The decans (/ˈdɛkənz/; 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). Decans continued to be used throughout the Renaissance in astrology and in magic, but modern astrologers almost entirely ignore them.