palPlantu
palPlantu
- Topocentric RA,Dec of a Solar-System object from universal elements
- Description:
- Topocentric apparent RA,Dec of a Solar-System object whose
heliocentric universal elements are known.
- Invocation:
- void palPlantu ( double date, double elong, double phi, const double u[13],
double
ra, double
dec, double
r, int
jstat ) {
- Arguments:
-
-
date = double (Given)
-
TT MJD of observation (JD-2400000.5)
-
elong = double (Given)
-
Observer's east longitude (radians)
-
phi = double (Given)
-
Observer's geodetic latitude (radians)
-
u = const double [13] (Given)
-
Universal orbital elements
- (0) combined mass (M
m)
- (1) total energy of the orbit (alpha)
- (2) reference (osculating) epoch (t0)
- (3-5) position at reference epoch (r0)
- (6-8) velocity at reference epoch (v0)
- (9) heliocentric distance at reference epoch
- (10) r0.v0
- (11) date (t)
- (12) universal eccentric anomaly (psi) of date, approx
-
ra = double
(Returned)
-
Topocentric apparent RA (radians)
-
dec = double
(Returned)
-
Topocentric apparent Dec (radians)
-
r = double
(Returned)
-
Distance from observer (AU)
-
jstat = int
(Returned)
-
status: 0 = OK
- -1 = radius vector zero
- -2 = failed to converge
- Notes:
- DATE is the instant for which the prediction is required. It is
in the TT timescale (formerly Ephemeris Time, ET) and is a
Modified Julian Date (JD-2400000.5).
- The longitude and latitude allow correction for geocentric
parallax. This is usually a small effect, but can become
important for near-Earth asteroids. Geocentric positions can be
generated by appropriate use of routines palEpv (or palEvp) and
palUe2pv.
- The "universal" elements are those which define the orbit for the
purposes of the method of universal variables (see reference 2).
They consist of the combined mass of the two bodies, an epoch,
and the position and velocity vectors (arbitrary reference frame)
at that epoch. The parameter set used here includes also various
quantities that can, in fact, be derived from the other
information. This approach is taken to avoiding unnecessary
computation and loss of accuracy. The supplementary quantities
are (i) alpha, which is proportional to the total energy of the
orbit, (ii) the heliocentric distance at epoch, (iii) the
outwards component of the velocity at the given epoch, (iv) an
estimate of psi, the "universal eccentric anomaly" at a given
date and (v) that date.
- The universal elements are with respect to the J2000 equator and
equinox.
-
See Also
- Sterne, Theodore E., "An Introduction to Celestial Mechanics",
Interscience Publishers Inc., 1960. Section 6.7, p199.
- Everhart, E. & Pitkin, E.T., Am.J.Phys. 51, 712, 1983.