defined 
   using the spin sense of the body.  Longitude is positive to the 
   west if the spin is prograde and positive to the east if the spin 
   is retrograde.  The spin sense is given by the sign of the first 
   degree term of the time-dependent polynomial for the body's prime 
   meridian Euler angle &quot;W&quot;:  the spin is retrograde if this term is 
   negative and prograde otherwise.  For the sun, planets, most 
   natural satellites, and selected asteroids, the polynomial 
   expression for 