Decans (Babylonian Context)

Definition

Decans are thirty-six ten-degree slices of the ecliptic. The system began in Egypt, where 36 stars served as a star-clock: from the Pyramid-Texts era through the New-Kingdom diagonal star clocks, the stars' successive first risings paced the ten-day Egyptian week. The decans entered Mesopotamian and Hellenistic astrology through the Greco-Egyptian transmission of the late Hellenistic period, where they were laid over the twelve-sign zodiac as three "faces" per sign, ten degrees each.

In Tradition

In the Babylonian-Hellenistic-Hermetic transmission, the decans are understood as star-markers of Egyptian origin that were absorbed into the Greco-Egyptian zodiac during the Hellenistic synthesis. Rochberg and Hunger & Pingree document that no decanal scheme is native to Babylonian astronomy itself; the Babylonian contribution was the twelve-sign zodiac onto which the Egyptian decans were grafted. *Liber Hermetis* Chapter I and the Greek-Egyptian magical papyri preserve the Hermetic version, in which each decan has a deity.

In Practice

You can tie each ten-degree segment either to a planet that rules its face — using the Chaldean order, so Mars, Sun, Venus from 0° Aries onward — or to one of the 36 Egyptian decan-deities in the Hermetic and magical tradition. In assessing a planet's essential dignity, the faces count as a minor dignity within the medieval Latin five-fold scheme. In medical and talismanic practice (*Liber Hermetis*, *Picatrix*), each decan governs particular body parts, plants, and image-magic operations. The Egyptian decans are also the raw material of the diagonal star clocks and of the northern-and-southern celestial panels in the tombs of Senmut and Seti I, where they served as time-markers rather than as subdivisions of the zodiac.

Historical Origin

Egyptian decanal practice is documented in the Pyramid Texts and in the Senmut tomb-ceiling celestial diagram (1500-1450 BCE), per Neugebauer & Parker, *Egyptian Astronomical Texts* Volumes I-III (1960-1969). Their adoption into Babylonian-Hellenistic astrology appears in *Liber Hermetis* Chapter I (a 4th-c. CE Latin redaction; Zoller's 2002 translation), in Vettius Valens' *Anthologiae*, and in the Greek-Egyptian magical papyri. Rochberg (*The Heavenly Writing*, 2004) documents the Babylonian zodiac as the frame that received them.

Further Reading

  • Otto Neugebauer & Richard A. Parker, Egyptian Astronomical Texts (EAT) Vol I-III
  • Robert Zoller, The Liber Hermetis Translation
  • Francesca Rochberg, The Heavenly Writing