week, period of time shorter than the month, commonly seven days. The ancient Egyptians used a 10-day period, as did the French under the short-lived French Revolutionary calendar. In many regions a four-day to eight-day market week is based on the recurrence of market days; the early Romans observed an eight-day market week. This period also corresponds roughly with the moon's quarter phases, which come every seven or eight days. The seven-day week is said to have originated in ancient times in W Asia, probably in Mesopotamia. This is thought to have been a planetary week predicated on the astrological concept of the influence of the planets, which were long erroneously believed to be seven celestial bodies revolving around the earth; these were the sun and moon and five of the bodies recognized today as planets—Mars, Mercury, Jupiter, Venus, and Saturn. The Hebrew week is based chiefly on the religious observance of the Sabbath, which comes every seventh day and is usually associated with the seventh day of creation, when the Lord rested from his labors. The Christian week and the Muslim week were probably derived chiefly from the Hebrew week, although the weekly holy days are different (Hebrew, Sabbath, seventh day; Christian, Sunday, first day; Muslim, Friday, sixth day). The influence of the weeks of Chaldaeans, Christians, and Jews slowly made itself felt in the Roman Empire, and elements of the systems were probably merged. The planetary week was at first preeminent, and the use of planetary names, based on names of pagan deities, continued even after Constantine (c.321) made the Christian week, beginning on Sunday, official in the civil calendar. The Roman names for the days of the week pervaded Western Europe; in most languages the forms are translations from Latin or attempts to assign corresponding names of divinities. The Latin names, their translations, the English equivalents, and their derivations follow: dies solis [sun's day], Sunday; dies lunae [moon's day], Monday [moonday]; dies Martis [Mars' day], Tuesday [Tiw's day]; dies Mercurii [Mercury's day], Wednesday [Woden's day]; dies Jovis [Jove's or Jupiter's day], Thursday [Thor's day]; dies Veneris [Venus' day], Friday [Frigg's day]; and dies Saturni [Saturn's day], Saturday.
A week (also called sennight or sevennight) is a unit of time longer than a day and shorter than a month. In most modern societies the week is a period of seven days. The weekly cycle of seven days runs independently of the cycle of a calendar. The common denominator in both cases is the day.


Europe and Near East

The origin of the concept of the week may be attributed to Genesis 1 and 2 in the Bible, which contains the creation account of the earth, animals, and man in six days, with the sabbath of rest on the seventh day (Genesis 2:2-4). Its existence in ancient cultures may be traced to a divine or spiritual origin for this institution, since there is no celestial explanation to account for it, such as exists with the day, the month, and the year.

Various sources point to the seven day week as having originated in ancient Babylonia or Sumer. It has been suggested that a seven day week might be much older. The seven day planetary week originated in Hellenistic Egypt.

The 1943 Universal Jewish Encyclopedia volume 10 page 482, edited by Isaac Landman under the article “Week”, written by Simon Cohen, Director of Research, summarizes:

Meanwhile, the Roman Republic and then Empire, like the Etruscans, used a "market week" of eight days (known as the nundinal cycle). From around the 1st century CE, with the spread of Christianity, the Roman eight day week was replaced gradually by the seven day week.

The seven day weekly cycle is known 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 CE as described by Otto Neugebauer in Ethiopic astronomy and computus. Only one Roman date with an associated day of the week exists from the first century and it agrees with the modern sequence, if properly interpreted. Jewish dates with a day of the week do not survive from this early period. In the case of the Jewish week, it had been in use for at least 1,000 years before its adoption by the Roman Empire.

The Jewish and Christian seven-day week is modeled on the biblical creation story, in which God created the universe in six days, then rested on the seventh.

Other theories speculate that the fixed seven-day period appeared due to evenly dividing a lunar month into quarters.

The seven-day week became established in both the West and East according to different paths:

Hindu seven-day week

Hindu civilization used a seven-day week. It is mentioned in the Ramayana, a sacred epic written in Sanskrit about 500 BCE, and translated as follows:

Hindu English
Bhanu-vaar Sunday
Soma-vaar Moon-day
Mangal-Vaar   Tuesday
Bud-Vaar Wednesday
Guru-Vaar Thursday
Shukr-Vaar Friday
Shani-Vaar Saturday

The meaning of the name of the days of the week in Sanskrit, above, is equivalent to English names: e.g., "Shani-Vaar," where Shani = Saturn and Vaar = Day.

Chinese seven-day week

The earliest known reference in Chinese writings is attributed to Fan Ning, who lived in the late 4th century, while diffusions via India 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. 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 Period 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.

The Chinese use of the seven day week (and thus Korean, Japanese, Tibetan, and Vietnamese use) traces back to the 600s CE. The 28 stars were arranged in order of sun, moon, fire, water, wood, gold, earth, and every 7 days were called "qi-yao". The days were assigned to each of the luminaries, but the week did not affect social life or the official calendar. The law in the Han Dynasty required officials of the empire to rest every 5 days, called "mu", while it was changed into 10 days in the Tang Dynasty, called "huan" or xún (旬). With months being almost 3 weeks long (alternating 29 and 30 days) 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. The 7 days "week" in ancient China is mostly kept in astrological purposes and cited in several Buddhist texts until the Jesuits reintroduced the concept in the 16th century. Thus the 19th century Japanese, when adopting the seven day western week, took their own astrological week with names for the days of the week that corresponded to the English names (and in fact were better preservations of the original Babylonian concepts, the English day names having been conflated with gods from Germanic mythology).

The week as indicator of market day

Although seven day weeks are common to all modern societies now, anthropologists note that weeks of other durations (varying from three to eight days) are found in many pre-modern societies. They also observe that the name for "week" is often the same as that for "market day", suggesting the concept of a week is likely to arise in any agrarian or pre-agrarian society where people have marketplaces or market days. In sparsely populated areas where trade is not conducted every day it is essential that farmers and consumers agree in advance on what day they will meet, especially if the walk to market takes several hours or days. The week (meaning a fixed count of days) was much simpler and more precise way of doing this when compared with a lunar calendar-based system or a system based on the seasonal rotation of the celestial sphere. Being based on a count kept by people rather than on the relative motion of the moon and stars, the week was not "heavenly", but in the traditional seven-day week, this was overcome by assigning the sun, moon, and the five planets known to the ancients (Jupiter, Mercury, Mars, Venus, Saturn) each to a specific day of the week.

Weeks and the calendar year

The weekly cycle runs concurrently with regular calendar cycles. The weekly cycle is not based on any astronomical phenomena. Besides being of religious significance, it also is convenient in commercial and social contexts. Some novel calendars have been designed which synchronise the weeks and years by adding a leap week or weekless days to the calendar. The advantage of these calendar systems is that each year a given date always falls on the same day of the week. For example, the proposed World Calendar has 52 weeks and one or two extra weekless days each year, which do not count in the weekly cycles. The short-lived 18th century French Revolutionary Calendar had 36 weeks of 10 days and five or six extra weekless days. On the other hand, the former Icelandic calendar had years of 52 or 53 weeks. Instead of adding extra weekless days, the number of weeks in the calendar year varied. An early Norse calendar, from the beginning of the Viking Age, had five day weeks, called fimmts, arranged in 12 months of six fimmts each, with five ceremonial days not part of any month. The Hermetic Lunar Week Calendar uses the lunar week which is a quarter of a lunation and has 6, 7, 8 or 9 days (average 7.382647 days).

First day of the week

In Jewish and Christian tradition, the first day of the week is Sunday. Both the Hebrew and Ecclesiastical Latin languages number most of the days of the week. In Hebrew, Sunday through Friday are numbered one through six, while in Ecclesiastical Latin, Monday through Friday are numbered the second through the sixth days of the week (feria). For Christians and Jews, Sunday remains the first day of the week. Most, though not all, business and social calendars in North America mark Sunday as the first day of the week.

In most of Europe, and some other countries, Monday is considered to be the first day of the week and is literally named as such in languages such as Mandarin (pinyin Xīngqí Yī, literally means Weekday One) and Lithuanian (pirmadienis - means First Day).

The ISO prescribes Monday as the first day of the week with ISO 8601 for software date formats.

Work week and weekends

The seven-day workweek is generally composed of five working days ("weekdays") and two non-working days (the "weekend"), though which days of the week are which varies from country to country. Which day of the week is the "first" day also varies, even among countries that share the same weekend days.

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 = 23.01% of an average month

In a Gregorian mean year there are exactly 365.2425 days, and thus exactly 52.1775 weeks (unlike the Julian year of 365.25 days, which does not contain a number of weeks represented by a finite decimal expansion). There are exactly 20871 weeks in 400 Gregorian years, so 10 April 1605 was a Sunday just like 10 April 2005.

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

Week number

Weeks in a Gregorian calendar year can be numbered for each year. This style of numbering is commonly used (for example, by 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 may be 52 or 53 (it was 53 for year 2004).

The numbering system in different countries may deviate from the international ISO standard. There are at least six possibilities:

First day of week First week of year contains Weeks assigned twice Used by/in
Monday 1 January, 1st Sunday, 1–7 days of year yes UK
Monday 4 January, 1st Thursday, 4–7 days of year no Most of Europe ISO 8601(1988), European Norm EN 28601 (1992)
Monday 7 January, 1st Monday, 7 days of year no
Wednesday 1 January, 1st Tuesday, 1–7 days of year yes
Saturday 1 January, 1st Friday, 1–7 days of year yes
Monday 1 January, 1st Saturday, 1–7 days of year yes USA

Liturgical week

In Christian liturgy, the week is mainly dominated by the special status of the Sunday. The week was regarded as a sacred institution among the Jews owing to the law of the Sabbath rest and its association with the first chapter of Genesis. The earliest Christian converts seem tenacious of the usages (so far as they were compatible with the law of the Gospel) in which they had been brought up. The Sunday, "the first day of the week" (Acts 20:7; 1 Corinthians 16:2; cf. Revelation 1:10), soon replaced the Sabbath as the great day of religious observance, but the week itself remained as before. Indeed, there is much to recommend the idea that in the first and second centuries the only commemorations of the great Christian mysteries formed a weekly, not an annual, cycle. Sunday, according to the Epistle of Barnabas (xv), was "the beginning of another world", and the writer further says: "Wherefore also we keep the eighth day for rejoicing, in the which also Jesus rose from the dead and having been manifested ascended into the heavens". Again the Didache (viii) ordains: "Let not your fasts be with the hypocrites; for they fast on the second [Monday] and fifth [Thursday] days of the week, but do ye fast on the fourth [Wednesday] and on the day of preparation [Friday]", while in c. xiv we are told "And on the Day of the Lord come together and break bread and give thanks". Altogether it becomes clear from the language of Tertullian, the Apostolic Constitution and other early writers that the Sunday in each week was regarded as commemorating the Resurrection, and the Wednesday and Friday the betrayal and Passion of Christ.

Although this simple primitive conception gave place in time, as feasts were introduced and multiplied, to an annual calendar, the week always retained its importance; this is particularly seen in the Divine Office in the hebdomadal division of the Psalter for recitation. Amalarius preserves for us the particulars of the arrangement accepted in the chapel royal at Aachen in 802 CE by which the whole Psalter was recited in the course of each week. In its broader features the division was identical with that theoretically imposed by the Roman Breviary until the recent publication of the Apostolic Constitution "Divine afflatu" on 1 Nov., 1911 CE. Moreover, it appears from Amalarius that the Carlovingian arrangement was in substance the same as that already accepted by the Roman Church. Already in the sixth century, St. Benedict had clearly laid down the principle that the entire Psalter was to be recited at least once in the week; indeed a similar arrangement was attributed to Pope St. Damasus. The consecration of particular days of the week to particular subjects of devotion is also officially recognized by the special Office of the Blessed Virgin on the Saturday, by the Friday Masses of the Passion during Lent and by the arrangement of Votive Offices for special week days approved by Pope Leo XIII. For a long time in the early Middle Ages, Thursday was regarded in the West as a sort of lesser feast or Sunday, probably because it was the day of the week on which the Ascension fell (cf. Bede, Historia ecclesiastica gentis Anglorum, IV, 25). Again the Breviary approved after the Council of Trent left certain devotion accretions to the Office, e.g. the Office for the Dead, Gradual Psalms, etc, to be said once a week, particularly on the Mondays of Advent and Lent.

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