Egyptian Decans

dee-KANZ

Definition

The Egyptian decans are thirty-six stars or small star-groups, each one marking a ten-day stretch of the Egyptian civil year and an hour of the night. This system anchored Egyptian timekeeping from at least the Ninth Dynasty (around 2150 BCE) through the Ptolemaic period. Hellenistic astrology later inherited it: the thirty-six decans became ten-degree slices of the zodiac signs — three decans to a sign — each with its own planetary ruler, image, and interpretive meaning.

In Tradition

Egyptologists read the decans as a calendar-and-observation system built on the ten-day week of the civil year: thirty-six decans times ten days gives 360 days, leaving five extra "epagomenal" days outside the cycle. Used as markers of the night hours — each decan rising in turn across the night — they produced the diagonal star-clocks found on Middle Kingdom coffin lids. The later Hellenistic-Roman reception treats the decans instead as ten-degree slices of each sign, with attached planetary rulers, talisman images, and links to medicine.

In Practice

The Egyptian system needed no chart-casting; its working use was calendrical — scheduling heliacal risings (a star's first dawn reappearance) and festivals — and horological, telling the hours of the night. Astrologers in classical or Renaissance lineages reach the inherited decan system through three channels of transmission: the Hellenistic "faces" (each ten-degree third ruled by a planet in Chaldean order), the decanic images of the Liber Hermetis, and the Renaissance tables of decan stones, herbs, and talismans in the Picatrix and Agrippa. Modern scholarship works from the Clagett, Belmonte-Lull, and Faulkner editions of the primary Egyptian sources.

Historical Origin

The decan system is attested from the Old Kingdom onward; Clagett notes that the ten-day week "dictated the use of 36 decans (stars or groups of stars) in the star clocks." Diagonal star-clocks appear on coffin lids from around 2150 BCE, and the earliest decanal astronomical ceiling is the Senenmut tomb (TT 71, around 1473 BCE). The Hellenistic transmission survives in the Liber Hermetis Trismegisti, in Hephaistio of Thebes, and in Firmicus Maternus (Mathesis IV.22).

Further Reading

  • Marshall Clagett, Ancient Egyptian Science, Volume Two: Calendars, Clocks, and Astronomy
  • Juan Antonio Belmonte and José Lull, In Search of Cosmic Order: Astronomy in Ancient Egypt