Retrograde Motion is most often used in reference to the motion of the outer planets (Mars, Jupiter, Saturn, and so forth). Though these planets appear to move from east to west on a nightly basis in response to the spin of the Earth, they are actually drifting slowly eastward with respect to the stationary stars, which can be observed by noting the position of these planets for several nights in a row. This motion is normal for these planets, however, and not considered Retrograde Motion. However, since the Earth completes its orbit in a shorter period of time than these outer planets, we occasionally overtake an outer planet, like a faster car on a multiple-lane highway. When this occurs, the planet we are passing will first appear to stop its eastward drift, and it will then appear to drift back toward the west. This is Retrograde Motion, since it is in a direction opposite that which is typical for planets. Finally, as the Earth swings past the planet in its orbit, they appear to resume their normal west-to-east drift on successive nights.
O movemento retrógrado emprégase con maior frecuencia en referencia ao movemento dos planetas exteriores (Marte, Xúpiter, Saturno, etc.). Ainda que estes planetas semellen movérense do leste para o oeste cada noite en resposta ao movemento da Terra, realmente están derivando lentamente cara o leste en relación ás estrelas estacionarias, o que se pode observar anotando a posición destes planetas varias noites seguidas. Este movemento, porén, é normal nestes planetas e non se considera movemento retrógrado. Porén, dado que a Terra completa a súa órbita nun período de tempo menor do que estes planetas exteriores, en ocasións adiantamos un planeta exterior, como un vehículo máis rápido nunha autoestrada con varias faixas. Cando isto acontece, o planeta que estamos a adiantar parece que detén a súa deriva cara o leste e despois parece que volve a derivar de novo cara o leste. Este é movemento retrógrado, dado que que a Terra pasa rapidamente o planeta na súa órbita, parece que recuperan a súa deriva normal do oeste para o leste en noites posteriores.