Planet Position from Elements
CALL sla_PLANEL (DATE, JFORM, EPOCH, ORBINC, ANODE, PERIH,
AORQ, E, AORL, DM, PV, JSTAT)
DATE  D  TT MJD of observation (JD$$2400000.5, 
 

 Note 1) 
 
JFORM  I  choice of element set (13, Note 3) 
 
EPOCH  D  epoch of elements (${t}_{0}$ or $T$, TT MJD, Note 4) 
 
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) 
PV  D(6)  heliocentric $\left[\phantom{\rule{0.3em}{0ex}}x,y,z,\u1e8b,\u1e8f,\u017c\phantom{\rule{0.3em}{0ex}}\right]$, equatorial, J2000 
 

 (AU, AU/s) 
 
JSTAT  I  status: 
 

 0 = OK 
 

 $$1 = illegal JFORM 
 

 $$2 = illegal E 



 $$3 = illegal AORQ 



 $$4 = illegal DM 



 $$5 = numerical error 
JFORM=1, suitable for the major planets:
EPOCH  =  epoch of elements ${t}_{0}$ (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 ${t}_{0}$ (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 $e$ 
Unused elements (DM for JFORM=2, AORL and DM for JFORM=3) are not accessed.
Therefore, for any given problem there are up to three different epochs in play, and it is vital to distinguish clearly between them:
For the majorplanet and minorplanet cases it is usual to make the epoch that defines the position of the body the same as the epoch of osculation. Thus, only two different epochs are involved: the epoch of the elements and the epoch of observation. For comets, the epoch of perihelion fixes the position in the orbit and in general a different epoch of osculation will be chosen. Thus, all three types of epoch are involved.
For the present routine: