Decan
Each sign divided into three 10° sections with sub-rulerships.
Each zodiac sign spans 30° and is divided into three decans (or decanates) of 10° each. Each decan has a sub-ruler that adds nuance to the sign's expression. For example, Aries is sub-ruled by Mars (1st decan), Sun (2nd), and Jupiter (3rd). Understanding your planets' decans adds depth to interpretation - two people with Sun in Aries but in different decans will express it differently.
Example
First decan Aries (0-10°) is the purest Aries energy. Third decan Aries (20-30°) has Sagittarian/Jupiter influence, adding philosophy to the warrior.
Cultural Context
Decans originated in Egypt around 2100 BCE — 36 star groups that rose every 10 days. When Greeks merged Egyptian star knowledge with Mesopotamian zodiac astrology, decans became subdivisions of signs. Different systems assign different rulers; the most common modern system uses signs of the same element.
Famous Example
The 36 decans were depicted on Egyptian coffin lids to guide souls through the afterlife. Each decan had its own god and imagery. Renaissance astrology revived decan imagery, influencing Tarot — the minor arcana pip cards (2-10) correspond to decans.
Did You Know?
Some astrologers use decans to explain why people of the same Sun sign can seem so different. A first-decan Virgo (0-10°) is 'double Virgo' (Mercury-ruled), while a third-decan Virgo (20-30°) has Venus/Taurus influence — more sensual and less cerebral.