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SLA_PLANTE - $[\,\alpha,\delta\,]$ of Planet from Elements

ACTION:
Topocentric apparent $[\,\alpha,\delta\,]$ of a Solar-System object whose heliocentric orbital elements are known.

CALL:
CALL sla_PLANTE ( DATE, ELONG, PHI, JFORM, EPOCH, ORBINC, ANODE, PERIH, AORQ, E, AORL, DM, RA, DEC, R, JSTAT)

GIVEN:

DATE D MJD of observation (JD-2400000.5)
ELONG,PHI D observer's longitude (east +ve) and latitude
radians)
JFORM I choice of element set (1-3, see Note 4, below)
EPOCH D epoch of elements (t0 or T, TT MJD)
ORBINC D inclination (i, radians)
ANODE D longitude of the ascending node ($\Omega$, radians)
PERIH D longitude or argument of perihelion ($\varpi$ or $\omega$,
radians)
AORQ D mean distance or perihelion distance (a or q, AU)
E D eccentricity (e)
AORL D mean anomaly or longitude (M or L,
radians, JFORM=1,2 only)
DM D daily motion (n, radians, JFORM=1 only)

RETURNED:

RA,DEC D topocentric apparent $[\,\alpha,\delta\,]$ (radians)
R D distance from observer (AU)
JSTAT I status:
0 = OK
-1 = illegal JFORM
-2 = illegal E
-3 = illegal AORQ
-4 = illegal DM
-5 = numerical error

NOTES:
1.
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).
2.
The longitude and latitude allow correction for geocentric parallax. This is usually a small effect, but can become important for Earth-crossing asteroids. Geocentric positions can be generated by appropriate use of the routines sla_EVP and sla_PLANEL.
3.
The elements are with respect to the J2000 ecliptic and equinox.
4.
Three different element-format options are available, as follows.

JFORM=1, suitable for the major planets:


 		 EPOCH 		 = 		 epoch of elements t0 (TT MJD)
		 ORBINC 		 = 		 inclination i (radians)
		 ANODE 		 = 		 longitude of the ascending node $\Omega$ (radians)
		 PERIH 		 = 		 longitude of perihelion $\varpi$ (radians)
		 AORQ 		 = 		 mean distance a (AU)
		 E 		 = 		 eccentricity e 
		 AORL 		 = 		 mean longitude L (radians)
		 DM 		 = 		 daily motion n (radians)        

JFORM=2, suitable for minor planets:


 		 EPOCH 		 = 		 epoch of elements t0 (TT MJD)
		 ORBINC 		 = 		 inclination i (radians)
		 ANODE 		 = 		 longitude of the ascending node $\Omega$ (radians)
		 PERIH 		 = 		 argument of perihelion $\omega$ (radians)
		 AORQ 		 = 		 mean distance a (AU)
		 E 		 = 		 eccentricity e 
		 AORL 		 = 		 mean anomaly M (radians)        

JFORM=3, suitable for comets:


 		 EPOCH 		 = 		 epoch of perihelion T (TT MJD)
		 ORBINC 		 = 		 inclination i (radians)
		 ANODE 		 = 		 longitude of the ascending node $\Omega$ (radians)
		 PERIH 		 = 		 argument of perihelion $\omega$ (radians)
		 AORQ 		 = 		 perihelion distance q (AU)
		 E 		 = 		 eccentricity e
5.
Unused elements (DM for JFORM=2, AORL and DM for JFORM=3) are not accessed.


next up previous
Next: SLA_PM - Proper Motion
Up: SUBPROGRAM SPECIFICATIONS
Previous: SLA_PLANET - Planetary Ephemerides

SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk