prograde and retrograde motion

The solar system originally accreted (essentially "condensed" by gravity) from a spinning disc of dust and rock called an accretion disc. As a consequence the majority of the planets and moons revolve around the Sun roughly on a single plane, called the plane of the ecliptic, and in a single direction, referred to as prograde. Seen from above Earth's north pole, prograde motion is anticlockwise. Bodies which orbit in the opposite direction are said to have retrograde motion.

Inconstant Moon