Week
A week is a unit of time equal to seven days. It serves as the standard period for short cycles across most parts of the world. This interval often indicates common work days and rest days alongside days of worship. Weeks map against yearly calendars with just over 52 weeks in a year. The term may also refer to sub-sections like the workweek or weekend. Mathematically, one week equals exactly 168 hours or 10,080 minutes. That duration translates to 604,800 seconds without daylight saving transitions. A Gregorian calendar year contains 52 weeks plus one day. Leap years add an extra day to that count. Relative to the moon, a week represents 23.659% of an average lunation. It covers 94.637% of an average quarter lunation. Historical systems used dominical letters from A to G to identify weekdays. These letters helped calculate the day of the week for any given date. Modern calculations rely on Julian day numbers to determine ISO 8601 weekday values.
King Sargon of Akkad issued a decree around 2300 BCE regarding astrological significance of a seven-day period. Akkadians venerated the number seven while key celestial bodies visible to the naked eye numbered seven. Gudea built a seven-room temple during the Gutian dynasty about 2100 BCE. He dedicated it with a seven-day festival. The Assyro-Babylonian Epic of Gilgamesh describes a storm lasting seven days. Utnapishtim leaves the ark seven days after reaching firm ground. Babylonians celebrated the 7th, 14th, 21st and 28th of lunar months as holy days. Officials were prohibited from activities on these evil days. Common men could not make wishes on those dates. At least the 28th was known as a rest day. Offerings went to different gods and goddesses on each holy day. Ancient Romans traditionally used an eight-day nundinal system before adopting the seven-day cycle. Emperor Constantine decreed a seven-day week in AD 321 within the Roman Empire. Sunday became a public holiday under that imperial order. This later spread across Europe then the rest of the world. An eight-day week existed in ancient Rome and possibly pre-Christian Celtic calendars. Traces of nine-day weeks appear in Baltic languages and Welsh. The ancient Chinese calendar utilized ten-day weeks alongside Egyptian counterparts.
Judaism practiced a continuous seven-day cycle running throughout history without reference to moon phases by the 6th century BCE at the latest. Jews observe their Sabbath called Shabbat on Saturday from sundown Friday to sundown Saturday. They honor God's creation of the world in six days followed by resting on the seventh. Most Christians observe Sunday as the Lord's Day honoring Jesus resurrection. Muslims observe their day of congregation known as Jumu'ah on Friday because it is sacred for congregational worship in the Quran. Islamic beliefs state Allah created clay on Saturday and mountains on Sunday. Trees appeared Monday while things entailing labour emerged Tuesday. Light formed Wednesday and animals spread Thursday. Adam was created after Asr on Friday between afternoon and night. A continuous seven-day weekly cycle remained unbroken in Christendom for almost two millennia despite calendar changes. Easter Sunday dates trace back through computistic tables to an Ethiopic copy starting with Easter of 311 CE. Justin Martyr wrote that the first day after Sabbath remains the eighth according to all cycle numbers yet stays first. An octave period usually starts and ends on Sunday particularly regarding Christmas Day.
The English word week comes from Old English ultimately from Common Germanic roots meaning turn move or change. The Germanic word likely held wider meaning before Roman calendar adoption perhaps succession series. Gothic translates order in Luke 1:8 using this root. Seven-day weeks named many languages derive from words meaning seven. Sennight preserves old Germanic practice of reckoning time by nights like fortnight means fourteen-night. Hebdomad derives from Greek meaning a seven. Septimana connects to Romance terms from Latin meaning seven mornings. Days of the week were named for classical planets including Sun and Moon. This naming system persisted alongside ecclesiastical traditions numbering days beginning Dominica as first day. Greco-Roman gods associated with planets rendered interpretatio germanica during late Roman Empire yielding Germanic names based on indigenous deities. Saturday kept its Roman name while other six days use Germanic equivalents. Ordering weekday names differs from classical planetary distance listing. Planetary hours systems resulted succeeding days named for planets three places apart traditionally. Plutarch discussed why days named after planets differ from actual order around 100 AD. Dio Cassio gave explanations early third century mentioning Jewish sanctifying day called Kronos. Sunday Monday Tuesday Wednesday Thursday Friday Saturday follow specific deity associations.
Cultures vary which days designated first and last though virtually all have Saturday Sunday or Monday as start. International Organization for Standardization uses Monday as first day via ISO 8601 standard. Most Europe and China consider Monday first while North America South Asia many Catholic Protestant countries consider Sunday first. Many Arabic-speaking countries use Saturday as first day in calendar displays like Algeria Egypt Iraq Jordan Kuwait Oman Qatar Sudan others. Lebanon Morocco Tunisia UAE observe Monday while Saudi Arabia Yemen use Sunday. First day used calendars may differ from numbered name of day particular locale. At least six numberings exist globally including Middle Eastern Western traditional Broadcast Calendar systems. Weeks begin either Saturday Sunday or Monday across these frameworks. Workweek Monday through Friday always shares same week number within calendar week system. Years where January 1 falls Friday Saturday Sunday show different agreements among systems. Epidemiological weeks report healthcare statistics beginning Sunday ending Saturday. First epidemiological week ends first Saturday January provided it falls four or more days into month. Semiconductor package date codes often display YYWW format with year digits followed by week numbers. Tire date codes mandated US DOT show WWYY with two week digits then two year digits. The French Republican Calendar divided 30-day months into thirds using ten-day weeks.
ISO week date system dictates each week begins Monday associated with year containing that week's Thursday. Week one determines if January 1 falls Monday Tuesday Wednesday Thursday making that week Week 1. If January 1 falls Friday Saturday Sunday it becomes part last week previous year. Week one starts first Monday after January 1. Examples include 2015W01 starting Monday the 29th of December 2014 ending Sunday the 4th of January 2015. 2021W01 began Monday the 4th of January 2021 ended Sunday the 10th of January 2021 because January 1 fell Friday. Year 2015 had 52 weeks while leap years may contain 53 weeks depending on start dates. Soviet Union used five and six day work weeks between 1929 and 1940 for factory workers. Collective farm workers continued traditional seven-day week during that period. Peak usage of five-day work week reached 72% industrial workers October 1941. From summer 1931 until June 1940 Gregorian month subdivided into five six-day work weeks. Sixth day uniform rest day applied across schedules. 74.2% industrial workers non-continuous schedules mostly six-day work weeks while 25.8% still continuous schedules mostly five-day work weeks. Traditional names continued including Resurrection for Sunday Sabbath for Saturday despite government atheism. International Fixed Calendar kept seven-day week defining year 13 months 28 days each. Eastman Kodak Company adopted it official calendar decades.
Common questions
What is the definition of a week in terms of days and hours?
A week is a unit of time equal to seven days. Mathematically, one week equals exactly 168 hours or 10,080 minutes.
When did King Sargon of Akkad issue a decree about the seven-day period?
King Sargon of Akkad issued a decree around 2300 BCE regarding astrological significance of a seven-day period. This decree occurred when Akkadians venerated the number seven while key celestial bodies visible to the naked eye numbered seven.
Who decreed that Emperor Constantine established a seven-day week in AD 321?
Emperor Constantine decreed a seven-day week in AD 321 within the Roman Empire. Sunday became a public holiday under that imperial order before it spread across Europe then the rest of the world.
Which organization uses Monday as the first day via ISO 8601 standard?
International Organization for Standardization uses Monday as first day via ISO 8601 standard. Week one determines if January 1 falls Monday Tuesday Wednesday Thursday making that week Week 1.
How many weeks are there in a Gregorian calendar year including leap years?
A Gregorian calendar year contains 52 weeks plus one day. Leap years add an extra day to that count and may contain 53 weeks depending on start dates.