Seven-day week
Encyclopedia
The seven-day week is used by the majority of the world and is the international standard
as specified in ISO 8601
.
by ancient cultures, including the Babylonian civilization and the Jewish religion. Jews celebrated every seventh day, within a continuous cycle of seven-day weeks, as a holy day of rest from their work; although it is possible that the Hebrew origin of the seven-day week was lunar, and not perpetual. Similarly, the Babylonians also celebrated the seventh day of each seven-day week as a holy day, but adjusted the number of days of the final week in their month so that their monthly calendar
would always commence on the new moon
. This may further be reflected in the contemporary and traditional Zoroastrian calendar
s that relates to the first, seventh and so on days of the month as pertaining to Ahura Mazda (God). Historically, a number of other major religio-cultural groups, such as Christians and Muslims, have continued to regularly hold religious events on a specific day within each seven-day week.
The seven-day week is approximately a quarter of a lunation
, so it has been proposed that this is the implicit, astronomical origin of the seven-day week. However, there are a number of problems with this proposal. The seven-day week is actually only 23.7% of a lunation, which means that a continuous cycle of seven-day weeks rapidly loses synchronisation with the lunation. This problem is compounded by the fact that a lunation is only the mean
time for the lunar phase
cycle, with each individual lunar phase varying in length. Also, the duodecimal
(base-12) and sexagesimal (base-60) numeral systems have historically been the primary systems used to divide other chronological and calendar units. Therefore, it is not immediately apparent why the seven-day week was selected by ancient cultures, rather than a week that included a number of days that was a factor of these numeral systems, such as a six-day or a twelve-day week, or a week that divided the lunation more accurately using a factor of these number systems, such as a five-day or ten-day week. Finally, there are no historical Jewish or Babylonian records that confirm that these cultures explicitly defined the seven-day week as a quarter of a lunation.
Counting from the new moon
, the Babylonians celebrated the 7th, 14th, 21st, and 28th as "holy-days", also called "evil days" (meaning "unsuitable" for prohibited activities). On these days officials were prohibited from various activities and common men were forbidden to "make 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. Tablets from the sixth-century B.C. reigns of Cyrus the Great
and Cambyses
indicate these dates were sometimes approximate. 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. Further, reconstruction of a broken tablet seems to define the rarely attested Sapattum or Sabattum as the 15th day of the lunation: this word is cognate with Hebrew Shabbat
, but is monthly rather than weekly; it is regarded as a form of Sumer
ian sa-bat ("mid-rest"), attested in Akkadian
as um nuh libbi ("day of mid-repose").
A seven-day week is mentioned in the Creation story
contained in the Book of Genesis, in the Hebrew Bible
, where Yahowah (God) is said to have created the heavens and the earth in six days and rested on the seventh . Also, in the Book of Exodus, the fourth of the ten commandments
is to rest on the seventh day, the Sabbath
, which can be seen as implicating a seven-day week social institution .
in the 6th century BCE, after the destruction of the Temple of Solomon.
The ancient Romans traditionally used the eight-day nundinal cycle, but after the adoption of the Julian calendar
, in the time of Augustus
, the seven-day week came into use. For a while, the week and the nundinal cycle coexisted, but by the time the week was officially adopted by Constantine in AD 321
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 the naked eye dates to the Roman era (2nd century).
, 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 AD.
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
).
discontinued the seven-day week for a ten-day week with the introduction of the republican calendar
in 1793. The Concordat of 1801
, which re-established the Roman Catholic Church
in France, also restored the seven-day week, beginning with Easter Sunday, 18 April 1802.
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.
, although according to Pandurang Vaman Kane
author of History of Dharmasastra
"this is not conclusive".
The Pañcasiddhāntikā mentions 'Monday'. The Garga
dated 1st Century BCE, refers to the seven-day week, Sunday to Saturday.
He concludes "the above references furnish a terminus ad quem (viz. 1st century BCE–1st century CE) The terminus a quo
cannot be stated with certainty".
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 is either 52 or 53 (it was 53 for year 2004). Schematically, this ISO convention translates as follows:
In some countries, though, the numbering system is different from the ISO standard. At least six numberings are in use:
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, which cannot be represented by a finite decimal expansion). There are exactly 20871 weeks in 400 Gregorian years, so 30 April 1611 was a Saturday just like 30 April 2011.
A system of Dominical letter
s has been used to determine the day of week in the Gregorian
or the Julian calendar
.
International standard
International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...
as specified in ISO 8601
ISO 8601
ISO 8601 Data elements and interchange formats – Information interchange – Representation of dates and times is an international standard covering the exchange of date and time-related data. It was issued by the International Organization for Standardization and was first published in 1988...
.
Origins
The origin of the seven-day week is the religious significance that was placed on the seventh daySeventh day
The seventh day may refer to:*Saturday in some calendars*Sunday in other calendars*Friday in the Bahá'í calendar*Shabbat in Judaism*Sabbath in seventh-day churches*The 7th Day, a 2004 Spanish film*Qixi Festival, a Chinese festival...
by ancient cultures, including the Babylonian civilization and the Jewish religion. Jews celebrated every seventh day, within a continuous cycle of seven-day weeks, as a holy day of rest from their work; although it is possible that the Hebrew origin of the seven-day week was lunar, and not perpetual. Similarly, the Babylonians also celebrated the seventh day of each seven-day week as a holy day, but adjusted the number of days of the final week in their month so that their monthly calendar
Calendar
A calendar is a system of organizing days for social, religious, commercial, or administrative purposes. This is done by giving names to periods of time, typically days, weeks, months, and years. The name given to each day is known as a date. Periods in a calendar are usually, though not...
would always commence on the new moon
New moon
In astronomical terminology, the new moon is the lunar phase that occurs when the Moon, in its monthly orbital motion around Earth, lies between Earth and the Sun, and is therefore in conjunction with the Sun as seen from Earth...
. This may further be reflected in the contemporary and traditional Zoroastrian calendar
Zoroastrian calendar
This article treats of the reckoning of days, months and years in the calendar used by adherents of the Zoroastrian faith. Zoroastrian religious festivals are discussed elsewhere, but have a fixed relationship to Nawruz, the New Year festival, whose timing is discussed below...
s that relates to the first, seventh and so on days of the month as pertaining to Ahura Mazda (God). Historically, a number of other major religio-cultural groups, such as Christians and Muslims, have continued to regularly hold religious events on a specific day within each seven-day week.
The seven-day week is approximately a quarter of a lunation
Lunation
Lunation is the mean time for one lunar phase cycle . It is on average 29.530589 days, or 29 days 12 hours 44 minutes and 3 seconds...
, so it has been proposed that this is the implicit, astronomical origin of the seven-day week. However, there are a number of problems with this proposal. The seven-day week is actually only 23.7% of a lunation, which means that a continuous cycle of seven-day weeks rapidly loses synchronisation with the lunation. This problem is compounded by the fact that a lunation is only the mean
Mean
In statistics, mean has two related meanings:* the arithmetic mean .* the expected value of a random variable, which is also called the population mean....
time for the lunar phase
Lunar phase
A lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...
cycle, with each individual lunar phase varying in length. Also, the duodecimal
Duodecimal
The duodecimal system is a positional notation numeral system using twelve as its base. In this system, the number ten may be written as 'A', 'T' or 'X', and the number eleven as 'B' or 'E'...
(base-12) and sexagesimal (base-60) numeral systems have historically been the primary systems used to divide other chronological and calendar units. Therefore, it is not immediately apparent why the seven-day week was selected by ancient cultures, rather than a week that included a number of days that was a factor of these numeral systems, such as a six-day or a twelve-day week, or a week that divided the lunation more accurately using a factor of these number systems, such as a five-day or ten-day week. Finally, there are no historical Jewish or Babylonian records that confirm that these cultures explicitly defined the seven-day week as a quarter of a lunation.
Ancient Near East
Counting from the new moon
New moon
In astronomical terminology, the new moon is the lunar phase that occurs when the Moon, in its monthly orbital motion around Earth, lies between Earth and the Sun, and is therefore in conjunction with the Sun as seen from Earth...
, the Babylonians celebrated the 7th, 14th, 21st, and 28th as "holy-days", also called "evil days" (meaning "unsuitable" for prohibited activities). On these days officials were prohibited from various activities and common men were forbidden to "make 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. Tablets from the sixth-century B.C. reigns of Cyrus the Great
Cyrus the Great
Cyrus II of Persia , commonly known as Cyrus the Great, also known as Cyrus the Elder, was the founder of the Achaemenid Empire. Under his rule, the empire embraced all the previous civilized states of the ancient Near East, expanded vastly and eventually conquered most of Southwest Asia and much...
and Cambyses
Cambyses
Cambyses can refer to two ancient rulers and two plays:-*Cambyses I, King of Anshan 600 to 559 BCE*Cambyses II, King of Persia 530 to 522 BCE*Cambyses, a tragedy by Thomas Preston...
indicate these dates were sometimes approximate. The lunation
Lunation
Lunation is the mean time for one lunar phase cycle . It is on average 29.530589 days, or 29 days 12 hours 44 minutes and 3 seconds...
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. Further, reconstruction of a broken tablet seems to define the rarely attested Sapattum or Sabattum as the 15th day of the lunation: this word is cognate with Hebrew Shabbat
Shabbat
Shabbat is the seventh day of the Jewish week and a day of rest in Judaism. Shabbat is observed from a few minutes before sunset on Friday evening until a few minutes after when one would expect to be able to see three stars in the sky on Saturday night. The exact times, therefore, differ from...
, but is monthly rather than weekly; it is regarded as a form of Sumer
Sumer
Sumer was a civilization and historical region in southern Mesopotamia, modern Iraq during the Chalcolithic and Early Bronze Age....
ian sa-bat ("mid-rest"), attested in Akkadian
Akkadian language
Akkadian is an extinct Semitic language that was spoken in ancient Mesopotamia. The earliest attested Semitic language, it used the cuneiform writing system derived ultimately from ancient Sumerian, an unrelated language isolate...
as um nuh libbi ("day of mid-repose").
A seven-day week is mentioned in the Creation story
Creation according to Genesis
The Genesis creation narrative describes the divine creation of the world including the first man and woman...
contained in the Book of Genesis, in the Hebrew Bible
Hebrew Bible
The Hebrew Bible is a term used by biblical scholars outside of Judaism to refer to the Tanakh , a canonical collection of Jewish texts, and the common textual antecedent of the several canonical editions of the Christian Old Testament...
, where Yahowah (God) is said to have created the heavens and the earth in six days and rested on the seventh . Also, in the Book of Exodus, the fourth of the ten commandments
Ten Commandments
The Ten Commandments, also known as the Decalogue , are a set of biblical principles relating to ethics and worship, which play a fundamental role in Judaism and most forms of Christianity. They include instructions to worship only God and to keep the Sabbath, and prohibitions against idolatry,...
is to rest on the seventh day, the Sabbath
Biblical Sabbath
Sabbath in the Bible is usually a weekly day of rest and time of worship. The Sabbath is first mentioned in the Genesis creation narrative. The seventh day is there set aside as a day of rest—the Sabbath. It is observed differently in Judaism and Christianity and informs a similar occasion in...
, which can be seen as implicating a seven-day week social institution .
Classical Antiquity
Frank C. Senn in his book Christian Liturgy: Catholic and Evangelical points to data suggesting evidence of an early continuous use of a seven-day week; referring to the Jews during the Babylonian CaptivityBabylonian captivity
The Babylonian captivity was the period in Jewish history during which the Jews of the ancient Kingdom of Judah were captives in Babylon—conventionally 587–538 BCE....
in the 6th century BCE, after the destruction of the Temple of Solomon.
The ancient Romans traditionally used the eight-day nundinal cycle, but after the adoption of the Julian calendar
Julian calendar
The Julian calendar began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year .The Julian calendar has a regular year of 365 days divided into 12 months...
, in the time of Augustus
Augustus
Augustus ;23 September 63 BC – 19 August AD 14) is considered the first emperor of the Roman Empire, which he ruled alone from 27 BC until his death in 14 AD.The dates of his rule are contemporary dates; Augustus lived under two calendars, the Roman Republican until 45 BC, and the Julian...
, the seven-day week came into use. For a while, the week and the nundinal cycle coexisted, but by the time the week was officially adopted by Constantine in AD 321
321
Year 321 was a common year starting on Sunday of the Julian calendar. At the time, it was known as the Year of the Consulship of Crispus and Constantinus...
the nundinal cycle had fallen out of use.
The association of the days of the week
Days of the week
The names of the days of the week from the Roman period have been both named after the seven planets of classical astronomy and numbered, beginning with Monday. In Slavic languages, a numbering system was adopted, but beginning with Monday. There was an even older tradition of names in Ancient...
with the Sun, the Moon, and the five planets visible to the naked eye dates to the Roman era (2nd century).
Christian Europe
The seven-day weekly cycle is reputed to have remained unbroken in Europe for almost two millennia, despite changes to the Alexandrian, JulianJulian calendar
The Julian calendar began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year .The Julian calendar has a regular year of 365 days divided into 12 months...
, and Gregorian
Gregorian calendar
The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter...
calendars.
The date of Easter
Easter
Easter is the central feast in the Christian liturgical year. According to the Canonical gospels, Jesus rose from the dead on the third day after his crucifixion. His resurrection is celebrated on Easter Day or Easter Sunday...
Sunday can be traced back through numerous computistic tables
Computus
Computus is the calculation of the date of Easter in the Christian calendar. The name has been used for this procedure since the early Middle Ages, as it was one of the most important computations of the age....
to an Ethiopic copy of an early Alexandrian table beginning with the Easter of 311 AD.
China
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 ManichaeansManichaeism
Manichaeism in Modern Persian Āyin e Māni; ) was one of the major Iranian Gnostic religions, originating in Sassanid Persia.Although most of the original writings of the founding prophet Mani have been lost, numerous translations and fragmentary texts have survived...
are documented with the writings of the Chinese Buddhist monk Yi Jing
I Ching (monk)
Yijing was a Tang Dynasty Chinese Buddhist monk, originally named Zhang Wenming . The written records of his travels contributed to the world knowledge of the ancient kingdom of Srivijaya, as well as providing information about the other kingdoms lying on the route between China and the Nālandā...
and the Ceylonese or Central Asian Buddhist monk Bu Kong
Amoghavajra
Amoghavajra was a prolific translator who became one of the most politically powerful Buddhist monks in Chinese history, acknowledged as one of the eight patriarchs of the doctrine in Shingon lineages.-Life:Born in Samarkand of an Indian father and Sogdian mother, he went...
of the 7th century (Tang Dynasty
Tang Dynasty
The Tang Dynasty was an imperial dynasty of China preceded by the Sui Dynasty and followed by the Five Dynasties and Ten Kingdoms Period. It was founded by the Li family, who seized power during the decline and collapse of the Sui Empire...
).
France
FranceFrance
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
discontinued the seven-day week for a ten-day week with the introduction of the republican calendar
French Republican Calendar
The French Republican Calendar or French Revolutionary Calendar was a calendar created and implemented during the French Revolution, and used by the French government for about 12 years from late 1793 to 1805, and for 18 days by the Paris Commune in 1871...
in 1793. The Concordat of 1801
Concordat of 1801
The Concordat of 1801 was an agreement between Napoleon and Pope Pius VII, signed on 15 July 1801. It solidified the Roman Catholic Church as the majority church of France and brought back most of its civil status....
, which re-established the Roman Catholic Church
Roman Catholic Church
The Catholic Church, also known as the Roman Catholic Church, is the world's largest Christian church, with over a billion members. Led by the Pope, it defines its mission as spreading the gospel of Jesus Christ, administering the sacraments and exercising charity...
in France, also restored the seven-day week, beginning with Easter Sunday, 18 April 1802.
Japan
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 HeianHeian period
The is the last division of classical Japanese history, running from 794 to 1185. The period is named after the capital city of Heian-kyō, or modern Kyōto. It is the period in Japanese history when Buddhism, Taoism and other Chinese influences were at their height...
Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
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
Meiji period
The , also known as the Meiji era, is a Japanese era which extended from September 1868 through July 1912. This period represents the first half of the Empire of Japan.- Meiji Restoration and the emperor :...
era.
Hindu
The seven-day week may have been in use during the Vedic PeriodVedic period
The Vedic period was a period in history during which the Vedas, the oldest scriptures of Hinduism, were composed. The time span of the period is uncertain. Philological and linguistic evidence indicates that the Rigveda, the oldest of the Vedas, was composed roughly between 1700–1100 BCE, also...
, although according to Pandurang Vaman Kane
Pandurang Vaman Kane
Bharat Ratna Dr. Pandurang Vaman Kane was a notable Indologist and Sanskrit scholar. He received India's highest civilian award Bharat Ratna in 1963. He was born in a conservative Chitpavan Brahmin family in the Ratnagiri district in Maharashtra, India. Eminent Historian Professor R.S...
author of History of Dharmasastra
History of Dharmasastra (book)
History of Dharmasastra, with subtitle Ancient and Medieval Religious and Civil Law in India, is a monumental five-volume work, consisting of around 6,500 pages, and was written by Dr. Pandurang Vaman Kane, an indologist. The first volume of the work was published in 1930 and the last one in 1962....
"this is not conclusive".
The Pañcasiddhāntikā mentions 'Monday'. The Garga
Garga Samhita
Garga Samhita is a book written by the sage Garga and deals with the life of Krishna. This Garga Samhita is different from the astrological treatise with the same name Garga Samhita. Only fragments of the astrological text with the name Garga samhita is available; but the whole of the devotional...
dated 1st Century BCE, refers to the seven-day week, Sunday to Saturday.
He concludes "the above references furnish a terminus ad quem (viz. 1st century BCE–1st century CE) The terminus a quo
Terminus post quem
Terminus post quem and terminus ante quem specify approximate dates for events...
cannot be stated with certainty".
Soviet Union
In 1929 USSR discontinued the seven-day week for a five-day week, then a six-day week. While the days were still named according to the seven-day week, the work schedules were rotated in five- and six-day periods. The seven-day week was reintroduced on 27 June 1940.Week numbering
Weeks in a Gregorian calendar year can be numbered for each year. This style of numbering is commonly used (for example, by schools and businesses) in some European and Asian countries, but rare elsewhere.ISO 8601
ISO 8601
ISO 8601 Data elements and interchange formats – Information interchange – Representation of dates and times is an international standard covering the exchange of date and time-related data. It was issued by the International Organization for Standardization and was first published in 1988...
includes the ISO week date
ISO week date
The ISO week date system is a leap week calendar system that is part of the ISO 8601 date and time standard. The system is used in government and business for fiscal years, as well as in timekeeping....
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 is either 52 or 53 (it was 53 for year 2004). Schematically, this ISO convention translates as follows:
| Dates in January | Effect | |||||||
|---|---|---|---|---|---|---|---|---|
| M | T | W | T | F | S | S | Week number | Week assigned to |
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 1 | New year |
| 1 | 2 | 3 | 4 | 5 | 6 | 1 | New year | |
| 1 | 2 | 3 | 4 | 5 | 1 | New year | ||
| 1 | 2 | 3 | 4 | 1 | New year | |||
| 1 | 2 | 3 | 52 or 53 | Previous year | ||||
| 1 | 2 | 52 or 53 | Previous year | |||||
| 1 | 52 or 53 | Previous year |
In some countries, though, the numbering system is different from the ISO standard. At least six numberings are in use:
| First day of week | First week of year contains | Weeks assigned twice | Used by/in | ||
|---|---|---|---|---|---|
| Monday Monday Monday is the day of the week between Sunday and Tuesday. According to international standard ISO 8601 it is the first day of the work week. According to the Islamic and Hebrew calendars, Sunday is the first day of the week... |
no | Most of Europe and countries adhering to ISO 8601 ISO 8601 ISO 8601 Data elements and interchange formats – Information interchange – Representation of dates and times is an international standard covering the exchange of date and time-related data. It was issued by the International Organization for Standardization and was first published in 1988... |
|||
| Saturday Saturday Saturday is the day of the week following Friday and preceding Sunday.Saturday is the last day of the week on many calendars and in conventions that consider the week as beginning on Sunday, or the sixth day of the week according to international standard ISO 8601 which was first published in... |
yes | Much of the Middle East | |||
| Sunday Sunday Sunday is the day of the week between Saturday and Monday. For most Christians, Sunday is observed as a day for worship of God and rest, due to the belief that it is Lord's Day, the day of Christ's resurrection.... |
yes | Canada, USA, Mexico |
Facts and figures
- 1 week = 7 days = 168 hours = 10,080 minutes = 604,800 seconds (except at daylight saving timeDaylight saving timeDaylight saving time —also summer time in several countries including in British English and European official terminology —is the practice of temporarily advancing clocks during the summertime so that afternoons have more daylight and mornings have less...
transitions or leap seconds) - 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
Gregorian calendar
The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter...
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, which cannot be represented by a finite decimal expansion). There are exactly 20871 weeks in 400 Gregorian years, so 30 April 1611 was a Saturday just like 30 April 2011.
A system of Dominical letter
Dominical letter
Dominical letters are letters A, B, C, D, E, F and G assigned to days in a cycle of seven with the letter A always set against 1 January as an aid for finding the day of the week of a given calendar date and in calculating Easter....
s has been used to determine the day of week in the Gregorian
Gregorian calendar
The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter...
or the Julian calendar
Julian calendar
The Julian calendar began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year .The Julian calendar has a regular year of 365 days divided into 12 months...
.
See also
- Calculating the day of the weekCalculating the day of the weekThis article details various mathematical algorithms to calculate the day of the week for any particular date in the past or future.A typical application is to calculate the day of the week on which someone was born or some other special event occurred....
- Dominical letterDominical letterDominical letters are letters A, B, C, D, E, F and G assigned to days in a cycle of seven with the letter A always set against 1 January as an aid for finding the day of the week of a given calendar date and in calculating Easter....
- WorkweekWorkweekThe workweek and weekend are those complementary parts of the week devoted to labour and rest respectively. The legal working week , or workweek , is the part of the seven-day week devoted to labor. In most Western countries it is Monday to Friday. The weekend comprises the two traditionally...
- Hebrew calendarHebrew calendarThe Hebrew calendar , or Jewish calendar, is a lunisolar calendar used today predominantly for Jewish religious observances. It determines the dates for Jewish holidays and the appropriate public reading of Torah portions, yahrzeits , and daily Psalm reading, among many ceremonial uses...
- Broadcast calendarBroadcast calendarThe broadcast calendar is a standardized calendar used primarily for the planning and purchase of radio and television programs and advertising. Every week in the broadcast calendar starts on a Monday and ends on a Sunday, and every month has either four or five such weeks...
- Lunar phaseLunar phaseA lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...
External links
- Week Wheel for Children