Calendar Wiki

A week is a unit of time longer than a day and shorter than a month. In most modern calendars, including the Gregorian calendar, the week is a period of seven days.

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. [1]

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 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 (Mercury, Venus, Mars, Jupiter, Saturn) each to a specific day of the week.

Origin of the seven-day week[]

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

Hindu, Babylonian, and Jewish seven-day week[]

  • Hindu civilization employed a seven-day week, mentioned in the Ramayana, a sacred epic written in Sanskrit about 500 BC, as Bhanu-vaar meaning Sunday, Soma-vaar meaning Moon-day and so forth.
  • The ancient Babylonians observed a seven-day week, stemming from astronomical observation and association. Days and deities were based on the seven heavenly bodies or "luminaries" visible to the naked eye (the Sun, Moon, and 5 visible planets).
  • Other theories speculate that the fixed seven-day period appeared due to evenly dividing a lunar month into quarters.
  • The Hebrew (and later Christian) seven-day week corresponds to the biblical creation story, in which God created the universe in six days, then rested on the seventh.

Chinese seven-day week[]

The Chinese use of the seven day week (and thus Korean, Japanese, Tibetan, and Vietnamese use) traces back to the 600's AD, when the concept of the seven "luminaries" of Babylonia spread to China. The days were assigned to each of the luminaries, but the week did not affect social life or the official calendar. It 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). By contrast, the Japanese names refer to the Chinese Sun, Moon and the five planets. The only difference is that the planets in the Japanese week have Chinese names based on the five elements rather than pagan deities.[2]

Later use of the week[]

Various groups of citizens of the Roman Empire adopted the week, especially those who had spent time in the eastern parts of the empire, such as Egypt], where the 7-day week was in use. Contemporaneously, Christians, following the biblical instruction, spread the week's use along with their religion.

As the early Christians evolved from being Jewish to being a distinct group, various groups evolved from celebrating both the Jewish Sabbath (Saturday) and the first day or the Lord's Day (Sunday), to celebrating only Sunday.

In A.D. 321. the Roman Emperor Constantine regulated the use of the week due to a problem of the myriad uses of various days for religious observance, and established Sunday as the day for religious observance and rest for all groups, not just those Christians and others who were already observing Sunday.

The Jews of the 4th century retained their tradition of Saturday observance, by then 800 to 1700 years old, and continue to do so. Later, after the establishment of Islam, Friday became that religion's day of observance.

The seven-day week soon became a practice among Christians, Jews, and Muslims. Following European colonization and the subsequent rise of global corporate business, the seven-day week has become universal in keeping time, even in cultures that did not practise it before. Because of the two-day weekend, some modern calendars end the week on Sunday and begin it on Monday. The ISO week date, part of the international standard ISO 8601, also defines Monday as the first day of the week. In practice, this means that calendar formats disagree, and that "next week" said on Sunday means "the week beginning tomorrow".

In that international standard, the "first week of the year" is that week which includes the first Thursday of the year. This way the first week of the year does not start with a long weekend (Friday to Sunday), as the New Year's Day itself is a holiday in many countries.

Weeks and Calendar year[]

Although without a direct astronomical basis (seven days is just under a quarter of a lunar month), it is widely used as a unit of time, especially in the social and commercial context. Weeks can be thought of as forming an independent continuous calendar running in parallel with various other calendars.

However, some novel calendars have been designed in which the weeks and years are forced into synchronization by adding a leap week or weekless days into the calendar. The advantage of these calendars is that a given date always falls on the same day of the week every year. For example the proposed World Calendar has 52 weeks and one or two extra days each year, while the 18th century French Revolutionary Calendar had 36 weeks of 10 days and five or six extra days. Alternatively, instead of adding extra days outside of weeks, it is possible to add entire weeks to the calendar if the years are allowed to vary in length —: the former Icelandic calendar had years of 52 or 53 weeks. 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).

Days of the week[]

In English the days of the week are:

Saturday and Sunday are commonly called the weekend and are days of rest and recreation in most western cultures. The other five days are then known as weekdays, a term which before Saturday got a similar secular work exemption applied to all days except the Sunday; compare Feria. Friday and Saturday are days of rest in some Muslim countries and Israel. The biblical Sabbath lasts from Friday sunset to Saturday sunset.

In some countries such as Iran, the weekend is only one day long (Friday) and the week starts on a Saturday. Other Muslim countries have weekends on Thursday and Friday.

The two-day weekend has become prevalent only during the twentieth centuryTemplate:Fact, leading to some calendars placing Sunday at the end of the week. The five-day working week, and some Christians mistaking Sunday worship for observance of the Sabbath day of rest has lead many people in recent years to consider Monday to be the first day of the week.

Both ISO and European norms prescribe Monday as the first day of the week, but ISO-8601 has not been commonly adopted or implemented throughout the world, although it contains important date formatting standards.

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 = 23.00% 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[]

ISO 8601 includes the ISO week date system, a numbering system for weeks; each week is associated with the year in which Thursday occurs. Thus, for example, week 1 of 2004 (2004W01) ran from Monday 29 December 2003 to Sunday, 4 January 2004. The highest week number in a year may be 52 or 53. This style of numbering is commonly used (for example, by businesses) in some European countries, but rare elsewhere.

The numbering system in different countries may deviate from the international ISO standard. There are at least six possibilities[3] [4]:

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
Wednesday 1 January, 1st Tuesday, 1–7 days of year yes
Saturday 1 January, 1st Friday, 1–7 days of year yes
Sunday 1 January, 1st Saturday, 1–7 days of year yes USA
Monday 4 January, 1st Thursday, 4–7 days of year no ISO 8601, Norway, Sweden
Monday 7 January, 1st Monday, 7 days of year no


External links[]

Sources and references[]

  • Falk, Michael (1999). "Astronomical Names for the Days of the Week", Journal of the Royal Astronomical Society of Canada, Vol. 93, p.122. 1999JRASC..93..122F. [1]