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 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)

$$\Omega$$ ANODE D

$$\varpi \omega$$ PERIH D 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:

$$[\,\alpha,\delta\,]$$ RA,DEC

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.