Decans

Using the wheel

The first pair of buttons chooses how the decans are ruled, as Chaldean faces or by triplicity; the second chooses whose sky, your birth if a chart is saved on this device or the sky now. Point at a decan, tap it, or focus the wheel and use the arrow keys, and the sentence under the wheel reads it: its degrees, its ruler, its terms and any planet standing in it. At rest it reads the decan the Sun is in. The list below gives every planet’s face, its decan by triplicity and its term together, whichever scheme the wheel is showing.

Thirty-six star groups

The decans began in Egypt as groups of stars that rose one after another through the night, each marking an hour, with a new one taking over about every ten days. When Babylonian and Greek astrology met them in Hellenistic Egypt they were fitted to the zodiac, ten degrees to a decan and three to a sign. Greek writers called them faces and gave each one a planet in the Chaldean order, from the slowest to the fastest: Saturn, Jupiter, Mars, the Sun, Venus, Mercury, the Moon. Starting with Mars at 0° Aries and running round, the order comes back to Mars for both the last decan of Pisces and the first of Aries.

Two ways to rule them, and the terms

The faces are the version the medieval tables score. Many later astrologers, and most modern ones, use the triplicity decans instead: the first ten degrees of a sign belong to its own ruler, and the next two to the rulers of the other signs of its element in zodiac order, so Aries runs Mars, the Sun, Jupiter. The wheel uses the traditional rulers; with the modern ones Pluto stands in for Scorpio, Uranus for Aquarius and Neptune for Pisces wherever those signs lend a ruler. The inner ring is the Egyptian terms as Ptolemy records them: five unequal stretches in every sign, ruled by the five planets and never by the lights. The page checks that each sign’s terms come to thirty degrees before it draws them.

An example

Take a planet at 15° Gemini. It is in the second decan of Gemini, 10° to 20°. As a Chaldean face that decan belongs to Mars: running Saturn, Jupiter, Mars, the Sun, Venus, Mercury and the Moon round from Mars at 0° Aries, the first decan of Gemini, the seventh in all, falls to Jupiter and the second to Mars. By triplicity the same decan belongs to Venus, because Libra is the next air sign after Gemini and Venus rules Libra. Its term is Venus’s too, which in Gemini runs from 12° to 17°. So one degree reads as the face of Mars and as a decan and term of Venus, and the page shows both schemes rather than choosing between them.

Decans by birthday, and other confusions

Magazine columns often split a sign by date, as in “first decan Aries, 21 to 30 March”. That is the triplicity scheme laid on the calendar, and it is only approximate: the Sun moves about a degree a day, so a decan lasts about ten days, but where it starts shifts with the year and the time zone just as sign dates do. A birth near the edge of a decan needs the degree from a chart rather than the date.

The zodiac on this page is the tropical one. Indian astrology also divides each sign in three, the drekkana, and gives the parts by element in the same way, but on the sidereal zodiac, so the same planet can land in a different decan there.

How faces and terms add to rulership, exaltation and triplicity in the old scores is on Dignities, which reads from the same tables as this page. The Chaldean order that deals out the faces also sets the planetary hours on Hours, and the bright stars along the zodiac, where the decans began, are on Fixed stars. The Golden Dawn tied the numbered cards of the tarot’s minor arcana, two to ten, to the faces, so the Two of Wands stands for Mars in Aries; the cards themselves are on Cards.

What it claims

A decan or a term is read in the tradition as a finer shade of its sign, coloured by the planet that rules it, and some writers attached images and descriptions to each face. The page shows the division and where the planets stand in it. It measures positions and predicts nothing.