Древнеегипетская астрономия: Деканы и звёздные группы

Groups of stars in Ancient Egyptian astronomy
decans in ancient astronomy

The decans ('/d//ɛ//k//ən//z/; Egyptian bꜣktw or baktiu, "[those] connected with work") are 36 groups of stars (small constellations) used in the ancient Egyptian astronomy to conveniently divide the 360 degree ecliptic into 36 parts of 10 degrees each, both for theurgical and heliacal horological 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" (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". Decans gave way to a lunar division of 27 or 28 lunar stations, also known as manzil, lunar mansions or nakshatras and thence to a zodiac of 12 signs, based on an anthropomorphic pattern of constellations, and their use can be seen in the Dendera zodiac dated to circa 50 BCE.

These predictable heliacal re appearances by the decans were eventually used by the Egyptians to mark the divisions of their annual solar calendar. Thus the heliacal rising of Sirius marked the annual flooding of the Nile. This method led to a system of 12 daytime hours and 12 nighttime hours, varying in length according to the season. Later, a system of 24 "equinoctial" hours was used. After Hellenistic astrology arose in Alexandria, recorded principally in the work of Claudius Ptolemy and Vettius Valens, various systems attributing symbolic significance to decans arose and linked these to the "wandering stars" (Mercury, Venus, Mars, Jupiter and Saturn) and the "Lights": (Sun and Moon). Decans were connected, for example, with the winds, the four directions, the sect (day or night,) male and female, as well as the four humours (elements;) also these were hermetically considered linked with various diseases and with the timing for the engraving of talismans for curing them; with decanic "faces" (or "phases"), a system where three decans are assigned to each zodiacal sign, each covering 10° of the zodiac, and each ruled by a planetary ruler (see Decan (astrology)); and correlated with astrological signs.

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