Retrograde motion is motion in the direction opposite to the movement of something else and the contrary of
direct or
prograde motion. This
motion can be the
orbit of one body about another body or about some other point, or the
rotation of a single body about its
axis, or other phenomena such as
precession or
nutation of the axis. In reference to celestial
systems, retrograde motion
usually means motion which is contrary to the
rotation of the
primary, that is, the object which forms the system's hub.