Decan

The decans are 36 groups of stars used in ancient Egyptian astronomy to conveniently divide the 360 degree ecliptic into 36 parts of 10 degrees each, both for theurgical and heliacal chronometrical purposes. The decans each appeared, geocentrically, to rise consecutively on the horizon throughout each daily Earth rotation. The rising of each decan marked the beginning of a new decanal "hour" of the night for the ancient Egyptians, and they were used as a nocturnal beginning by at least the Ninth or Tenth Dynasty of Egypt in the 21st century BC.

Wikipedia →