Retrograde motion is a orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is the central object (right figure). It may also describe other motions such as precession or nutation of the object's rotational axis.
In the Solar System, the orbits about the Sun of all planets and most other objects, except many comets, are prograde, i.e. in the same direction as the Sun rotates. The rotations of most planets, except Venus and Uranus, are also prograde. Most natural satellites have prograde orbits about their planets. Prograde satellites of Uranus orbit in the direction Uranus rotates, which is retrograde to the Sun. Retrograde satellites are generally small and distant from their planets, except Neptune's satellite Triton, which is large and close. All retrograde satellites are thought to have formed separately before being captured by their planets.