Decan

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.

As measures of time, the rising and setting of decans marked 'hours' and groups of 10 days which comprised an Egyptian year.

[6]These predictable heliacal re-appearances by the decans were eventually used by the Egyptians to mark the divisions of their annual solar calendar.

[7] 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).

[16] The first original decan position due to the precession in ancient times started at 0° of Cancer when the heliacal rising of Sirius (Egyptian Sepdet; Greco-Egyptian: Sothis) before sunrise marking the Egyptian New Year which fell at 0° of Leo at July 20 in the Julian calendar, that is July 22/23 on the Gregorian calendar.

[citation needed] In India, the division of the zodiac into 36 ten degree portions is called either the drekkana (drekkāṇa), the dreshkana (dreṣkāṇa), or the drikana (dṛkāṇa).

'Diagonal star table' from the late 11th Dynasty coffin lid; found at Asyut , Egypt. Roemer- und Pelizaeus-Museum Hildesheim
Astronomical ceiling of Senemut Tomb showing various decans, as well as the personified representations of stars and constellations