What is "decans"

The decans (; Egyptian bakiu) are 36 groups of stars (small constellations) used in the Ancient Egyptian astronomy. They rose consecutively on the horizon throughout each earth rotation. The rising of each decan marked the beginning of a new decanal "hour" (Greek hōra) of the night for the ancient Egyptians, and they were used as a sidereal star clock beginning by at least the 9th or 10th Dynasty (c. 2100 BCE).

Because a new decan also appears heliacally every ten days (that is, every ten days, a new decanic star group reappears in the eastern sky at dawn right before the Sun rises, after a period of being obscured by the Sun's light), the ancient Greeks called them dekanoi (δεκανοί; pl. of δεκανός dekanos) or "tenths" (and when the concept of decans reached northern India, they were called drekkana in Sanskrit.)

Decans continued to be used throughout the Renaissance in astrology and in magic, but modern astrologers almost entirely ignore them.