Decans
The 36 decans
Each sign divided into three parts of ten degrees. The decans are the oldest subdivision in astrology, older than the way we use the signs themselves, and they are the layer that separates an early Aries from a late one.
What a decan is
A sign covers thirty degrees. Split it into three tens and you have its decans. The system is Egyptian in origin, where the decans were groups of stars used to tell the hours of the night, and it was absorbed into Hellenistic astrology and carried forward from there.
It is the answer to the reasonable objection that everybody born in a month cannot be the same. Your decan depends on the degree of your Sun, which depends on the date, and a first-decan Leo and a third-decan Leo are described quite differently by the tradition.
Two systems that disagree
The older face system runs the seven classical planets in Chaldean order around the whole zodiac, starting with Mars at the first degree of Aries. Because seven does not divide into thirty-six, the pattern never repeats, which is why the column below looks irregular and is not.
The modern decanate system gives each decan to one of the three signs of its own element, beginning with the sign itself. Both are shown throughout. Most of the contradictions you will find elsewhere are two sources using different systems without saying so.
♈ Aries
The whole sign →♉ Taurus
The whole sign →♊ Gemini
The whole sign →♋ Cancer
The whole sign →♌ Leo
The whole sign →♍ Virgo
The whole sign →♎ Libra
The whole sign →♏ Scorpio
The whole sign →♐ Sagittarius
The whole sign →♑ Capricorn
The whole sign →♒ Aquarius
The whole sign →♓ Pisces
The whole sign →Why every decan names a tarot card
The Golden Dawn mapped the 36 decans onto the 36 minor arcana pips, two through ten of each suit, and that mapping is why a Rider-Waite-Smith deck attributes a planet and a sign to those cards at all. The suits follow the elements, and the ranks follow modality: the cardinal sign of each element takes two to four, the fixed sign five to seven, the mutable sign eight to ten.
All 36 attributions here are computed from that rule rather than transcribed, and the test suite asserts them against the deck data on our tarot site. If the two ever disagree, one of them is wrong and the build says so.
Which decan is your Sun in?
It depends on the degree, not the date range alone. The chart is free and gives the exact degree of every planet.
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