Decan

Origin in Egyptian astrology

The decan system (Greek dekanós, "ten") originated in ancient Egypt at least from 2100 BC. The Egyptians divided the night into 36 decans (specific stars or constellations that rose successively throughout the year), one for each 10 days, used for night time measurement and calendrical calculations. From there, Hellenistic and Babylonian astrologers absorbed and integrated the system into their solar zodiac, getting our current decanal system.

Each decan was associated with: a planet ruler (the modern Western system uses Chaldean order: starting in Aries and following the order of the planets in their distance from Earth in the geocentric Ptolemaic system: Mars, Sun, Venus, Mercury, Moon, Saturn, Jupiter, repeating cyclically), a deity (in original Egyptian astrology), specific qualities that nuance the energy of the general sign.

Decans of each sign

Each sign has 3 decans of 10°: 1st decan (0°-10°) ruled by the planetary ruler of the sign itself (e.g.: 1st decan of Aries ruled by Mars). 2nd decan (10°-20°) ruled by the planet of the next same triplicity sign in fire (Sun for the 2nd of Aries, going to the next sign of fire that is Leo). 3rd decan (20°-30°) ruled by the planet of the third sign of the same triplicity (Jupiter for 3rd of Aries, going to Sagittarius).

Practical example: if you are Aries born March 23 (day 0° of Aries), you are in 1st decan, of pure martial energy — initiating, fiery, brave, impulsive, leadership. If you are Aries born April 5 (day 15° of Aries), you are in 2nd decan ruled by Sun — Aries with extra solar energy, more dramatic, magnetic, with leadership but more conscious. If you are Aries born April 18 (day 28° of Aries), you are in 3rd decan ruled by Jupiter — Aries with expansive Jovian energy, more philosophical, lover of distant journeys, expansive teaching. Each decan adds nuance.

Use in modern astrology

Modern Western astrology uses the decans as secondary refinement of natal interpretation: after analysing the sign of each planet, the experienced astrologer also considers in which decan it is for additional precision. The decans are particularly useful for: 1) Understanding why two people of the same sign feel notably different (probably they are in different decans). 2) More precise sub-interpretations of horoscopes. 3) Karmic-Vedic readings (also incorporates similar concept of navamsas or 9-divisions). 4) Esoteric astrology (each decan has additional correspondences with specific images, "decanal genies", etc., elaborate medieval system).