Decan

Definition

A decan is a 10-degree slice of a zodiac sign. Each sign holds three of them, so there are 36 decans around the whole zodiac. Every decan has its own planetary ruler, which lets astrologers read a placement more finely than the sign alone allows. The system began in ancient Egypt as a star-based scheme of 36 ten-day units — decadal stars that marked ten-day weeks — and was later absorbed into Hellenistic astrology, where each decan was given a ruler following the Chaldean planetary order (which puts Mars over the first decan of Aries).

In Tradition

In both the Egyptian decadal-star tradition and its Hellenistic adaptation, the decan is a 10-degree zone of minor dignity that modifies the sign-level reading. In Hellenistic doctrine the decan ruler acts as a third-tier dispositor — a ruler that "manages" a planet — ranking below the domicile lord and the bound (or term) lord. The medieval Arabic-Latin tradition carried the decan imagery, the per-decan pictures, into magical-astrological practice, attested in the Picatrix and in the Hermes texts adjacent to the 15 Behenian stars.

In Practice

To find a planet's decan, astrologers divide its degree within the sign by 10 and take the whole number: degrees 0–9 give the first decan, 10–19 the second, 20–29 the third. They then consult the Chaldean-order decan-ruler table — the first decan of Aries is ruled by Mars, the second by the Sun, the third by Venus, and the cycle runs on through Mercury, Moon, Saturn, and Jupiter, coming back to Mars at the first decan of Cancer. Decan rulership counts as a minor dignity that strengthens a planet expressing itself in its own decan, and it adds the decan ruler's flavour to other placements. Modern Western practitioners, such as Austin Coppock in 36 Faces, revive the decanic-image tradition for psychological and symbolic work.

Historical Origin

Decans are attested in Egyptian primary sources from the Old Kingdom — the Senenmut tomb ceiling, the Seti I cenotaph, the Ramesseum, and Tanis — as 36 decadal-star groups whose heliacal rising marked ten-day intervals of the civil calendar. Holden's history documents how Hellenistic astrology absorbed them through Hermetic and Pseudo-Manetho material; Bram's edition of the Mathesis preserves the systematization by Firmicus. Greenbaum's Daimon gives the Greek derivation of dekanos. The Yavanajataka carried the system to India in the 2nd–3rd century CE.

Etymology

Origin: Greek/Egyptian. Meaning: Ruler of ten.

Further Reading

• James H. Holden, A History of Horoscopic Astrology
• Firmicus Maternus, Mathesis (Bram trans.)
• Austin Coppock, 36 Faces