retrograde

Having a rotational or orbital movement that is opposite to the movement of most bodies within a celestial system. In the solar system, retrograde bodies are those that rotate or orbit in a clockwise direction (east to west) when viewed from a vantage point above the Earth's north pole. Venus, Uranus, and Pluto have retrograde rotational movements. No planets in the solar system have retrograde orbital movements, but four of Jupiter's moons exhibit such movement.

Having a brief, regularly occurring, apparently backward movement in the sky as viewed from Earth against the background of fixed stars. Retrograde movement of the planets is caused by the differing orbital velocities of Earth and the body observed. For example, the outer planets normally appear to drift gradually eastward in the sky in relation to the fixed stars; that is, they appear night after night to fall a little farther behind the neighboring stars in their westward passage across the sky. However, at certain times a particular planet appears briefly to speed up and move westward a bit more quickly than the neighboring stars. This happens as Earth, in its faster inner orbit, overtakes and passes the planet in its slower outer orbit; the appearance of moving counter to its usual eastward drift is thus simply the result of perspective as seen from Earth. Compare prograde.