The decans (; Egyptian ''bꜣktw'' or ''baktiu'', " hoseconnected with work") are 36 groups of stars (small

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

s) used in the

ancient Egyptian astronomy Egyptian astronomy began in prehistoric times, in the Predynastic Period. In the 5th millennium BCE, the stone circles at Nabta Playa may have made use of astronomical alignments. By the time the historical Dynastic Period began in the 3rd mil ...

to conveniently divide the 360 degree ecliptic into 36 parts of 10 degrees each, both for theurgical and heliacal

horological Horology (; related to Latin '; ; , interfix ''-o-'', and suffix ''-logy''), . is the study of the measurement of time. Clocks, watches, clockwork, sundials, hourglasses, clepsydras, timers, time recorders, marine chronometers, and atomic clo ...

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 An hour (symbol: h; also abbreviated hr) is a unit of time conventionally reckoned as of a day and scientifically reckoned between 3,599 and 3,601 seconds, depending on the speed of Earth's rotation. There are 60 minutes in an hour, and 24 ho ...

" (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 station Often called lunar mansion, a lunar station or lunar house is a segment of the ecliptic through which the Moon passes in its orbit around the Earth. The concept was used by several ancient cultures as part of their calendrical system. Stations ...

s, also known as ''manzil'', lunar mansions or

nakshatras Nakshatra ( sa, नक्षत्रम्, translit=Nakṣatram) is the term for lunar mansion in Hindu astrology and Indian Astronomy. A nakshatra is one of 27 (sometimes also 28) sectors along the ecliptic. Their names are related to a ...

and thence to a

zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the Sun path, apparent path of the Sun across the celestial sphere over the course of the year. ...

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.

Ancient Egyptian origins

Astronomical Ceiling, Tomb of Senenmut MET DT207429

Decans first appeared in the 10th Dynasty (2100 BCE) on coffin lids. The sequence of these star patterns began with Sothis (

Sirius Sirius is the list of brightest stars, brightest star in the night sky. Its name is derived from the Ancient Greek language, Greek word , or , meaning 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinisation ...

), 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 10 days which comprised an Egyptian year. The ancient ''

Book of Nut The ''Book of Nut'' (original title: ''The Fundamentals of the Course of the Stars'') is a collection of ancient Egyptian astronomical texts, also covering various mythological subjects. These texts focus on the cycles of the stars of the decan ...

'' 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 Sidereal time (as a unit also sidereal day or sidereal rotation period) (sidereal ) is a timekeeping system that astronomers use to locate celestial objects. Using sidereal time, it is possible to easily point a telescope to the proper coord ...

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 King

Seti I Menmaatre Seti I (or Sethos I in Greek) was the second pharaoh of the Nineteenth Dynasty of Egypt during the New Kingdom period, ruling c.1294 or 1290 BC to 1279 BC. He was the son of Ramesses I and Sitre, and the father of Ramesses II. The ...

) compared with earlier decan images demonstrate the Sothic-solar 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).

Later developments

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

calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day within such a system. A calendar is also a physi ...

. Thus the heliacal rising of

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 Hellenistic astrology is a tradition of horoscopic astrology that was developed and practiced in the late Hellenistic period in and around the Mediterranean Basin region, especially in Egypt. The texts and technical terminology of this tradition o ...

arose in Alexandria, recorded principally in the work of Claudius

Ptolemy Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importanc ...

and

Vettius Valens Vettius Valens (120 – c. 175) was a 2nd-century Hellenistic astrologer, a somewhat younger contemporary of Claudius Ptolemy. Valens' major work is the ''Anthology'' ( la, Anthologia), ten volumes in Greek written roughly within the period 150 t ...

, various systems attributing symbolic significance to decans arose and linked these to the "wandering stars" and the "Lights": the Sun, Moon, Mercury Venus, Mars as well as Jupiter and Saturn. 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) In astrology, a ''decan'' is the subdivision of a sign. In order to give fuller interpretation to the zodiac signs, ancient astrologers subdivided each sign into periods of approximately ten days. These divisions are known as the "decans" or "de ...

); and correlated with astrological signs.

Descriptions of the decans

Decans are named in various Greco-Egyptian sources, many

Hermetic Hermetic or related forms may refer to: * of or related to the ancient Greek Olympian god Hermes * of or related to Hermes Trismegistus, a legendary Hellenistic figure based on the Greek god Hermes and the Egyptian god Thoth ** , the ancient and m ...

writings, the

Testament of Solomon The Testament of Solomon is a pseudepigraphical composite text ascribed to King Solomon but not regarded as canonical scripture by Jews or Christian groups. It was written in the Greek language, based on precedents dating back to the early 1st mil ...

,''Dekane und Dekansterbilder'' by Wilhelm Gundel, pub. J.J. Augustin, Glückstadt und Hamburg, 1936, p.77-81 and the writings of

Aristobulus of Paneas Aristobulus of Alexandria ( el, Ἀριστόβουλος) also called Aristobulus the Peripatetic () and once believed to be Aristobulus of Paneas, was a Hellenistic Jewish philosopher of the Peripatetic school, though he also used Platonic a ...

.Gundel, p. 406-408

Julius Firmicus Maternus __NOTOC__ Julius Firmicus Maternus was a Roman Latin writer and astrologer, who received a pagan classical education that made him conversant with Greek; he lived in the reign of Constantine I (306 to 337 AD) and his successors. His triple career m ...

Cosmas of Maiuma Saint Cosmas of Maiuma, also called Cosmas Hagiopolites ("of the Holy City"), Cosmas of Jerusalem, Cosmas the Melodist, or Cosmas the Poet (d. 773 or 794), was a bishop and an important hymnographer in the East. He is venerated as a saint by th ...

Joseph Justus Scaliger Joseph Justus Scaliger (; 5 August 1540 – 21 January 1609) was a French Calvinist religious leader and scholar, known for expanding the notion of classical history from Greek and Ancient Roman history to include Persian, Babylonian, Jewish an ...

, and

Athanasius Kircher Athanasius Kircher (2 May 1602 – 27 November 1680) was a German Jesuit scholar and polymath A polymath ( el, πολυμαθής, , "having learned much"; la, homo universalis, "universal human") is an individual whose knowledge spans ...

. Images of the decans are described in Hermetic writings, by the Indian astrologer

Varāhamihira Varāhamihira ( 505 – 587), also called Varāha or Mihira, was an ancient Indian astrologer, astronomer, and polymath who lived in Ujjain (Madhya Pradesh, India). He was born at Kapitba in a Brahmin family, in the Avanti region, roughly co ...

, in the

Picatrix ''Picatrix'' is the Latin name used today for a 400-page book of magic and astrology originally written in Arabic under the title ''Ghāyat al-Ḥakīm'' ( ar, غاية الحكيم), which most scholars assume was originally written in the midd ...

, and in Japanese writings.Gundel, p.223-225 Varāhamihira's images of the decans was influenced by Greco-Egyptian, if not Hermetic, depictions of the decans by way of the

Yavanajataka The Yavanajātaka (Sanskrit: ''yavana'' 'Greek' + ''jātaka'' ' nativity' = 'nativity according to the Greeks'), written by Sphujidhvaja, is an ancient text in Indian astrology. According to David Pingree, it is a later versification of an earl ...

."The Indian Iconography of the Decans and Horâs" by David Pingree, ''Journal of the Warburg and Courtauld Institutes'', vol. 26, no. 3/4 (1963), p. 223-254 Their role in Japanese astrology may have derived from an earlier ChineseGundel, p. 217-221 or Indian form"Bukkyō tenbugaku-senseijutsu no zuzō gakuteki junmen: sanjū rokkin to Dekan" by Yano Michio, ''Dōshisha daigaku rikō kenkyū hōkoku'', 48, no 4 (2008), 1-6. possibly from adding the twelve animals of the

Chinese zodiac The Chinese zodiac is a traditional classification scheme based on the lunar calendar that assigns an animal and its reputed attributes to each year in a repeating twelve-year cycle. Originating from China, the zodiac and its variations remain ...

to a list of twenty-four hour stars. They were most common between the

Kamakura is a city in Kanagawa Prefecture, Japan. Kamakura has an estimated population of 172,929 (1 September 2020) and a population density of 4,359 persons per km² over the total area of . Kamakura was designated as a city on 3 November 1939. Kamak ...

and

Edo period The or is the period between 1603 and 1867 in the history of Japan, when Japan was under the rule of the Tokugawa shogunate and the country's 300 regional '' daimyo''. Emerging from the chaos of the Sengoku period, the Edo period was characteriz ...

s. 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) on sunset like Jewish and Islamic calendars marking the Egyptian New Year and now the 1st decan falls on 0° of Leo at July 20 in the Julian calendar, that is July 22/23 on the Gregorian calendar.

Ancient India

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). The iconography and use of the drekkanas is mention earliest by

Sphujidhvaja The Yavanajātaka (Sanskrit: ''yavana'' 'Greek' + ''jātaka'' ' nativity' = 'nativity according to the Greeks'), written by Sphujidhvaja, is an ancient text in Indian astrology. According to David Pingree, it is a later versification of an earl ...

(269–270 CE), and given detailed treatment by Varahamihira in his Brihat-Samhita (550 CE). Modern scholars believe the decans were imported into India through the Greeks, who learned about them from the Egyptians.

Footnotes

References

External links

Ancient Egyptian Astronomy Database
(Symons, Cockcroft, Bettencourt & Koykka, 2013)

Asterisms (astronomy) Constellations Ancient astronomy Technical factors of Chinese astrology Technical factors of Western astrology Egyptian calendar