Two people with the Sun in Scorpio can be very different Scorpios. Part of the reason is aspects and houses, but part of it is simply where in Scorpio the Sun sits. Astrologers have been dividing each sign into three 10-degree sections for well over two thousand years, and those sections are called decans.
Decans are one of the oldest layers in the zodiac, older than the twelve signs themselves as a system of time-keeping. They're also one of the most confusing, because there are two quite different ways of assigning rulers to them, and many books use one without mentioning the other. This guide explains where decans come from, how both rulership systems work, and how to use them in a chart without overreaching.
What a decan is
Each sign covers 30 degrees. Divide it into three equal parts and you get:
- First decan: 0 to 10 degrees
- Second decan: 10 to 20 degrees
- Third decan: 20 to 30 degrees
Twelve signs times three gives 36 decans around the full zodiac. A planet at 14 degrees Taurus is in the second decan of Taurus. A planet at 27 degrees Libra is in the third decan of Libra. Degrees count from zero, so 10 degrees 00 minutes exactly is the start of the second decan, not the end of the first.
Each decan has a planetary ruler, and that ruler adds a secondary flavor to anything placed there. The sign is still the main voice. The decan ruler is the accent.
Egyptian origins
Decans began as stars, not zodiac divisions. Ancient Egyptian astronomers tracked a series of 36 stars or star groups that rose on the eastern horizon just before dawn, one after another, each for roughly ten days. Thirty-six ten-day periods gave a 360-day year, with five extra days added to complete the Egyptian civil calendar.
The same stars were used to tell time at night: as each decan star rose in turn over the course of the night, it marked the passing hours. Star tables painted on coffin lids from around 2000 BCE show this system in use. The Egyptian division of the night into twelve hours is generally traced to it.
Much later, in the Hellenistic period, when Babylonian zodiac astrology met Egyptian tradition in Alexandria, the decans were mapped onto the twelve signs, three per sign. They kept associations with specific images and, for some writers, with medicine and talismans. What reached later Western astrology is mainly the rulership scheme, and there are two of those.
The Chaldean system: faces
The older rulership system assigns the seven traditional planets to the decans in Chaldean order, which ranks the planets from slowest to fastest as seen from Earth:
Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon
The sequence starts with Mars at 0 degrees Aries and runs forward through the zodiac, cycling through the seven planets. Thirty-six decans divided among seven planets means the cycle runs five full times plus one, so Mars rules both the first decan of Aries and the last decan of Pisces. In this system the decans are also called faces, and they form the fifth and smallest of the essential dignities.
| Sign | 0 to 10 | 10 to 20 | 20 to 30 |
|---|---|---|---|
| Aries | Mars | Sun | Venus |
| Taurus | Mercury | Moon | Saturn |
| Gemini | Jupiter | Mars | Sun |
| Cancer | Venus | Mercury | Moon |
| Leo | Saturn | Jupiter | Mars |
| Virgo | Sun | Venus | Mercury |
| Libra | Moon | Saturn | Jupiter |
| Scorpio | Mars | Sun | Venus |
| Sagittarius | Mercury | Moon | Saturn |
| Capricorn | Jupiter | Mars | Sun |
| Aquarius | Venus | Mercury | Moon |
| Pisces | Saturn | Jupiter | Mars |
Notice that the face rulers often have little to do with the sign itself. The first decan of Leo is ruled by Saturn, and the second decan of Libra is also Saturn's. That's the point: faces add a second, independent planetary influence. A planet in its own face (the Sun at 15 degrees Aries, Mercury at 25 degrees Virgo) gains a small dignity, worth one point in William Lilly's scoring. See the essential dignities guide for how faces fit with the larger dignities.
The triplicity system
The system most modern Western astrologers use works differently. Each decan is ruled by the planet that rules one of the three signs of the same element, taken in zodiac order:
- First decan: ruled by the sign's own ruler
- Second decan: ruled by the ruler of the next sign in the same element
- Third decan: ruled by the ruler of the third sign in that element
For Aries (fire), the three fire signs in order from Aries are Aries, Leo, and Sagittarius. So the decans are Aries-Mars, Leo-Sun, and Sagittarius-Jupiter. For Leo, start at Leo: Sun, then Jupiter (Sagittarius), then Mars (Aries). For Taurus (earth): Venus, then Mercury (Virgo), then Saturn (Capricorn).
This scheme is also found in Indian astrology, where the same division is called the drekkana. In Western use it's popular because it's easy to remember and stays within the element, so each decan reads as a blend of the sign with a sibling sign. A Sun in the third decan of Aries picks up some Sagittarian breadth. A Sun in the second decan of Cancer picks up some Scorpio depth.
Modern practitioners often plug in the modern rulers here, so the second decan of Cancer is given to Pluto (for Scorpio) and the third to Neptune (for Pisces). Traditional users of the same scheme stick with Mars and Jupiter.
Which system to use
They answer different questions.
Faces (Chaldean) are a dignity. They tell you whether a planet has a small amount of its own authority in that spot, and which planet has a claim over that part of the sign. Use them if you work with traditional dignity tables, almutens, or classical techniques.
Triplicity decans are descriptive. They shade the meaning of a sign by pulling in a sibling sign of the same element. Use them for character description, especially of the Sun, Moon, and Ascendant.
You don't have to pick one forever. Many astrologers use faces for judging strength and triplicity decans for adding color to a description. What you shouldn't do is mix them silently: if you say a placement is "in the Jupiter decan," make sure you know which system you mean. The first decan of Sagittarius is ruled by Mercury in the Chaldean system and by Jupiter in the triplicity system.
How to use decans in a chart
Decans are fine detail. Apply them after you've read sign, house, dignity, and aspects, never before. A practical order:
- Start with the Ascendant, Sun, and Moon. These are where decans add the most noticeable nuance, because they're the points people most identify with.
- Note the decan ruler and find it in the chart. If the decan ruler is strong and well placed, that second influence is easy to see. If it's weak or afflicted, it may be barely perceptible.
- Look for repetition. If your Sun is in a Saturn face and Saturn also aspects your Sun, the Saturn note becomes louder. One faint signal is noise; two pointing the same way is worth mentioning.
- Check the degree carefully. A planet at 9 degrees 58 minutes and one at 10 degrees 02 minutes are in different decans. For fast points like the Ascendant, a few minutes of birth time error can shift the decan.
Worked examples
Sun at 4 degrees Scorpio. Chaldean face: Mars. Triplicity decan: Scorpio's own ruler (Mars traditionally, Pluto in modern usage). Both systems agree on a strong Martian or Plutonian note, so this is a concentrated, direct Scorpio, less diffuse than later degrees.
Moon at 16 degrees Cancer. Chaldean face: Mercury. Triplicity decan: the Scorpio decan (Mars, or Pluto in modern usage). Here the systems diverge. The face points to a Moon that processes emotion through talk and thought. The triplicity decan points to emotional intensity and privacy. Check which of EMercury or Mars is more prominent in the chart before leaning either way.
Ascendant at 23 degrees Libra. Chaldean face: Jupiter. Triplicity decan: the Gemini decan (Mercury). A Libra rising with sociable, talkative, idea-driven presentation, and with Jupiter adding generosity or a touch of formality. If RVenus, the chart ruler, is also in an air sign, the airy side of this rising sign is reinforced.
Venus at 8 degrees Taurus. Chaldean face: Mercury. Triplicity decan: Venus itself, since the first decan belongs to the sign's own ruler. Venus is in domicile and in its own triplicity decan, which just repeats the strength. The Mercury face adds a practical, verbal side to how this person handles pleasure and money.
What decans can't do
Decans won't turn a chart around. A debilitated planet in its own face is still debilitated; the face adds a single point, not a rescue. Nor are they a reliable basis for sun-sign personality types on their own. The popular "which decan are you" descriptions often lean on a single factor that should only ever be one voice among many.
They also depend on accurate degrees. For the outer planets, which stay in one decan for months or years, the decan says more about a generation than a person.
Find your decans
Your chart lists each planet's exact sign and degree. Note the degrees for your Sun, Moon, and Ascendant, place each in its decan, and look up both the Chaldean face and the triplicity ruler. Then check whether those ruling planets are prominent in your chart. If you're newer to the signs, the 12 zodiac signs explained and elements and modalities are the foundations decans are built on.