← Encyclopedia of Astrology · lesson 121/235
Planetary speed
What it measures
A planet's speed, or daily motion, is how far it travels along the zodiac in twenty-four hours, in degrees and minutes. The Moon covers about 13° a day; Saturn, about two minutes of arc. Speed is read from the ephemeris by comparing a planet's position on two successive days, as Lilly teaches his readers to do: Mars at 13°55′ Capricorn one noon and 14°41′ the next "so the Diurnall motion of Mars is 46 min."
Seen from the Earth, no planet keeps an even pace. The planets move in ellipses, and the Earth is moving too, so each one speeds up, slows down and, except for the Sun and Moon, periodically appears to stop and go backwards. Speed therefore says something about a planet's condition at that moment, not only about which planet it is.
Mean motion: the yardstick
Each planet has a mean motion, its average daily pace. Rough figures, as the tradition gives them:
| Body | Mean daily motion | Notes |
|---|---|---|
| Moon | about 13°10′ | from under 12° to over 15° |
| Sun | about 0°59′ | Lilly: from about 57′ to 61′ |
| Mercury, Venus | the Sun's pace on average | both swing widely either side of it, and turn retrograde |
| Mars | about 0°31′ | |
| Jupiter | about 0°05′ | |
| Saturn | about 0°02′ | |
| Uranus, Neptune, Pluto | under a minute |
Mercury and Venus never stray far from the Sun, so on average they keep its pace; but Mercury can run at nearly 2° a day and Venus at well over a degree, and both slow to a halt when they turn.
A planet moving faster than its mean is swift in motion (older authors also say "increasing in number"); one moving more slowly is slow in motion, or "slow of course".
Why swiftness was counted as strength
In Lilly's table of accidental fortitudes, a planet swift in motion gains 2 points and one slow in motion loses 2 — a small weight beside house and dignity, but a real one (accidental dignity). The reasoning is practical: a swift planet gets where it is going. In horary and electional work the significators' speed bears directly on whether and when a matter comes about. Lilly's aphorism is plain: "A Planet that is slow in motion, prolongs the thing quesited after, so that it's hardly performed." deVore notes that the Moon running faster than her mean was regarded as fortunate, and a slow Moon as a debility, especially in horary.
In a birth chart speed matters less, and modern astrologers seldom weigh it, though some read a slow planet as working steadily and thoroughly, and a fast one as quick to act and quick to move on.
Stations and retrogradation
As a planet approaches the point where it seems to reverse, its speed falls towards nothing: it is stationary — a station. It then moves backwards for a time, retrograde, with a negative speed, slows to a second station and resumes direct motion. deVore notes that the Sun and Moon are never stationary.
A stationing planet sits on almost the same degree for days or weeks, so whatever it touches it touches for a long time; many astrologers read a planet at its station as emphasised, its theme concentrated. Lilly scored direct motion (+4) and retrogradation (−5) separately from swiftness, so a planet can be both direct and slow, as it is just before or after a station.
How speed is used and shown here
The Planets table has a Speed column: the body's motion in degrees per day at the moment of the chart, to four decimal places. A negative number means the planet is retrograde, which the R column marks as well; a number close to zero means it is near a station.
Speed is put to work in three places. Whether an aspect is applying or separating is worked out from each body's actual speed, so a retrograde planet is handled correctly. Horary charts weigh a significator's swiftness against its mean motion with Lilly's +2 and −2. And an electional chart notes the Moon's own pace: swift (about 14° a day or more) counts in favour of a matter moving quickly, slow (about 12° or less) as a sign that it may drag. These are inclinations, weighed with everything else in the chart, never a verdict on their own.