The term "week" is sometimes expanded to refer to other time units comprising a few days. Such "weeks" of between four and ten days have been used historically in various places. Intervals longer than 10 days are not usually termed "weeks" as they are closer in length to the fortnight or the month than to the seven-day week.
The English word week comes from the Old English wice, ultimately from a Common Germanic *wikōn-, from a root *wik- "turn, move, change". The Germanic word probably had a wider meaning prior to the adoption of the Roman calendar, perhaps "succession series", as suggested by Gothic wikō translating taxis "order" in Luke 1:8.
Seven-day week 
Evidence of continuous use of a seven-day week appears with the Jews during the Babylonian Captivity of the 6th century BC. Both Judaism (based on the Creation narrative in the Bible) and ancient Babylonian religions used a seven-day week.
Systems derived from the seven-day week 
Soviet Union 
Between 1929 and 1931 the USSR changed from the seven-day week to a five-day week. There were 72 weeks and an additional five national holidays inserted within three of them totaling a year of 365 days.
In 1931, after its brief experiment with a five-day week, the Soviet Union changed to a six-day week. Every sixth day (6th, 12th, 18th, 24th and 30th) of the Gregorian Calendar was a state rest day. The five additional national holidays in the earlier five-day week remained and did not fall on the state rest day. But as January, March, May, July, August, October and December have 31 days, the week after the state rest day of the 30th was seven days long (31st–7th). This extra day was a working day for most or an extra holiday for others. Also as February is only 28 or 29 days depending on whether it is a leap year or not, the first of March was also made a state rest day, although not every enterprise conformed to this. To clarify, the week after the state rest day, 24/25 February to 1 March, was only five or six days long, depending on whether it was a leap year or not. The week after that, 2 to 6 March, was only five days long.
The calendar was abandoned 26 June 1940 and the seven-day week reintroduced the next day.
Decimal calendar 
A 10-day week, called décade, was used in France for nine and a half years from October 1793 to April 1802; furthermore, the Paris Commune adopted the Revolutionary Calendar for 18 days in 1871.
Christian "eighth day" 
For early Christians, Sunday, as well as being the first day of the week, was also the spiritual eighth day, as it symbolised the new world created after Christ's resurrection. The concept of the eighth day was symbolic only and had no effect on the use of the seven-day week for calendar purposes. Justin Martyr wrote: "the first day after the Sabbath, remaining the first of all the days, is called, however, the eighth, according to the number of all the days of the cycle, and [yet] remains the first". This does not set up an eight-day week, since the eighth day is also considered to be the first day of the next cycle (i.e., not the following day).
A period of eight days, starting and ending on a Sunday or starting on a major feast day and finishing on the same day of the week a (seven-day) week later, is called an octave. For centuries these were a major feature of the liturgical calendar, particularly of the Catholic Church, and some are still observed, though the number of such octaves has now been radically reduced. Some modern churches uses also preserve the idea of an eight-day period, starting and finishing on the same day of the week, and retain the name "octave" for them; for example, many churches observe an annual "Octave of Prayer for Christian Unity" on 18–25 January or in the week that begins with Pentecost Sunday. Organizations such as 8th Day Center for Justice, based out of Chicago, Illinois, use the concept in terms of social justice as well.
Hermetic lunar week 
The Hermetic Lunar Week Calendar is one of many proposed reforms to the Gregorian Calendar. The lunation is divided into the four moon phases and has six, seven, eight, or nine days depending on the actual time difference between the full moon, first quarter, new moon and last quarter.
"Weeks" in other calendars 
Periods termed "weeks" in calendars unrelated to the Judeo-Christian tradition.
- astelehena ("week-first", Monday)
- asteartea ("week-between", Tuesday)
- asteazkena ("week-last", Wednesday)
The Javanese people of Indonesia have a five-day week known as the Pasaran cycle. This is still in use today and superimposed with seven-day week of the Gregorian calendar and Islamic calendar to become what is known as the 35-day Wetonan Cycle.
The Akan people of West Africa have a 42-day cycle known as Adaduanan. The Adaduanan cycle appears to be based on an older six-day week, still extant in some northern Guan communities such as the Nchumuru, on which is superimposed a seven-day week which may have been brought south with itinerant traders from the Savannah. The six-day week is referred to as Nanson (literally seven-days), reflecting an inclusive numbering system.
Nundinal cycle 
The ancient Etruscans developed an eight-day market week known as the nundinal cycle around the 8th or 7th century BC. This was passed on to the Romans no later than the 6th century BC. As Rome expanded, it encountered the seven-day week and for a time attempted to include both. The popularity of the seven-day rhythm won and the eight-day week disappeared.
The cycle of seven days, named after the sun, the moon, and the five planets visible to the naked eye, was already customary in the time of Justin Martyr, who wrote of the Christians meeting on the Day of the Sun (Sunday).
With regards to measuring time, the Celts regarded darkness as taking precedence over light, so used periods of darkness such as night and winter to begin their calculations of time. This meant that the first period of time in a "week" was a night, followed by a day. Further, they also counted the ending night period, giving rise to periods of time with more nights than days. In Irish, the term nómad is used to signify a small number of days and is exactly the length of the nine night week as in co cend nomaide - a period of time with nine nights bracketing eight days. The nine nights divided nicely into a sidereal month of 27 nights. In Welsh a similar word wythnos meaning "a week" literally means "an eight-night" since it started and ended with a period of night bracketing seven days. Similarly a fortnight pythewnos means "a fifteen night".
Baltic calendars 
Similarly in Latvia petroglyphs were found in 1987, which are considered to show nine-day calendar with three weeks in a month.
Medieval Welsh Calendars 
Although the modern Welsh word for week refers to "eight nights", the Laws of Hywel Dda (in editions surviving from the 12th and 13th centuries) make repeated references to periods of nine days, instead, his month appearing to consist of three 'weeks' and a day.
China, Japan, Korea 
The Chinese ten-day week went as far back as the Xia Dynasty (2070–1600 BC). The law in the Han Dynasty (206 BC – AD 220) required officials of the empire to rest every five days, called mu (沐), while it was changed into 10 days in the Tang Dynasty (AD 618 – 907), called huan or xún (旬). Months were almost three weeks long (alternating 29 and 30 days to keep in line with the lunation). The weeks were labelled shàng xún (上旬), zhōng xún (中旬), and xià xún (下旬) which mean roughly "upper", "middle" and "lower" week.
Markets in Japan followed the Chinese jun (旬) system; see Japanese calendar. In Korea, it was called "Sun" (순,旬).
Ancient Egypt had a ten-day week, three weeks per month with five extra days at the end of the year.
Revolutionary France 
In the French Republican Calendar, each month consisted of three ten-day weeks, called décades.
Other calendar intervals 
The Aztecs divided a solar year of 365 days, Xiuhpohualli, into 18 periods of 20 days and five nameless days known as Nemontemi. Although some call this 20-day division or grouping a month, it has no relation to a lunation and therefore the word "week" is more appropriate.
The Maya also divided the year, Haab', into 18 periods of 20 days, Uinal, and five nameless days known as Wayeb'.
Bali, Indonesia 
The Pawukon is a 210-day calendar consisting of 10 different concurrent weeks of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 days.
- OED s.v. "week n.", entry 1.c.: "Sometimes applied transf. to other artificial cycles of a few days that have been employed by various peoples"
- Senn, Frank C. (1997). Christian Liturgy: Catholic and Evangelical. Fortress Press. ISBN 0-8006-2726-1, 9780800627263 Check
- Pinches, T.G. (2003). "Sabbath (Babylonian)". In Hastings, James. Encyclopedia of Religion and Ethics 20. Selbie, John A., contrib. Kessinger Publishing. pp. 889–891. ISBN 978-0-7661-3698-4. Retrieved 2009-03-17.
- Dialogue with Trypho, chapter XLI
- Meyer, Peter (2005-02-21). "Hermetic Lunar Week Calendar". Hermetic Systems. Retrieved 2009-01-21.
- Astronomy and Basque Language, Henrike Knörr, Oxford VI and SEAC 99 "Astronomy and Cultural Diversity", La Laguna, June 1999. It references Alessandro Bausani, 1982, The prehistoric Basque week of three days: archaeoastronomical notes, The Bulletin of the Center for Archaeoastronomy (Maryland), v. 2, 16-22.
- Bartle, Philip F.W. (1978). "Forty Days: The Akan Calendar". Africa: Journal of the International African Institute (Edinburgh University Press) 48 (1): 80–84. doi:10.2307/1158712. JSTOR 1158712. Retrieved 2009-01-21.
- Apology, chapter LXVII
- Zerubavel, Eviatar (1989). The Seven Day Circle: The History and Meaning of the Week. University of Chicago Press. ISBN 0-226-98165-7, 9780226981659 Check
- Rhys (1840-1915), Sir John (1892). Lectures on the Origin and Growth of Religion as Illustrated by Celtic Heathendom. pp. 360–382.
- The Welsh people: chapters on their origin, history, laws, language ... - Sir John Rhys, Sir David Brynmor Jones - Google Books. p. 220. Retrieved 2012-10-22.
- Gusev, M. (1865). The Ancient Lithuanian Calendar (in Russian) 5. St. Petersburg: Izvestia of the Imperial Archaeological Society. p. 335.
- Straižys, Vytautas; Klimka, Libertas. "Natural rythms and calendar". Cosmology of the Ancient Balts. Global Lithuanian Net. Retrieved 2009-01-21.
- Wade-Evans, Arthur. Welsh Medieval Laws. Oxford Univ., 1909. Accessed 31 Jan. 2013.
- 海, 上 (2005). 《中國人的歲時文化》. 岳麓書社. p. 195. ISBN 7-80665-620-0.
Further reading 
- Colson, Francis Henry (1926). The Week: An Essay on the Origin and Development of the Seven-day Cycle. Cambridge University Press. OCLC 59110177.
|Wikimedia Commons has media related to: Week|
- Englisc Rímbóc: The Anglo-Saxon Calendar
- Chisholm, Hugh, ed. (1911). "week". Encyclopædia Britannica (11th ed.). Cambridge University Press.
- The power of seven, The Economist, 20 December 2001.