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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

$\displaystyle T(GEI_{J2000},PLA_{J2000})$ $\textstyle =$ $\displaystyle E(\alpha_0 + 90^\circ, 90^\circ - \delta_0, W_0)$ (37)
$\displaystyle T(GEI_{J2000},PLA_{D})$ $\textstyle =$ $\displaystyle E(\alpha_0 + \dot{\alpha} T_0 + 90^\circ, 90^\circ - \delta_0 - \dot{\delta} T_0 , W_0 + \dot{W}

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 \bgroup\color{red}$\sin N$\egroup
(where N= 359.28 +54.308)        
Pluto 313.02   9.09   236.77 -56.3623195

next up previous
Next: Jovian Systems Up: Planetary Systems Previous: Position of Earth and
Markus Fraenz 2017-03-13