Seven-day week

For more information on other weeks, see Week. For more information each day of the week, see Week-day names.

See also: Planetary hours

The seven-day week is used by the majority of the world and is the international standard as specified in ISO 8601.

Origins

The origin of the seven-day week is the religious significance that was placed on the seventh day by ancient cultures, including the Babylonian civilization and the Jewish religion. Jews celebrated every seventh day, within a continuous cycle of seven-day weeks, as a holy day of rest from their work; although it is possible that the Hebrew origin of the seven-day week was lunar, and not perpetual. Similarly, the Babylonians also celebrated the seventh day of each seven-day week as a holy day, but adjusted the number of days of the final week in their month so that their monthly calendar would always commence on the new moon. This may further be reflected in the contemporary and traditional Zoroastrian calendars that relates to the first, seventh and so on days of the month as pertaining to Ahura Mazda (God). Historically, a number of other major religio-cultural groups, such as Christians and Muslims, have continued to regularly hold religious events on a specific day within each seven-day week.

The seven-day week is approximately a quarter of a lunation, so it has been proposed that this is the implicit, astronomical origin of the seven-day week. However, there are a number of problems with this proposal. The seven-day week is actually only 23.7% of a lunation, which means that a continuous cycle of seven-day weeks rapidly loses synchronisation with the lunation. This problem is compounded by the fact that a lunation is only the mean time for the lunar phase cycle, with each individual lunar phase varying in length. Also, the duodecimal (base-12) and sexagesimal (base-60) numeral systems have historically been the primary systems used to divide other chronological and calendar units. Therefore, it is not immediately apparent why the seven-day week was selected by ancient cultures, rather than a week that included a number of days that was a factor of these numeral systems, such as a six-day or a twelve-day week, or a week that divided the lunation more accurately using a factor of these number systems, such as a five-day or ten-day week. Finally, there are no historical Jewish or Babylonian records that confirm that these cultures explicitly defined the seven-day week as a quarter of a lunation.

A more obvious pattern, shrouded in the taboos of monotheistic religions, is that the seven-day week arises from the fact that there are seven objects in the solar system visible to the naked eye from Earth – the Sun, the Moon and the five classical naked eye planets: Mars, Mercury, Jupiter, Venus, and Saturn. In early religions, these may have represented the most important Gods, with Monday and Friday usually being linked to the two main matriarchal Goddesses of Motherhood and Love, with the rest being left over for the patriarchal Gods. The pattern can be most clearly seen in the French language which gives us Lundi, from "dies Lunae", the day of the Moon; Mardi, from "dies Martis", the day of Mars; Mercredi, from "dies Mercurii", the day of Mercury; Jeudi, from "dies Jovis", the day of Jupiter; Vendredi, from "dies Veneris", the day of Venus; and Samedi, from "dies Saturni", the day of Saturn. According to this pattern, the final day of the week in French should be Soldi, from "dies Solis", though it is of course Dimanche, from "dies Dominica", which is the day of the Lord. Getting back to the English language, the words "Day" and "Deity" may also be related via this ancient primitive religious origin, through the Proto-Indo-European word "dyeu", meaning "to shine". In English, you can also see this planetary pattern, if you work through the day-naming scheme of Julius Caesar, in which Germanic Gods and Goddesses were substituted for Roman ones, with Tiu for belligerent Mars, Woden for quicksilver Mercury, Thor for thunderbolt Jupiter, and Freya for voluptuous Venus. Sunday and Monday are fairly obvious inserts for the Sun and the Moon, and because Caesar could identify no Germanic God who was the father of Woden, this leaves us with Saturday named directly after the Roman God Saturn (Greek Cronos), who was the father of Jupiter (Greek Zeus). Let us be thankful that Caesar neglected to uncover Ymir, the father of Woden, otherwise Saturday night entertainment would be Ymirday night entertainment, or more likely through the passage to time, Yumday night entertainment. We must also remember the ancient Greeks too, who used their own God and Goddess names for days of the week, which the Romans later copied and translated into their own equivalent deities. The ancient Greek days were hemera helio, "day of the sun"; hemera selenes, "day of the moon"; hemera Areos, "day of Ares"; hemera Hermu, "day of Hermes"; hemera Dios, "day of Zeus"; hemera Aphrodites, "day of Aphrodite"; and hemera Khronu, "day of Cronus". No doubt many other ancient early religions and cultures who adopted a seven-day week also used the same pattern to name their own days of the week, especially the Proto-Indo-Europeans.

Ancient Near East

The Babylonian Imago Mundi, dated to the 6th century BC (Neo-Babylonian Empire). The map shows Babylon on the Euphrates, surrounded by a circular landmass showing Assyria, Armenia and several cities, in turn surrounded by a "bitter river" (Oceanus), with seven islands arranged around it so as to form a seven-pointed star.

Further information: Babylonian calendar

Counting from the new moon, the Babylonians celebrated the 7th, 14th, 21st, and 28th as "holy-days", also called "evil days" (meaning "unsuitable" for prohibited activities). On these days officials were prohibited from various activities and common men were forbidden to "make a wish", and at least the 28th was known as a "rest-day". On each of them, offerings were made to a different god and goddess. Tablets from the sixth-century B.C. reigns of Cyrus the Great and Cambyses indicate these dates were sometimes approximate. The lunation of 29 or 30 days basically contained three seven-day weeks, and a final week of eight or nine days inclusive, breaking the continuous seven-day cycle. The Babylonians additionally celebrated the 19th as a special "evil day", the "day of anger", because it was roughly the 49th day of the (preceding) month, completing a "week of weeks", also with sacrifices and prohibitions. Further, reconstruction of a broken tablet seems to define the rarely attested Sapattu^m or Sabattu^m as the 15th day of the lunation: this word is cognate with Hebrew Shabbat, but is monthly rather than weekly; it is regarded as a form of Sumerian sa-bat ("mid-rest"), attested in Akkadian as um nuh libbi ("day of mid-repose").

A seven-day week is mentioned in the Creation story contained in the Book of Genesis, in the Hebrew Bible, where God is said to have created the heavens and the earth in six days and rested on the seventh (Genesis 1:1–2:3). Also, in the Book of Exodus, the fourth of the ten commandments is to rest on the seventh day, the Sabbath, which can be seen as implicating a seven-day week social institution (Exodus 20:8–11).

Classical Antiquity

Frank C. Senn in his book Christian Liturgy: Catholic and Evangelical points to data suggesting evidence of an early continuous use of a seven-day week; referring to the Jews during the Babylonian Captivity in the 6th century BCE, after the destruction of the Temple of Solomon.

The ancient Romans traditionally used the eight-day nundinal cycle, but after the adoption of the Julian calendar, in the time of Augustus, the seven-day week came into use. For a while, the week and the nundinal cycle coexisted, but by the time the week was officially adopted by Constantine in AD 321 the nundinal cycle had fallen out of use.

The association of the days of the week with the Sun, the Moon, and the five planets visible to the naked eye dates to the Roman era (2nd century).

Christian Europe

The seven-day weekly cycle is reputed to have remained unbroken in Europe for almost two millennia, despite changes to the Alexandrian, Julian, and Gregorian calendars.

The date of Easter Sunday can be traced back through numerous computistic tables to an Ethiopic copy of an early Alexandrian table beginning with the Easter of 311 AD.

Adoption after other systems

China

The earliest known reference in Chinese writings to a seven-day week is attributed to Fan Ning, who lived in the late 4th century in the Jin Dynasty, while diffusions from the Manichaeans are documented with the writings of the Chinese Buddhist monk Yi Jing and the Ceylonese or Central Asian Buddhist monk Bu Kong of the 7th century (Tang Dynasty).

France

Main article: French republican calendar

France discontinued the seven-day week for a ten-day week with the introduction of the republican calendar in 1793. The Concordat of 1801, which re-established the Roman Catholic Church in France, also restored the seven-day week, beginning with Easter Sunday, 18 April 1802.

Japan

The Chinese transliteration of the planetary system was soon brought to Japan by the Japanese monk Kobo Daishi. Surviving diaries of the Japanese statesman Fujiwara Michinaga show the seven-day system in use in Heian Japan as early as 1007. In Japan, the seven-day system was kept in use for astrological purposes until its promotion to a full-fledged Western-style calendrical basis during the Meiji era.

Hindu

The seven-day week may have been in use during the Vedic Period, although according to Pandurang Vaman Kane author of History of Dharmasastra "this is not conclusive".

The Pañcasiddhāntikā mentions 'Monday'. The Garga dated 1st Century BCE, refers to the seven-day week, Sunday to Saturday.

He concludes "the above references furnish a terminus ad quem (viz. 1st century BCE–1st century CE) The terminus a quo cannot be stated with certainty".

Soviet Union

Main article: Soviet calendar

In 1929 USSR discontinued the seven-day week for a five-day week, then a six-day week. While the days were still named according to the seven-day week, the work schedules were rotated in five- and six-day periods. The seven-day week was reintroduced on 27 June 1940.

Week numbering

Weeks in a Gregorian calendar year can be numbered for each year. This style of numbering is commonly used (for example, by schools and businesses) in some European and Asian countries, but rare elsewhere.

ISO 8601 includes the ISO week date system, a numbering system for weeks – each week begins on a Monday and is associated with the year that contains that week's Thursday (so that if a year starts in a long weekend Friday–Sunday, week number one of the year will start after that). For example, week 1 of 2004 (2004W01) ran from Monday 29 December 2003 to Sunday, 4 January 2004, because its Thursday was 1 January 2004, whereas week 1 of 2005 (2005W01) ran from Monday 3 January 2005 to Sunday 9 January 2005, because its Thursday was 6 January 2005 and so the first Thursday of 2005. The highest week number in a year is either 52 or 53 (it was 53 for year 2004). Schematically, this ISO convention translates as follows:

Dates in January							Effect
M	T	W	T	F	S	S	Week number	Week assigned to
1	2	3	4	5	6	7	1	New year
	1	2	3	4	5	6	1	New year
		1	2	3	4	5	1	New year
			1	2	3	4	1	New year
				1	2	3	52 or 53	Previous year
					1	2	52 or 53	Previous year
						1	52 or 53	Previous year

In some countries, though, the numbering system is different from the ISO standard. At least six numberings are in use:

First day of week	First week of year contains			Weeks assigned twice	Used by/in
Monday	4 January	1st Thursday	4–7 days of year	no	Most of Europe and countries adhering to ISO 8601
Saturday	1 January	1st Friday	1–7 days of year	yes	Much of the Middle East
Sunday	1 January	1st Saturday	1–7 days of year	yes	Canada, USA

Facts and figures

• 1 week = 7 days = 168 hours = 10,080 minutes = 604,800 seconds (except at daylight saving time transitions or leap seconds)
• 1 Gregorian calendar year = 52 weeks + 1 day (2 days in a leap year)
• 1 week = 1600⁄6957 ≈ 22.9984% of an average Gregorian month

In a Gregorian mean year there are 365.2425 days, and thus exactly 52+71⁄400 or 52.1775 weeks (unlike the Julian year of 365.25 days or 52+5⁄28 ≈ 52.1786 weeks, which cannot be represented by a finite decimal expansion). There are exactly 20871 weeks in 400 Gregorian years, so 30 April 1611 was a Saturday just like 30 April 2011.

A system of Dominical letters has been used to determine the day of week in the Gregorian or the Julian calendar.

See also

• Calculating the day of the week
• Dominical letter
• Workweek
• Hebrew calendar
• Broadcast calendar
• Lunar phase

External links

• Week Wheel for Children