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Decan
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Decan
The decans (/ˈdɛkənz/; Ancient Egyptian: 𓅡𓎡𓏏𓁐𓅱𓏼, romanized: bꜣkt.w, lit. '[those] connected with work') are 36 groups of stars (small constellations) 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" (Greek hōra) of the night for the ancient Egyptians, and they were used as a nocturnal (sidereal clock) beginning by at least the Ninth or Tenth Dynasty of Egypt in the 21st century BC.
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 Greeks called them dekanói (Koine Greek: δεκανοί; pl. of δεκανός dekanós) or "tenths".
Decans gave way to a lunar division of 27 or 28 lunar stations, also known as manzil (Arabic: مَنْزِل), lunar stations, or nakshatras and thence to a zodiac of twelve signs, based on an anthropomorphic pattern of constellations, and their use can be seen in the Dendera zodiac dated to circa 50 BCE.
Decans first appeared in the First Intermediate Period of Egypt on coffin lids. The sequence of these star patterns began with Sirius ("Sothis"), and each decan contained a set of stars and corresponding divinities. As measures of time, the rising and setting of decans marked 'hours' and groups of ten days, which comprised an Egyptian year. The Book of Nut covers the subject of the decans.
There were 36 decans (36 × 10 = 360 days), plus five added days to compose the 365 days of a solar-based year. Decans measure sidereal time and the solar year is six hours longer; the Sothic and solar years in the Egyptian calendar realign every 1460 years. Decans represented on coffins from later dynasties, such as Pharaoh Seti I (d. 1279 BCE), compared with earlier decan images, demonstrate the Sothic cycle shift.
According to Sarah Symons,
Although we know the names of the decans, and in some cases can translate the names (ḥry-ỉb wỉꜣ means 'in the centre of the boat') the locations of the decanal stars and their relationships to modern star names and constellations are not known. This is due to many factors, but key problems are the uncertainty surrounding the observation methods used to develop and populate the diagonal star tables, and the criteria used to select decans (brightness, position, relationship with other stars, and so on).
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.
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Decan
The decans (/ˈdɛkənz/; Ancient Egyptian: 𓅡𓎡𓏏𓁐𓅱𓏼, romanized: bꜣkt.w, lit. '[those] connected with work') are 36 groups of stars (small constellations) 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" (Greek hōra) of the night for the ancient Egyptians, and they were used as a nocturnal (sidereal clock) beginning by at least the Ninth or Tenth Dynasty of Egypt in the 21st century BC.
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 Greeks called them dekanói (Koine Greek: δεκανοί; pl. of δεκανός dekanós) or "tenths".
Decans gave way to a lunar division of 27 or 28 lunar stations, also known as manzil (Arabic: مَنْزِل), lunar stations, or nakshatras and thence to a zodiac of twelve signs, based on an anthropomorphic pattern of constellations, and their use can be seen in the Dendera zodiac dated to circa 50 BCE.
Decans first appeared in the First Intermediate Period of Egypt on coffin lids. The sequence of these star patterns began with Sirius ("Sothis"), and each decan contained a set of stars and corresponding divinities. As measures of time, the rising and setting of decans marked 'hours' and groups of ten days, which comprised an Egyptian year. The Book of Nut covers the subject of the decans.
There were 36 decans (36 × 10 = 360 days), plus five added days to compose the 365 days of a solar-based year. Decans measure sidereal time and the solar year is six hours longer; the Sothic and solar years in the Egyptian calendar realign every 1460 years. Decans represented on coffins from later dynasties, such as Pharaoh Seti I (d. 1279 BCE), compared with earlier decan images, demonstrate the Sothic cycle shift.
According to Sarah Symons,
Although we know the names of the decans, and in some cases can translate the names (ḥry-ỉb wỉꜣ means 'in the centre of the boat') the locations of the decanal stars and their relationships to modern star names and constellations are not known. This is due to many factors, but key problems are the uncertainty surrounding the observation methods used to develop and populate the diagonal star tables, and the criteria used to select decans (brightness, position, relationship with other stars, and so on).
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.
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