Three 10° Divisions of Each Sign
Each zodiac sign of 30° is divided into three decanates (decans) of 10° each: the first decan (0°–9°59'), the second decan (10°–19°59'), and the third decan (20°–29°59'). Each decan has a sub-ruler — a planet that adds its flavor to the primary sign's energy. The first decan is purest in the sign's character; the second and third decans bring modifying influences from the other signs of the same element, giving nuance to a planet's placement within the sign.
Decans of Aries (Example)
| Decan | Degrees | Sub-Ruler | Flavor |
|---|---|---|---|
| 1st Decan ♈ | 0°–9°59' | Mars | Pure Aries initiative |
| 2nd Decan ♈ | 10°–19°59' | Sun (Leo decan) | Proud, dramatic Aries |
| 3rd Decan ♈ | 20°–29°59' | Jupiter (Sag decan) | Expansive, philosophical Aries |
Using Decans in Interpretation
Decans add a sub-layer of nuance to any planet's sign placement. A Sun at 22° Taurus falls in the 3rd decan — the Capricorn decan, sub-ruled by Saturn — giving the Taurus Sun a more ambitious, disciplined, and achievement-oriented quality than a first-decan Taurus Sun. Decans are useful for distinguishing between two people with the same Sun sign but different placements within that sign, and for refining interpretation of planetary character. In Hellenistic astrology, decans also carried individual fixed-star associations with distinct appearance and fate descriptions.