Astrolabe Glossary and Notes

Decans

The system of decans was originally associated with thirty-six constellations that rose at specified times of the year. Early examples of such lists can be found on coffin lids from the Egyptian Middle Kingdom and ceilings of tombs dating from the New Kingdom. Evidence suggests that their risings marked both the days of the year and the time of night. As early as 2100 B.C. the decans were associated with particular gods. This system evolved over time and became another scheme for dividing the zodiac.

Like the faces, the decans are even divisions of 10° each, starting with the first point of Aries and terminating at the last point of Pisces. Whereas the faces appear to have been indigenous to Arabic astrology, the system of decans is found first in Egyptian and later in Indian astrology (al- Bīrūnī asserts that the decans were a Hindu practice). By the time al- Bīrūnī wrote his The Book of Instruction in the Elements of the Art of Astrology in the early eleventh century, the decans were ruled not by Egyptian gods but were governed by a planet or luminary. Although the decans spread widely throughout the Islamic and Indian worlds, tables of decans are rare on astrolabes. The lords of the decans are given below.

Zodiacal Sign Planetary Lords
10° 20° 30°
Aries المراخ
Mars
الشمس
Sun
المشترى
Jupiter
Taurus الزهره
Venus
العطارد
Mercury
الوحل
Saturn
Gemini العطارد
Mercury
الزهره
Venus
الوحل
Saturn
Cancer القمر
Moon
المراخ
Mars
المشترى
Jupiter
Leo الشمس
Sun
المشترى
Jupiter
المراخ
Mars
Virgo العطارد
Mercury
الوحل
Saturn
الزهره
Venus
Libra الزهره
Venus
الوحل
Saturn
العطارد
Mercury
Scorpio المراخ
Mars
المشترى
Jupiter
القمر
Moon
Sagittarius المشترى
Jupiter
المراخ
Mars
الشمس
Sun
Capricorn الوحل
Saturn
الزهره
Venus
العطارد
Mercury
Aquarius الوحل
Saturn
العطارد
Mercury
الزهره
Venus
Pisces المشترى
Jupiter
القمر
Moon
المراخ
Mars
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