Week

A week is a time unit equal to a number of days, now usually seven days. Weeks of between 4 and 20 days have been used historically in various places.
==Three day==
The names of the days of the week (aste) in Guipuscoan Basque point to an earlier three-day week.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.
#asteleena ("week-first", Monday) 
#asteartea ("week-between", Tuesday)
#asteazkena ("week-last", Wednesday)
==Four-day==
The Igbo of Nigeria have a traditional calendar with a 4-day week. This "market week" features prominently in the fiction of Chinua Achebe.
==Five-day==
===Javanese===
The Javanese people of Indonesia have a 5-day week known as the Pasaran cycle. This is still in use today and superimposed with Gregorian calendar and Islamic calendar to become what is known as the Wetonan Cycle.
===Soviet Union===
Between 1929 and 1931, the USSR changed from the 7-day week to a 5-day week. There were 72 weeks and an additional 5 national holidays inserted within 3 of them totaling a year of 365 days.
==Six-day==
 
===Soviet Union===
In 1931 after the Soviet Union's 5-day week they changed to a 6-day week. Every 6th day (6th, 12th, 18th, 24th and 30th) of the Gregorian Calendar was a state rest day. The 5 additional national holidays in the earlier 5 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 7 days long (31st-7th). This extra day was a working day for most or extra holiday for others. 
Also as February is only 28 or 29 days depending if a leap year or not, the 1st 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 5 or 6 days long, depending if a leap year or not. The week after that, 2 to 6 March, was only 5 days long.
The calendar was abandoned 26 June 1940 and the 7-day week reintroduced the day after.
===Akan===
The Akan people 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) and reflects the lack of zero in the numbering systems; the last day and the first day are both included when counting the days of a week.
==Seven-day==
The earliest evidence of continuous use of a seven-day week appears with the Jews during the Babylonian Captivity in 586 BCE.
==Eight-day==
===Etruscans (and Romans)===
The ancient Etruscans developed an 8-day market week known as the nundinal cycle around the 8th or 7th century BCE. This was passed on to the Romans no later than the 6th century BCE. As Rome expanded it encountered the 7-day week and for a time attempted to include both. The popularity of the 7-day rhythm won and the 8-day week disappeared forever.
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).Apology, chapter LXVII
Emperor Constantine eventually established the 7-day week in the Roman calendar and in 321 CE.
===Celts===
It is believed the Celtic people used a nine-night week. The moon was used to measure one day from another so nights were more significant. The 9 nights divided nicely into a Sidereal Month of 27 nights. Each week of 9 nights had 8 days. There was also a half week of 5 nights and 4 days.
===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".Dialogue with Trypho, chapter XLI This does not set up an 8-day week, since the eighth day, not the following day, is considered to be also the first of a cycle.
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 (7-day) week later, is called an octave. For centuries these were a major feature of the liturgical calendar, particularly of the Roman Catholic Church, and some are still observed, though the number of such octaves has now been radically reduced. Some modern Church 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.
==Nine-day==
===Lithuanian===
In the 14th century, the Grand Duchy of Lithuania used a solar-lunar calendar. The structure of this calendar was understood with the help of the so-called Gediminas Sceptre discovered in 1680 
===Ancient Balts===
Historical records give evidence that the week of ancient Balts was nine-days long. Thus, the sidereal month must have been divided into three parts.
==Ten-day==
===China===
The Chinese 10 day week went as far back as the Shang Dynasty (1200-1045 BCE).
 The law in the Han Dynasty (206 BCE – 220 CE) required officials of the empire to rest every 5 days, called "mu", while it was changed into 10 days in the Tang Dynasty (618 CE – 907CE), called "huan" or xún (旬). Months were almost 3 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.
===Egypt===
Ancient Egypt had a 10-day week, 3 weeks per month with 5 extra days at the end of the year.
===France===
A 10-day week was used in France for 12 years from late 1793 to 1805; furthermore, the Paris Commune adopted the Revolutionary Calendar for 18 days in 1871.
==Thirteen-day==
===Aztecs===
The Aztecs divided a ritual cycle of 260 days, known as Tonalpohualli, into 20 weeks of 13 days known as Trecena.
===Maya===
The Maya divided a 260 ritual cycle known Tzolk'in as into 20 weeks of 13 days known as Trecena.
==Twenty-day==
===Aztecs===
The Aztecs divided a solar year of 365 days, Xiuhpohualli into 18 periods of 20 days and 5 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.
===Maya===
The Maya also divided the year, Haab', into 18 periods of 20 days, Uinal, and 5 nameless days known as Wayeb'.
==Other==
===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.
===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 6, 7, 8, or 9 days depending on the actual time difference between the full moon, First Quarter, new moon and Last Quarter.
==References==
==Further reading==
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Category:Days of the week