A week (in the Western and international context) is a unit of time equal to seven days. It is the standard calendrical period between a day and a month in most parts of the world. There are just over 52 weeks in a year, or on average weeks in a month. The days of the week are often used to set work days, rest days, and holy days. The term "week" is also used to refer to a sub-section of the week, such as the workweek and weekend. Certain weeks within a year may be designated for a particular purpose, such as Golden Week in China and Japan. More informally, certain groups may advocate awareness weeks, such as National Family Week in Canada, which are designed to draw attention to a certain subject or cause.
Some ancient and traditional cultures have or had different week lengths, including ten days in Egypt, an eight-day week for Etruscans and ancient Romans, and four- or five-day weeks between market days in modern West Africa. (See also the Japanese ten-day jun, used alongside the 7-day week.) The Romans later switched to a seven-day week.Zerubavel (1989: 14–15)Bultrighini & Stern (2021: 22–38) This was originally a so-called planetary or astrological week, a cycle of disputed originsCf. (Bultrighini & Stern 2021: 22–27) vs Zerubavel (1989: 12–19) that named each day after a classical planet and the god identified with that planet. Due to the spread of Christianity, the Romans' astrological week was identified and merged with the Christian seven-day week centred on Sunday (the day of the Resurrection of Christ), which had originated with the Jewish seven-day week centred on Saturday.Zerubavel (1989: 23–24)Bultrighini & Stern (2021: 47) Both the astrological week and the Jewish week may have been inspired by seven-day cycles in the Babylonian calendar,Why Are There Seven Days in a Week?. Discover (15 January 2020). Retrieved 2022-10-22. although the evidence for that is weak.Baker, Nick and Joey Watson. Where does the seven-day week come from and why does it govern our lives? ABC Radio National. 4 Jan 2022 In AD 321, Emperor Constantine the Great decreed a seven-day week in the Roman Empire, including making Sunday a public holiday. This spread across Europe, then the rest of the world.
In English, the days use Germanic equivalents of the Roman names, apart from Saturday, which had no equivalent: Sunday (Sol/sun day), Monday (Luna/moon day), Tuesday (Mars/Tiw's day), Wednesday (Mercury/Woden's day), Thursday (Jupiter/Thor's day), Friday (Venus/Friga's day), and Saturday (Saturn day).
Which days of the week are designated the first and the last varies by culture, though virtually all have Saturday, Sunday, or Monday as the first day.
The three Abrahamic religions observe different days of the week as their holy day.World Book Encyclopedia, 2018 ed., s.v. "Jerusalem" Christians observe the Sabbath on Sunday (see Sabbath in Christianity), traditionally the first day of the week, in honor of the resurrection of Jesus. Muslims observe the Sabbath on Friday (see Friday prayer), because it was described as a sacred day of congregational worship in the Quran. Jews observe the Sabbath on Saturday (Shabbat), the seventh day, in honor of God's creation of the world in six days and resting on the seventh.
Name The English word week comes from the Old English , ultimately from a Common Germanic , from a root "turn, move, change". The Germanic word probably had a wider meaning before the Roman calendar was adopted, perhaps "succession series", as suggested by Gothic translating "order" in Luke 1:8.
The seven-day week is named in many languages by a word derived from "seven". The archaism sennight ("seven-night") preserves the old Germanic practice of reckoning time by nights, as in the more common fortnight ("fourteen-night").sennight at worldwidewords.org (retrieved 12 January 2017) Hebdomad and hebdomadal week both derive from the Greek (, "a seven"). Septimana is cognate with the Romance terms derived from Latin ("seven mornings").
Definition and duration A week is defined as an interval of exactly seven days, so that, except when passing through daylight saving time transitions or leap seconds, 1 week = 7 days = 168 hours = 10,080 minutes = 604,800 seconds. With respect to the Gregorian calendar: 1 Gregorian calendar year = 52 weeks + 1 day (2 days in a leap year) 1 week = ≈ 22.9984% of an average Gregorian month
In a Gregorian mean year, there are 365.2425 days, and thus exactly or 52.1775 weeks (unlike the Julian year of 365.25 days or ≈ 52.1786 weeks). There are exactly 20,871 weeks in 400 Gregorian years, so was a , just as was .
Relative to the path of the Moon, a week is 23.659% of an average lunation or 94.637% of an average quarter lunation.
Historically, the system of dominical letters (letters A to G identifying the weekday of the first day of a given year) has been used to facilitate calculation of the day of week. The day of the week can be easily calculated given a date's Julian day number (JD, i.e. the integer value at noon UT): Adding one to the remainder after dividing the Julian day number by seven (JD modulo 7 + 1) yields that date's ISO 8601 day of the week. For example, the Julian day number of is . Calculating yields , corresponding to .Richards, E. G. (2013). "Calendars". In S. E. Urban & P. K. Seidelmann, eds. Explanatory Supplement to the Astronomical Almanac, 3rd ed. (pp. 585–624). Mill Valley, Calif.: University Science Books. 2013, pp. 592, 618. This is equivalent to saying that JD0, i.e. 1 January 4713 BCE of the proleptic Julian calendar, was a Monday. In 1973, John Conway devised the Doomsday rule for mental calculation of the weekday of any date in any year.
Start and end
Cultures vary as to which days of the week are designated the first and the last on their calendars, though virtually all have Saturday, Sunday, or Monday as the first day. The International Organization for Standardization uses Monday as the first day of the week in its ISO week date system through the international ISO 8601 standard. Most of Europe, China, West and Central Africa, and Oceania count Monday as the first day of the week, while much of America, South and Southeast Asia, and southern Africa count Sunday as the first. Most Arabic- and Persian-speaking countries use Saturday as the first day of the week, though some use Monday (Lebanon, Morocco, Tunisia and Tajikistan) or Sunday (Saudi Arabia and Yemen). Other regions are mixed, but nearly all observe either Sunday or Monday as the first day. The first day used in calendars may differ from the numbered "name" of the day in a particular place.
Days of the week
The days of the week were named for the seven classical planets, which included the Sun and Moon. This naming system persisted alongside an "ecclesiastical" tradition of numbering the days in ecclesiastical Latin beginning with Dominica (the Lord's Day) as the first day. The Greco-Roman gods associated with the classical planets were rendered in their interpretatio germanica at some point during the late Roman Empire, yielding the Germanic tradition of names based on indigenous deities.
The ordering of the weekday names is not the classical order of the planets (by distance in the planetary spheres model, which is Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn); nor, equivalently, by their apparent speed of movement in the night sky. Instead, the planetary hours systems resulted in succeeding days being named for planets that are three places apart in their traditional listing. Plutarch apparently discussed this in a treatise written AD 100, which is reported to have addressed the question Why are the days named after the planets reckoned in a different order from the actual order? (the text of the treatise has been lost).E. G. Richards, Mapping Time, the Calendar and History, Oxford 1999. p. 269. Dio Cassius (early 3rd century) gives two explanations in a section of his Historia Romana after mentioning the Jewish practice of sanctifying the day called the day of Kronos (Saturday). Book 37, Sections 16–19. English translation.
Sunday Monday Tuesday Wednesday Thursday Friday SaturdayPlanet Sun Moon Mars Mercury Jupiter Venus Saturn Greco-Roman deity Helios-Sol Selene-Luna Ares-Mars Hermes-Mercury Zeus-Jupiter Aphrodite-Venus Cronus-Saturn Greek: Latin: Sun Moon Tiwaz Wodanaz Þunraz Frige — Old English
An ecclesiastical, non-astrological, system of numbering the days of the week was adopted in Late Antiquity. This model also seems to have influenced (presumably via Gothic) the designation of Wednesday as "mid-week" in Old High German () and Old Church Slavonic (, srěda, literally, middle day). Old Church Slavonic may have also modeled the name of Monday, (literally, the day after Sunday), after the Latin .Max Vasmer, , s.v. . However, the Slavic languages later introduced a secondary numbering system that names Tuesday as the "second day".
The ecclesiastical system became prevalent in Eastern Christianity, but in the Latin West it remains extant only in modern Icelandic, Galician, and Portuguese.the latter specifically due to the influence of Martin of Braga, 6th-century archbishop of Braga.
"First Day" or "Lord's Day" (Sunday) "Second Day" (Monday) "Third Day" (Tuesday) "Fourth Day" (Wednesday) "Fifth Day" (Thursday) "Sixth Day" or "Jumu'ah"(Friday) "Seventh Day" or "Sabbath" (Saturday) Greek /kiriaki iméra/ /devtéra iméra/ /tríti iméra/ /tetárti iméra/ /pémpti iméra/ /paraskevi iméra/"day of preparation", i.e. the day before Sabbath, cf. Luke 23:54 () /sáb:aton/ Latin ;rarely ;rarely ; rarely Hebrew
History
Ancient Near East The earliest evidence of an astrological significance of a seven-day period is a decree of king Sargon of Akkad around 2300 BC. Akkadians venerated the number seven, and the key celestial bodies visible to the naked eye numbered seven (the Sun, the Moon and the five closest planets).
Gudea, the priest-king of Lagash in Sumer during the Gutian dynasty (about 2100 BC), built a seven-room temple, which he dedicated with a seven-day festival. In the flood story of the Assyro-Babylonian Epic of Gilgamesh, the storm lasts seven days, the dove is sent out after seven days (as in Genesis), and the Noah-like character of Utnapishtim leaves the ark seven days after it reaches firm ground.
Counting from the new moon, the Babylonians celebrated the 7th, 14th, 21st and 28th of the approximately 29- or 30-day lunar month as "holy days", also called "evil days" (meaning inauspicious for certain activities). On those days, officials were prohibited from various activities and common men were forbidden to "make a wish", and at least the 28th was a "rest day". On each of them, offerings were made to a different god and goddess. Though similar, the later practice of associating days of the week with deities or planets is not due to the Babylonians.
Tablets from the Achaemenid period indicate that 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 also 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.
Achaemenid Persia The Zoroastrian calendar follows the Babylonian in relating the 7th, 14th, 21st, and 28th of the 29- or 30-day lunar month to Ahura Mazda.Boyce, Mary (ed. & trans.). Textual Sources for the Study of Zoroastrianism. University of Chicago Press, 1984, pp. 19–20. The forerunner of all modern Zoroastrian calendars is the system used to determine dates in the Persian Empire, adopted from the Babylonian calendar by the 4th century BC.
Judaism A continuous seven-day cycle that runs throughout history without reference to the phases of the moon was first practiced in Judaism, dated to the 6th century BC at the latest.