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76-468: A week is a unit of time equal to seven days . It is the standard time period used for short cycles of days in most parts of the world. The days are often used to indicate common work days and rest days, as well as days of worship . Weeks are often mapped against yearly calendars . Ancient cultures had different "week" lengths, including ten in Egypt and an eight-day week for Etruscans . The Etruscan week

152-512: A year may be designated for a particular purpose, such as Golden Week in China and Japan , and National Family Week in Canada. More informally, certain groups may advocate awareness weeks , which are designed to draw attention to a certain subject or cause. The term "week" may also be used to refer to a sub-section of the week, such as the workweek and weekend . Cultures vary in which days of

228-561: A civil day can be either 86,401 or 86,399 SI seconds long on such a day. Other than the two-millisecond variation from tidal deceleration, other factors minutely affect the day's length , which creates an irregularity in the placement of leap seconds. Leap seconds are announced in advance by the International Earth Rotation and Reference Systems Service (IERS) , which measures the Earth's rotation and determines whether

304-409: A distant star (assumed to be fixed). Measuring a day as such is used in astronomy . A sidereal day is about 4 minutes less than a solar day of 24 hours (23 hours 56 minutes and 4.09 seconds), or 0.99726968 of a solar day of 24 hours. There are about 366.2422 stellar days in one mean tropical year (one stellar day more than the number of solar days). Besides a stellar day on Earth , other bodies in

380-486: A formation *tъ(žь)dьnь (Serbian тједан , tjedan , Croatian tjedan , Ukrainian тиждень , tyzhden , Czech týden , Polish tydzień ), from *tъ "this" + *dьnь "day". Chinese has 星期 , as it were " planetary time unit ". An older Chinese form is 禮拜 , meaning "week, religious ceremony." A week is defined as an interval of exactly seven days , so that, except when passing through daylight saving time transitions or leap seconds , With respect to

456-415: A leap second is necessary. Discovered by paleontologist John W. Wells , the day lengths of geological periods have been estimated by measuring sedimentation rings in coral fossils , due to some biological systems being affected by the tide. The length of a day at the Earth's formation is estimated at 6 hours. Arbab I. Arbab plotted day lengths over time and found a curved line. Arbab attributed this to

532-477: A new day starting at either the rising or setting of the Sun on the local horizon (Italian reckoning, for example, being 24 hours from sunset, old style). The exact moment of, and the interval between, two sunrises or sunsets depends on the geographical position ( longitude and latitude, as well as altitude), and the time of year (as indicated by ancient hemispherical sundials ). A more constant day can be defined by

608-519: A second as "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium -133 atom ". This makes the SI-based day last exactly 794,243,384,928,000 of those periods. Various decimal or metric time proposals have been made, but do not redefine the day, and use the day or sidereal day as a base unit. Metric time uses metric prefixes to keep time. It uses

684-727: 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 . While the seven-day week in Judaism is tied to Creation account in the Book of Genesis in the Hebrew Bible (where God creates the heavens and the earth in six days and rests on the seventh; Genesis 1:1-2:3, in the Book of Exodus , the fourth of

760-526: A term for the full moon . The Sumerian term has been reconstructed as rendered Sapattu or Sabattu in Babylonian , possibly present in the lost fifth tablet of the Enûma Eliš , tentatively reconstructed "[Sa]bbath shalt thou then encounter, mid[month]ly". However, Niels-Erik Andreasen , Jeffrey H. Tigay , and others claim that the Biblical Sabbath is mentioned as a day of rest in some of

836-669: A total of 27 leap seconds that have been inserted, so roughly once every other year). The term comes from the Old English term dæġ ( /dæj/ ), with its cognates such as dagur in Icelandic , Tag in German , and dag in Norwegian , Danish , Swedish and Dutch – all stemming from a Proto-Germanic root *dagaz . Several definitions of this universal human concept are used according to context, need, and convenience. Besides

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912-532: 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. Though similar, the later practice of associating days of the week with deities or planets is not due to the Babylonians. 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 BCE at

988-548: 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"). Hebdomad and hebdomadal week both derive from the Greek hebdomás ( ἑβδομάς , "a seven"). Septimana is cognate with the Romance terms derived from Latin septimana ("seven mornings"). Slavic has

1064-420: Is near the time of the lower culmination of the Sun on the central meridian of the time zone. Such a day may be called a calendar day . A day is commonly divided into 24 hours, with each hour being made up of 60 minutes, and each minute composed of 60 seconds. A sidereal day or stellar day is the span of time it takes for the Earth to make one entire rotation with respect to the celestial background or

1140-791: Is no precise parallel to the Israelite Sabbatical week. This leads to the conclusion that the Sabbatical week, which is as unique to Israel as the Sabbath from which it flows, is an independent Israelite creation. The seven-day week seems to have been adopted, at different stages, by the Persian Empire , in Hellenistic astrology , and (via Greek transmission ) in Gupta India and Tang China . The Babylonian system

1216-483: Is organized into calendars as dates , almost always into weeks , months and years . A solar calendar organizes dates based on the Sun's annual cycle, giving consistent start dates for the four seasons from year to year. A lunar calendar organizes dates based on the Moon 's lunar phase . In common usage, a day starts at midnight , written as 00:00 or 12:00 am in 24- or 12-hour clocks , respectively. Because

1292-425: Is practiced, and each year there will be one 23-hour civil day and one 25-hour civil day. Due to slight variations in the rotation of the Earth, there are rare times when a leap second will get inserted at the end of a UTC day, and so while almost all days have a duration of 86,400 seconds, there are these exceptional cases of a day with 86,401 seconds (in the half-century spanning 1972 through 2022, there have been

1368-532: The feria prima or the first day of the week; yet, at the same time, figures as the " eighth day ", and has occasionally been so called in Christian liturgy. Justin Martyr wrote: "the first day after the Sabbath, remaining the first of all the days, is called, however, the eighth, according to the number of all the days of the cycle, and [yet] remains the first." Day A collection of sequential days

1444-597: The Coptic , Julian , and Gregorian calendars, demonstrated by the date of Easter Sunday having been traced back through numerous computistic tables to an Ethiopic copy of an early Alexandrian table beginning with the Easter of 311 CE. A tradition of divinations arranged for the days of the week on which certain feast days occur develops in the Early Medieval period. There are many later variants of this, including

1520-623: The Day of the Sun ( dies Solis ) a legal holiday. 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 . 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 BCE. Frank C. Senn in his book Christian Liturgy: Catholic and Evangelical points to data suggesting evidence of an early continuous use of

1596-596: The Earth's rotation – the Earth's rotational period is slowing. Because of the way the second is defined, the mean length of a solar day is now about 86,400.002 seconds, and is increasing by about 2 milliseconds per century. Since the rotation rate of the Earth is slowing, the length of a SI second fell out of sync with a second derived from the rotational period. This arose the need for leap seconds , which insert extra seconds into Coordinated Universal Time (UTC) . Although typically 86,400 SI seconds in duration,

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1672-527: The Gregorian calendar : 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 20,871 weeks in 400 Gregorian years, so 28 November 1624 was a Thursday just as was 28 November 2024. Relative to

1748-478: The Noah -like character of Utnapishtim leaves the ark seven days after it reaches the 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 these days, officials were prohibited from various activities and common men were forbidden to "make

1824-603: The Pharisee and the Publican ( Luke 18:12 ) describes the Pharisee as fasting "twice in the week" ( Greek : δὶς τοῦ σαββάτου , romanized :  dis tou sabbatou ). In the account of the women finding the tomb empty, they are described as coming there "toward the one of the sabbaths" ( Greek : εἰς μίαν σαββάτων, τῇ μιᾷ τῶν σαββάτων ); translations substitute "week" for "sabbaths". The ancient Romans traditionally used

1900-671: The Ten Commandments is to rest on the seventh day, Shabbat , which can be seen as implying a socially instituted seven-day week), it is not clear whether the Genesis narrative predates the Babylonian captivity of the Jews in the 6th century BCE. At least since the Second Temple period under Persian rule, Judaism relied on the seven-day cycle of recurring Sabbaths . Tablets from the Achaemenid period indicate that

1976-525: The atmosphere refracts sunlight in such a way that some of it reaches the ground even when the Sun is below the horizon by about 34 minutes of arc. So the first light reaches the ground when the centre of the Sun is still below the horizon by about 50 minutes of arc. Thus, daytime is on average around 7 minutes longer than 12 hours. Daytime is further divided into morning , afternoon , and evening . Morning occurs between sunrise and noon . Afternoon occurs between noon and sunset , or between noon and

2052-445: The celestial equator ; the speed is the same as the average speed of the real Sun, but this removes the variation over a year as the Earth moves along its orbit around the Sun (due to both its velocity and its axial tilt). In terms of Earth's rotation, the average day length is about 360.9856°. A day lasts for more than 360° of rotation because of the Earth's revolution around the Sun. With a full year being slightly more than 360 days,

2128-485: 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. Difficulties with Friedrich Delitzsch 's origin theory connecting Hebrew Shabbat with

2204-526: 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 28 November 2024 is 2460643. Calculating 2460643 mod 7 + 1 yields 4, corresponding to Thursday. In 1973, John Conway devised the Doomsday rule for mental calculation of the weekday of any date in any year. The days of the week were named for

2280-412: The (contemporary) Julian calendar, 6 February 60 was, however, a Wednesday . This is explained by the existence of two conventions of naming days of the weeks based on the planetary hours system: 6 February was a "Sunday" based on the sunset naming convention, and a "Wednesday" based on the sunrise naming convention. According to Islamic beliefs, the seven-day a week concept started with the creation of

2356-569: The 1st century CE, along with references to the Jewish Sabbath by Roman authors such as Seneca and Ovid . When the seven-day week came into use in Rome during the early imperial period, it did not immediately replace the older eight-day nundinal system. The nundinal system had probably fallen out of use by the time Emperor Constantine adopted the seven-day week for official use in CE 321, making

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2432-513: The Babylonian lunar cycle include reconciling the differences between an unbroken week and a lunar week, and explaining the absence of texts naming the lunar week as Shabbat in any language. In Jewish sources by the time of the Septuagint , the term "Sabbath" ( Greek : Σάββατον , romanized :  Sábbaton ) by synecdoche also came to refer to an entire seven-day week, the interval between two weekly Sabbaths. Jesus's parable of

2508-522: The Earth's daily orbit around the Sun is slightly less than 1°, so the day is slightly less than 361° of rotation. Elsewhere in the Solar System or other parts of the universe , a day is a full rotation of other large astronomical objects with respect to its star. For civil purposes, a common clock time is typically defined for an entire region based on the local mean solar time at a central meridian. Such time zones began to be adopted about

2584-519: The Eve of Saint Agnes are remnants of the older pattern when holidays began during the prior evening. The common convention among the ancient Romans , ancient Chinese and in modern times is for the civil day to begin at midnight, i.e. 00:00, and to last a full 24 hours until 24:00, i.e. 00:00 of the next day. The International Meridian Conference of 1884 resolved That the Conference expresses

2660-535: The German Bauern-Praktik and the versions of Erra Pater published in 16th to 17th century England, mocked in Samuel Butler 's Hudibras . South and East Slavic versions are known as koliadniki (from koliada , a loan of Latin calendae ), with Bulgarian copies dating from the 13th century, and Serbian versions from the 14th century. Medieval Christian traditions associated with

2736-484: 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, 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. This characteristic

2812-581: The Jewish week was adopted from the Babylonians while removing the moon-dependency. George Aaron Barton speculated that the seven-day creation account of Genesis is connected to the Babylonian creation epic, Enûma Eliš , which is recorded on seven tablets. In a frequently-quoted suggestion going back to the early 20th century, the Hebrew Sabbath is compared to the Sumerian sa-bat "mid-rest",

2888-666: The Solar System have day times, the durations of these being: In the International System of Units (SI), a day not an official unit, but is accepted for use with SI . A day, with symbol d, is defined using SI units as 86,400 seconds; the second is the base unit of time in SI units . In 1967–68, during the 13th CGPM (Resolution 1), the International Bureau of Weights and Measures (BIPM) redefined

2964-451: The Sun passing through the local meridian , which happens at local noon (upper culmination ) or midnight (lower culmination). The exact moment is dependent on the geographical longitude, and to a lesser extent on the time of the year. The length of such a day is nearly constant (24 hours ± 30 seconds). This is the time as indicated by modern sundials. A further improvement defines a fictitious mean Sun that moves with constant speed along

3040-440: The change of water volume present affecting Earth's rotation. For most diurnal animals, the day naturally begins at dawn and ends at sunset. Humans, with their cultural norms and scientific knowledge, have employed several different conceptions of the day's boundaries. In the Hebrew Bible , Genesis 1:5 defines a day in terms of "evening" and "morning" before recounting the creation of the Sun to illuminate it: "And God called

3116-437: The day as the base unit, and smaller units being fractions of a day: a metric hour ( deci ) is 1 ⁄ 10 of a day; a metric minute ( milli ) is 1 ⁄ 1000 of a day; etc. Similarly, in decimal time, the length of a day is static to normal time. A day is also split into 10 hours, and 10 days comprise a décade – the equivalent of a week. 3 décades make a month. Various decimal time proposals which do not redefine

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3192-609: The day called the day of Kronos (Saturday). Ravivāra/Bhānuvāsara/ Ādityavāra Somavāra/ Induvāsara Saumyavāsara Sthiravāsara 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 ( mittawehha ) and Old Church Slavonic ( срѣда ). Old Church Slavonic may have also modeled

3268-445: The day do not have set times; they can vary by lifestyle or hours of daylight in a given place. Daytime is the part of the day during which sunlight directly reaches the ground, assuming that there are no obstacles. The length of daytime averages slightly more than half of the 24-hour day. Two effects make daytime on average longer than night. The Sun is not a point but has an apparent size of about 32 minutes of arc . Additionally,

3344-424: The day of 24 hours (86,400 seconds), the word day is used for several different spans of time based on the rotation of the Earth around its axis. An important one is the solar day , the time it takes for the Sun to return to its culmination point (its highest point in the sky). Due to an orbit's eccentricity, the Sun resides in one of the orbit's foci instead of the middle. Consequently, due to Kepler's second law ,

3420-514: The day: Henri de Sarrauton's proposal kept days, and subdivided hours into 100 minutes; in Mendizábal y Tamborel's proposal, the sidereal day was the basic unit, with subdivisions made upon it; and Rey-Pailhade's proposal divided the day 100 cés. The word refers to various similarly defined ideas, such as: Mainly due to tidal deceleration – the Moon's gravitational pull slowing down

3496-632: The earliest layers of the Pentateuch dated to the 9th century BCE at the latest, centuries before the Babylonian exile of Judah . They also find the resemblance between the Biblical Sabbath and the Babylonian system to be weak. Therefore, they suggest that the seven-day week may reflect an independent Israelite tradition. Tigay writes: It is clear that among neighboring nations that were in position to have an influence over Israel – and in fact which did influence it in various matters – there

3572-405: The eight-day nundinum but, after the Julian calendar had come into effect in 45 BCE, the seven-day week came into increasing use. For a while, the week and the nundinal cycle coexisted, but by the time the week was officially adopted by Constantine in 321 CE, 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

3648-445: The evening twilight begins at sunset and ends at dusk . Both periods of twilight can be divided into civil twilight , nautical twilight , and astronomical twilight . Civil twilight is when the sun is up to 6 degrees below the horizon; nautical when it is up to 12 degrees below, and astronomical when it is up to 18 degrees below. Night is the period in which the sky is dark ; the period between dusk and dawn when no light from

3724-549: The first day of the week. Prior to 2000, Saturday was judged as the first day of the week in much of the Middle East and North Africa due to the Islamic influence; however, this is no longer the case. Other regions are mixed, but typically observe either Sunday or Monday as the first day. The three Abrahamic religions observe different days of the week as their holy day. Jews observe their Sabbath ( Shabbat ) on Saturday,

3800-481: The hope that as soon as may be practicable the astronomical and nautical days will be arranged everywhere to begin at midnight. In ancient Egypt the day was reckoned from sunrise to sunrise. Prior to 1926, Turkey had two time systems: Turkish , counting the hours from sunset, and French , counting the hours from midnight. Humans have divided the day in rough periods, which can have cultural implications, and other effects on humans' biological processes. The parts of

3876-728: The hours of Friday, i. e. between afternoon and night. 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 ). The Chinese variant of

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3952-625: 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 BCE), 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 for seven days, the dove is sent out after seven days (similarly to Genesis), and

4028-419: The latest. There are several hypotheses concerning the origin of the biblical seven-day cycle. Friedrich Delitzsch and others suggested that the seven-day week being approximately a quarter of a lunation is the implicit astronomical origin of the seven-day week, and indeed the Babylonian calendar used intercalary days to synchronize the last week of a month with the new moon. According to this theory,

4104-535: The light Day, and the darkness he called Night. And the evening and the morning were the first day." The Jewish day begins at either sunset or nightfall (when three second- magnitude stars appear). Medieval Europe also followed this tradition, known as Florentine reckoning: In this system, a reference like "two hours into the day" meant two hours after sunset and thus times during the evening need to be shifted back one calendar day in modern reckoning. Days such as Christmas Eve , Halloween (“All Hallows’ Eve”), and

4180-465: The lucky or unlucky nature of certain days of the week survived into the modern period. This concerns primarily Friday , associated with the crucifixion of Jesus . Sunday , sometimes personified as Saint Anastasia , was itself an object of worship in Russia, a practice denounced in a sermon extant in copies going back to the 14th century. Sunday , in the ecclesiastical numbering system also counted as

4256-419: The middle of the 19th century when railroads with regularly occurring schedules came into use, with most major countries having adopted them by 1929. As of 2015, throughout the world, 40 such zones are now in use: the central zone, from which all others are defined as offsets, is known as UTC+00 , which uses Coordinated Universal Time (UTC) . The most common convention starts the civil day at midnight : this

4332-459: The naked eye dates to the Roman era (2nd century). The continuous seven-day cycle of the days of the week can be traced back to the reign of Augustus ; the first identifiable date cited complete with day of the week is 6 February 60 CE, identified as a " Sunday " (as viii idus Februarius dies solis "eighth day before the ides of February, day of the Sun") in a Pompeiian graffito. According to

4408-597: The name of Monday, понєдѣльникъ , after the Latin feria Secunda . The ecclesiastical system became prevalent in Eastern Christianity , but in the Latin West it remains extant only in modern Icelandic , Galician , and Portuguese . The earliest evidence of an astrological significance of a seven-day period is decree of king Sargon of Akkad around 2300 BCE. Akkadians venerated the number seven, and

4484-477: The number 7 as the basis for the Jewish week might have had an Assyrian or Babylonian origin, yet it is crucial to remember that the ancient dwellers of Mesopotamia themselves did not have a seven-day week." The astrological concept of planetary hours is an innovation of Hellenistic astrology, probably first conceived in the 2nd century BCE. The seven-day week was widely known throughout the Roman Empire by

4560-434: 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

4636-553: The planet travels at different speeds at various positions in its orbit, and thus a solar day is not the same length of time throughout the orbital year. Because the Earth moves along an eccentric orbit around the Sun while the Earth spins on an inclined axis, this period can be up to 7.9 seconds more than (or less than) 24 hours. In recent decades, the average length of a solar day on Earth has been about 86,400.002 seconds (24.000 000 6 hours). There are currently about 365.2421875 solar days in one mean tropical year . Ancient custom has

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4712-612: The planetary system was brought to Japan by the Japanese monk Kūkai (9th century). 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 Period (1868–1912). The seven-day week

4788-447: The rest of the world. In English, the names of the days of the week are Sunday , Monday , Tuesday , Wednesday , Thursday , Friday , and Saturday . In many languages, including English, the days of the week are named after gods or classical planets. Saturday has kept its Roman name, while the other six days use Germanic equivalents. Such a week may be called a planetary week (i.e., a classical planetary week). Certain weeks within

4864-423: The same day. In specific applications, the definition of a day is slightly modified, such as in the SI day (exactly 86,400 seconds ) used for computers and standards keeping , local mean time accounting of the Earth's natural fluctuation of a solar day , and stellar day and sidereal day (using the celestial sphere ) used for astronomy . In most countries outside of the tropics , daylight saving time

4940-456: 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

5016-402: The seventh day, from sundown Friday to sundown Saturday, in honor of God's creation of the world in six days and then resting on the seventh. Most Christians observe Sunday (the Lord's Day ), the first day of the week in traditional Christian calendars, in honor of the resurrection of Jesus . Muslims observe their "day of congregation" , known as yaum al- jum`ah , on Friday because it

5092-430: The start of evening. This period of time sees human's highest body temperature , an increase of traffic collisions , and a decrease of productivity . Evening begins around 5 or 6 pm, or when the sun sets, and ends when one goes to bed. Twilight is the period before sunrise and after sunset in which there is natural light but no direct sunlight. The morning twilight begins at dawn and ends at sunrise, while

5168-473: The sun is visible. Light pollution during night can impact human and animal life, for example by disrupting sleep. Fortnight A fortnight is a unit of time equal to 14 days (two weeks ). The word derives from the Old English term fēowertīene niht , meaning " fourteen nights " (or "fourteen days", since the Anglo-Saxons counted by nights). In astronomy , a lunar fortnight

5244-523: The time of midnight varies between locations, time zones are set up to facilitate the use of a uniform standard time . Other conventions are sometimes used, for example the Jewish religious calendar counts days from sunset to sunset, so the Jewish Sabbath begins at sundown on Friday . In astronomy , a day begins at noon so that observations throughout a single night are recorded as happening on

5320-468: The universe by Allah. Abu Huraira reported that Muhammad said: Allah, the Exalted and Glorious, created the clay on Saturday and He created the mountains on Sunday and He created the trees on Monday and He created the things entailing labour on Tuesday and created light on Wednesday and He caused the animals to spread on Thursday and created Adam after 'Asr on Friday; the last creation at the last hour of

5396-458: The week are designated the first and the last, though virtually all have Saturday, Sunday or Monday as the first day. The Geneva -based ISO standards organization uses Monday as the first day of the week in its ISO week date system through the international ISO 8601 standard. Most of Europe and China consider Monday the first day of the (work) week, while North America, Israel, South Asia, and many Catholic and Protestant countries, consider Sunday

5472-611: Was adopted by the ancient Romans , but they later moved to a seven-day week, which had spread across Western Asia and the Eastern Mediterranean due to the influence of the Christian seven-day week, which is rooted in the Jewish seven-day week. In 321 CE, Emperor Constantine the Great officially decreed a seven-day week in the Roman Empire, including making Sunday a public holiday. This later spread across Europe, then

5548-473: Was apparently discussed in Plutarch in a treatise written in c. 100 CE, which is reported to have addressed the question of Why are the days named after the planets reckoned in a different order from the actual order? (the text of Plutarch's treatise has been lost). Dio Cassius (early 3rd century) gives two explanations in a section of his Historia Romana after mentioning the Jewish practice of sanctifying

5624-575: Was described as a sacred day of congregational worship in the Quran . The English word week comes from the Old English wice , ultimately from a Common Germanic * wikōn- , from a root * wik- "turn, move, change". The Germanic word probably had a wider meaning prior to the adoption of the Roman calendar , perhaps "succession series", as suggested by Gothic wikō translating taxis "order" in Luke 1:8. The seven-day week

5700-796: Was known in India by the 6th century, referenced in the Pañcasiddhāntikā . Shashi (2000) mentions the Garga Samhita , which he places in the 1st century BCE or CE, as a possible earlier reference to a seven-day week in India. He concludes "the above references furnish a terminus ad quem (viz. 1st century) The terminus a quo cannot be stated with certainty". The seven-day weekly cycle has remained unbroken in Christendom , and hence in Western history , for almost two millennia, despite changes to

5776-580: Was received by the Greeks in the 4th century BCE (notably via Eudoxus of Cnidus ). Although some sources, such as the Encyclopædia Britannica, state that the Babylonians named the days of the week after the five planets, the sun, and the moon, many scholars disagree. Eviatar Zerubavel says, "the establishment of a seven-day week based on the regular observance of the Sabbath is a distinctively Jewish contribution to civilization. The choice of

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