Retrograde Planet
A retrograde planet is, as seen from Earth, a planet whose apparent motion temporarily reverses on the zodiac, giving the illusion that it is moving backward. The phenomenon is noted by the symbol R before the planet's name in a chart.
Origin and etymology
The phenomenon of retrogradation has been observed since Antiquity. Babylonian astronomers of the first millennium BCE already recorded its periods. The Latin word retrogradus means walking backward. Claudius Ptolemy, in the Almagest in the 2nd century, proposed a geocentric model with epicycles to account for this apparent motion. Nicolaus Copernicus in De revolutionibus (1543) and then Johannes Kepler resolved the mystery by showing that retrogradation is an optical illusion due to the relative motion of the planets around the Sun. Only Mercury, Venus, Mars, Jupiter, Saturn, and the trans-Saturnian planets can appear retrograde when viewed from Earth.
Evolution and tradition
Astronomically, planets retrograde at regular intervals: Mercury three times a year, Venus about every 18 months, Mars every two years, Jupiter each year, Saturn, Uranus, Neptune and Pluto several months a year. Astrologically, the medieval tradition considered a retrograde planet weakened. The modern re-reading, notably in Erin Sullivan and Diana McMahon Collis, sees retrogradation as an internalization: the planetary function expresses itself more reflexively, more subjectively. Mercury retrograde has become a popular phenomenon widely diffused beyond astrological circles.
Practical use
In a natal chart, a retrograde planet signals a function that expresses itself introspectively, sometimes against the current. A natal retrograde Mercury does not prevent you from thinking or communicating, but inscribes these activities within a more personal approach. In predictive astrology, retrograde periods, particularly those of Mercury, are traditionally discouraged for signing a contract, launching a project or buying a device. On Tarotoui, retrograde planets are identified in chart and transit calculations. This precaution, contested, remains very popular.
Going further
Retrogradation is a phenomenon of appearance, not a physical reality. No planet actually moves backward. Confusing retrogradation with a curse is a recent popular distortion. Statistical studies (Geoffrey Dean, Suitbert Ertel) have not confirmed any particular effect of Mercury retrograde on contracts or travel. Note that retrogradation is more marked for slow planets than for fast ones.