Planetocentric Systems

For solar system bodies the IAU differentiates between planetocentric and planetographic body-fixed coordinates : Planetocentric latitude refers to the equatorial plane and the polar axis, planetographic latitude is defined as the angle between equatorial plane and a vector through the point of interest that is normal to the biaxial ellipsoid reference surface of the body. Both latitudes are identical for a spherical body. Planetocentric longitude is measured eastwards (i.e. positive in the sense of rotation) from the prime meridian. Planetographic longitude of the sub-observation point increases with time, i.e. to the west for prograde rotators and to the east for retrograde rotators. All systems defined in the following are planetocentric.

Table 6 gives the orientation of the planetary rotation systems for all major planets at epoch $GEI_{J2000}$ and their change with time. These are defined by the equatorial attitude $(\alpha,\delta)$ of the rotation axis and the prime meridian angle $w_0$. Data are taken from [S. Table 15.7] which is identical to the table given by Davies et al. (1996). The ascending node right ascensions are given by $\Omega = \alpha + 90^\circ$. The respective transformation matrices are

$$T(GEI_{J2000},PLA_{J2000}) = E(\alpha_0 + 90^\circ, 90^\circ - \delta_0, W_0)$$ (37)

$$T(GEI_{J2000},PLA_{D}) = E(\alpha_0 + \dot{\alpha} T_0 + 90^\circ, 90^\circ - \delta_0 - \dot{\delta} T_0 , W_0 + \dot{W} d_0)$$

where $d_0$ and $T_0$ are defined in eqn.1 and 2.

Table 6: Physical Ephemeris of the Planets $GEI_{J2000}$[S. Table 15.7, A. E87]: $(\alpha _0,\delta _0)$ is the position of the North pole in $GEI_{J2000}$, $(\dot{\alpha},\dot{\delta})$ its change per Julian century $T$, $W_0$ is the position of the prime meridian at $GEI_{J2000}$, $\dot{W}$ its change per day

Name	$\alpha_0 [^\circ]$	$\dot{\alpha}[^\circ/T]$	$\delta_0 [^\circ]$	$\dot{\delta}[^\circ/T]$	$W_0[^\circ]$	$\dot{W}[^\circ/d]$
Sun	286.13		63.87		84.10	+14.1844000
Mercury	281.01	-0.003	61.45	-0.005	329.71	+6.1385025
Venus	272.72		67.15		160.26	-1.4813596
Earth	0.00	-0.641	90.00	-0.557	190.16	+360.9856235
Mars	317.681	-0.108	52.886	-0.061	176.868	+350.8919830
Jupiter III	268.05	-0.009	64.49	+0.003	284.95	+870.5360000
Saturn III	40.58	-0.036	83.54	-0.004	38.90	+810.7939024
Uranus III	257.43		-15.10		203.81	-501.1600928
Neptune	299.36	+0.70$\sin N$	43.46	-0.51$\cos N$	253.18	536.3128492-0.48$\sin N$
(where N=	359.28	+54.308)
Pluto	313.02		9.09		236.77	-56.3623195