Precession Properties 
The Precession type exposes the following members.
Name  Description  

MeanObliquity 
Gets the mean obliquity of the ecliptic, in radians.
 
Theta 
Gets the accumulated precession angle theta, in radians, used to tilt the xyplane to the mean equator of date.
 
Z 
Gets the accumulated precession angle z, in radians, used to align the xaxis with the mean equinox of date by rotating
along the mean equator of date.
 
Zeta 
Gets the accumulated precession angle zeta, in radians, used to align the xaxis toward the direction in which
the pole is to be tilted off of the ICRF zaxis.
