Retrograde

every reader

What the tradition reads

A planet is retrograde when, seen from the Earth, it appears to move backward against the stars for a time, slowing first to a standstill at what the tradition calls its first station, reversing direction, and eventually slowing again to a second station before resuming its ordinary forward motion. The tradition reads a retrograde planet as turned inward, its usual outward business paused, delayed, or redirected toward review and revision rather than the fresh initiative the same planet shows when direct; a natal planet retrograde at birth is read as expressing that planet's nature in a more private, reworked or hesitant register throughout the life, while a transiting retrograde is read as a season for reconsidering rather than starting whatever that planet governs. The Sun and Moon, whose apparent motion around the Earth never reverses, are the only two traditional bodies never read as retrograde; among the rest, the outer, slower planets spend a considerably larger fraction of each year retrograde than the faster inner ones, so that a Mercury retrograde recurs several times a year while an outer planet's retrograde period may run for months at a stretch.

The story

Retrograde motion puzzled every geocentric astronomer who tried to explain it without abandoning the assumption that the Earth stood still at the centre of the heavens. The geocentric model proposed by Apollonius in the third century BCE, and refined by the astronomers who followed him, explained the puzzle with deferents and epicycles, small circles riding on larger ones, whose combined motion could reproduce a planet's observed backward loop without requiring the planet itself ever truly to reverse course. It was not until the heliocentric model set out by Copernicus, and confirmed by later observation, that retrograde motion was properly understood as pure illusion, the ordinary consequence of the Earth's own faster orbit periodically overtaking a slower outer planet and making it appear briefly to slip backward against the more distant stars, exactly as a car overtaking a slower one on a parallel road makes the slower car seem to inch backward for a moment. The word retrograde itself comes from the Latin retrogradus, a backward step, built from retro, backward, and gradus, a step, a name that describes only the observed appearance and carries no claim about what is actually happening in the sky.

Written from

Corpus key glossary:retrograde.