What is a decan?
A decan is one third of a sign. Each sign covers 30 degrees of the Sun’s yearly path, so it splits into three 10-degree parts. Astrologers say each part borrows a flavour from a sign of the same element: a second-decan Scorpio carries a touch of Pisces, a third-decan Scorpio a touch of Cancer.
Ten degrees at a time
Each sign is 30° of the ecliptic, and astrologers cut it into three slices of 10°. The Sun spends roughly ten days in each, so a decan is also a stretch of about ten days of the year. Thirty-six decans fill the zodiac. The Latin name for them, facies, gives the other English word: faces. 1,2
Two ways to give a decan its flavour
The older system hands each decan to a planet, running in the so-called Chaldean order (Saturn, Jupiter, Mars, the Sun, Venus, Mercury, the Moon) from the first decan of Aries onwards. The 4th-century astrologer Firmicus Maternus thought a planet in its own decan almost as strong as a planet in its own sign. 1
The more common modern system, popular in the 20th century, gives each decan to a sign of the same element. The first decan of a sign belongs to the sign itself, the second to the next sign of its element, the third to the last. For Scorpio, a water sign, that means Scorpio, then Pisces, then Cancer. This is the version most sun-sign books use, and the one the machine follows.
Where decans come from
Decans are Egyptian before they are astrological. Egyptian star tables painted inside coffin lids, mostly from about 2100 BCE, list 36 stars or star groups, one heading each ten-day week of the civil calendar, and use their risings to tell the hours of the night. The Greek word dekanoi, from deka, ten, was later given to them. 3
When Greek astrologers in Egypt combined the Babylonian zodiac with Egyptian star lore, the 36 decans were folded into the twelve signs, three to a sign. 1,4
How the machine works it out
Calculated facts only, worked out the same way the machine does it.
- The machine reads the Sun's position at noon UTC on your birth date.
- Degrees 0–10 of the sign are the first decan (the sign's own flavour), 10–20 the second (the next sign of the same element), and 20–30 the third (the last sign of that element).
- Each decan lasts about ten days of the calendar.
Where the idea comes from
Era by era, with sources. More in the Reading Room.
- Ancientc. 2100 BCEEgyptian coffin lids from the Middle Kingdom carry diagonal star tables of 36 decans, one for each ten-day week. 3
- Classical1st century BCEHellenistic astrology in Egypt merges the decans with the zodiac signs, three to a sign. 4,1
- Classical4th century CEFirmicus Maternus gives the planetary faces great weight in reading a chart. 1
- Modern20th centurySun-sign books popularise the element-based decans: each sign split into its own, its next and its last sign of the same element.
Common misconceptions
“Decans are a modern refinement of sun signs.” They are older than the zodiac signs themselves, going back to Egyptian star clocks. 3
“There is only one decan system.” Traditional astrology uses planetary faces in the Chaldean order; modern sun-sign astrology uses the element system. They give different answers. 1
Questions people ask
How do I find my decan?
You need the degree of your Sun. Under 10° is the first decan, 10–20° the second, 20–30° the third.
Are decans the same as cusps?
No. A cusp is the boundary between signs (or houses); a decan is a third of a sign.
Why 36?
Twelve signs times three, and, earlier, the Egyptian year of 36 ten-day weeks plus five extra days. 3
Sources
- Faces, Skyscript, Glossary of Astrological Terms (Deborah Houlding). Read on .
- Decans, Skyscript, Glossary of Astrological Terms (Deborah Houlding). Read on .
- Decoding the Star Charts of Ancient Egypt, Scientific American, 1 October 2015 (Sarah Symons and Elizabeth Tasker). Read on .
- Whole Sign Houses, The Astrology Podcast (Chris Brennan), lecture slides. Read on .