On any given night, the planets look stationary against the background stars. But watch over a period of a few days for Venus or Mars (with orbital periods of 225 days and 1.88 years) and you can easily see why they are called planets, from Greek, meaning wanderers. Farther out, Jupiter and Jupiter and Saturn (11.9 and 29.4 years) take longer for movement to be noted, but move they do. Farther out yet are much slower moving Uranus and Neptune (83.7 and 163.7 years), but even these slowly trace their orbital courses against the stellar scene. Most of the times the planets move directly, to the east through the constellations of the Zodiac. But as our Earth laps the slower-moving outer planets (or as the faster inner planets lap us), they seem to stop and go backward into retrograde. Direct motion is shown below by Venus and Mars and by Uranus, while retrograde is seen for both Jupiter and Saturn.
|Then follow Uranus as it passed through Aquarius some four years later, seen here on October 9, 2004.|
|It took Uranus another six years to make it to southwestern Pisces, where it accompanied Jupiter, as seen on October 2, 2010. On the other hand, during the 10 years since it was last in Taurus (as seen above), Jupiter had moved more than three-fourths of the way around the sky.|
|Uranus is speedy compared to Neptune. After a full nine years, the more distant planet (see here on November 8, 2010) had not even made it out of Capricornus. Neptune is seen close to its 1846 discovery position (the actual anniversary on July 12, 2011). While it has gone around but once since it was found, Jupiter has circled the Sun some 14 times.|