What retrograde motion is

The geometry

Everything in the solar system orbits the Sun in the same direction, and nothing stops or reverses. What changes is the angle we see it from. Earth is itself moving, at about 30 km per second, and a planet's apparent position is the line drawn from a moving observer to a moving object. When the two motions combine in a particular way, the line sweeps backwards for a few weeks or months, and the planet traces a loop or a zigzag against the stars.

The everyday comparison is overtaking on a motorway. As you draw level with a slower car and pass it, the car appears to drift backwards against the hedges behind it, even though it is still moving forwards. Neither car has changed speed. Only the sightline has.

Outer planets and inner planets do it differently

For Mars, Jupiter, Saturn, Uranus, Neptune and Pluto, the retrograde happens around opposition — the point where Earth, on the faster inside track, passes between the planet and the Sun. That is also when the planet is closest and brightest, which is why a retrograde outer planet is the best time to look at one through a telescope. The further out the planet, the longer the retrograde: Mars turns back for roughly ten weeks every twenty-six months, while Pluto spends nearly half of every year retrograde.

Mercury and Venus are inside Earth's orbit, so their retrogrades happen at inferior conjunction, when they swing between Earth and the Sun. Mercury does this three or four times a year for about three weeks at a time; Venus does it once every nineteen months or so, for about six weeks, and traces the five-pointed pattern over eight years that older texts make much of. The Sun and the Moon never retrograde at all.

Stations and shadow periods

A station is the moment the apparent motion changes sign. The planet slows, appears to hang at one degree for a day or more, and then moves the other way. Astrologically a station is read as the strongest point of the whole cycle, because the planet is dwelling on a single degree rather than passing through.

The shadow periods are the stretches either side, defined by the degrees the planet will cover three times in total. The pre-shadow begins when the planet first reaches the degree it will later retrograde back to; the post-shadow ends when it finally clears the degree it stationed at. Between those two dates the same band of the zodiac is crossed forwards, backwards, and forwards again, which is why the dated pages give a longer total than the retrograde itself.

What the tradition reads into it

The reading convention is old and simple: a retrograde body's significations turn inward and backward, so the matters it governs become subjects for review rather than for advance. Mercury retrograde is read for wording, contracts and travel arrangements; Venus retrograde for what you value and who reappears; Mars retrograde for drive that has gone quiet. The advice that follows is worth keeping narrow — check work you would otherwise wave through — because the broad version, in which a retrograde period is a general curse on ordinary life, has no support even inside the tradition that produced it.

It is worth keeping two things apart. That a planet appears to reverse is a fact about geometry, and can be checked with a telescope on any two nights a fortnight apart. That the reversal means review rather than advance is a convention about reading, handed down rather than measured. The dated pages give both, and label which is which.

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