all known Solar-system sources.

Besides providing accurate astrometric positions for Solar-system sources, planetary ephemeris data are also necessary for high-precision position calculations for sidereal (non-Solar-system) sources if one is to account for gravitational deflections around the major planets as light traverses the Solar-system on its way to the observer.

You may download various ephemeris data files (SPICE kernels) made available by NASA from the JPL NAIF site or from the JPL Horizons system, and them access them via appropriate C libraries, such as JPL's own NAIF CSPICE Toolkit, or the more modern CALCEPH library by IMCCE. SuperNOVAS provides interfaces to both (see solsys-cspice.c and solsys-calceph.c), making it very easy to incorporate ephemeris data into SuperNOVAS that way.

Alternatively, you might use some other library or your own code to access ephemeris data, e.g. by interfacing directly to the JPL Horizons system, or to the IAU Minor Planet Center (MPC). You can always write your own novas_ephem_provider function and activate it for SuperNOVAS with set_ephem_provider(), and also configure it to use for planets with:

set_planet_provider(planet_ephem_provider);
set_planet_provider_hp(planet_ephem_provider_hp);

(Alternatively, you might define separate low and high-precision ephemeris provider functions for the major planets ,by writing your own novas_ephem_provider and novas_ephem_provider_hp interface functions, respectively, and activating these with set_ephem_provider() and set_ephem_provider_hp().)

Date

Created on Mar 6, 2025

Author

Attila Kovacs and G. Kaplan

See also

solsys-calceph.c, solsys-cspice.c, solsys3.c, orbital.c