← Encyclopedia of Astrology · lesson 155/235
Perigee and apogee
What it is
The Moon's orbit is not a circle but an ellipse, so her distance from the Earth changes through the month. Her nearest point is perigee (Greek perí, near, and gê, earth); her farthest is apogee (apó, away). Together the two are the apsides of the orbit, and the line joining them slowly turns, going once round in about nine years.
| Typical distance | |
|---|---|
| Perigee | about 356,400–370,400 km |
| Mean distance | about 384,400 km |
| Apogee | about 404,000–406,700 km |
She passes from one perigee to the next in about 27.55 days, the anomalistic month, which is a little longer than her trip round the zodiac — see the Moon's months.
What changes
Speed. Following Kepler's second law, the Moon moves fastest at perigee and slowest at apogee. Her daily motion along the zodiac ranges from about 11.8° to about 15.4°, so she can spend a little under two days in a sign or a little over two and a half. Astrologers have long called a Moon "swift in motion" or "slow in motion", and Lilly counts a swift Moon among her accidental strengths.
Size and brightness. A Full Moon at perigee looks about 14% wider and up to about 30% brighter than one at apogee. The difference is real but hard to notice without a side-by-side comparison; the Moon near the horizon looks large for a different reason, a trick of perception.
Tides. The Moon's pull on the oceans is strongest at perigee. When a perigee falls close to a New or Full Moon, when the Sun's pull lines up with hers, tides run noticeably higher and lower than usual — the perigean spring tides.
Supermoon and micromoon
"Supermoon" is a modern word. The astrologer Richard Nolle coined it in 1979 for a New or Full Moon that falls when the Moon is within about 90% of her closest approach for that orbit. Astronomers have since adopted the word informally, usually for a Full Moon near perigee, and the press uses it a few times most years. Its opposite, a Full Moon near apogee, has come to be called a micromoon.
Nolle linked supermoons to strong tides and, more speculatively, to earthquakes and storms in the days around them. That second claim is his own and is not established; it is best read as part of the modern folklore of the Moon rather than a tradition.
In the tradition
The old authors knew the Moon's changing speed and size long before her orbit was understood. Ptolemy's model of the Moon includes an epicycle to account for it, and the electional writers preferred a Moon "increasing in number", that is, moving quickly, for anything meant to go forward briskly. Biodynamic gardening after Maria Thun treats the hours around perigee as unfavourable for sowing, and some modern almanacs carry the same caution.
How it is read
In astrology today a perigee Moon is often read as a stronger, more insistent Moon — feelings near the surface, events moving faster — and an apogee Moon as quieter and further off. A supermoon Full or New Moon is read as a lunation turned up a little louder. These are inclinations of tone, nothing more.
In the almanac
The Almanac's Moon panel shows the Moon's current distance from the Earth, how near she is to perigee or apogee, and the date of the next of each — and marks a coming Full or New Moon that falls close to perigee.