Week

A week is a unit of time equal to seven days. It is the standard time period used between a single day and a month in most parts of the world. There are just over 52 weeks in a year, or on average about 4 and a third weeks in a month. The days of the week are often used to organize work days, rest days, and special holy days. Sometimes, certain weeks are chosen for special purposes, like Golden Week in China and Japan, or awareness weeks such as National Family Week in Canada, which aim to highlight important topics.

Historically, not all cultures used a seven-day week. Some ancient cultures had weeks of different lengths, such as ten days in Egypt or an eight-day week for the Etruscans and ancient Romans. The seven-day week we use today began with the Romans, who named each day after a classical planet and its matching god. This idea mixed with the Jewish seven-day week, which centers on Saturday, and later with Christian traditions that honored Sunday (the day of the Resurrection of Christ). In AD 321, Emperor Constantine the Great made the seven-day week official in the Roman Empire, and it spread around the world from there.

In English, the names of the days come from a mix of Roman and Germanic traditions. For example, we have Sunday for the sun’s day, Monday for the moon’s day, and so on, ending with Saturday for Saturn’s day. Different cultures may start the week on different days, but almost all consider either Saturday, Sunday, or Monday to be the first day of the week.

The three major Abrahamic religions each have a special holy day during the week. Muslims hold their main worship day on Friday, as taught in the Quran. Jews rest and celebrate on Saturday, known as Shabbat, remembering God's rest after creating the world. Christians honor their holy day on Sunday, celebrating the resurrection of Jesus.

Name

The English word week comes from the Old English word wice, which is linked to an older Common Germanic root _*wikōn-. This root is related to the idea of "turn, move, change." Before the Roman calendar was adopted, the word might have meant something like "succession series," as seen in the Gothic word wikō used in Luke 1:8.

Many languages name the seven-day week using a word that means "seven." An old English word, sennight ("seven-night"), shows that people once counted time by nights, similar to the common word fortnight ("fourteen-night"). Words like hebdomad come from the Greek hebdomás, meaning "a seven." The term septimana shares roots with Romance languages from Latin [septimana], meaning "seven mornings."

Definition and duration

A week is a time period of exactly seven days. This means that one week has 168 hours, or 10,080 minutes, or 604,800 seconds.

In the Gregorian calendar, one year has 52 weeks plus one extra day, and two extra days in a leap year. The Moon’s path affects how we see weeks, making a week about 23.7% of a typical lunar cycle.

Days of the week

Main article: Names of the days of the week

"Days of the Week" redirects here. For the song, see Days of the Week (song).

The days of the week were named after the seven classical planets, which included the Sun and Moon. This naming system continued alongside a tradition of numbering the days in ecclesiastical Latin starting with Dominica (the Lord's Day) as the first day. The names of the days came from both Greco-Roman gods and Germanic traditions.

The order of the days does not follow the actual order of the planets. Instead, each day is named for a planet that is three places away in the traditional list. This special ordering was discussed by the writer Plutarch around 100 AD, though his writing on the topic has been lost. Dio Cassius from the early 3rd century also talked about this in his work.

A different way of numbering the days of the week was used in later times. This system influenced how some languages named the days, like calling Wednesday "mid-week" in Old High German. The ecclesiastical system is still used in Eastern Christianity, but in the Latin West it is only found in modern Icelandic, Galician, and Portuguese.

History

Ancient Near East

The earliest evidence of a seven-day period comes from a rule made by King Sargon of Akkad around 2300 BC. The Akkadians liked the number seven, and there were seven important objects in the sky that could be seen without special tools—the Sun, the Moon, and five planets.

Gudea, a leader and priest in Lagash in Sumer around 2100 BC, built a temple with seven rooms and celebrated a festival lasting seven days. In old stories from Assyro-Babylonian culture, like the Epic of Gilgamesh, storms lasted seven days, and important characters left their boats seven days after they landed.

The Babylonians counted days from the new moon and celebrated the 7th, 14th, 21st, and 28th days as special “holy” or “evil” days. These days had rules about what people could and could not do, and they were considered times to make offerings to gods.

Achaemenid Persia

The Zoroastrian calendar followed Babylonian ideas, linking the 7th, 14th, 21st, and 28th days of the month to Ahura Mazda. The system used in the Persian Empire came from the Babylonians and was used from the 4th century BC.

Judaism

A regular seven-day cycle, not tied to the Moon, began in Judaism by the 6th century BC at the latest.

There are different ideas about where the seven-day week came from in Jewish history.

Some believe it came from the Babylonians, who used days to match the Moon, but the Jewish week did not depend on the Moon.

Others think it came from the Jewish holy books or was a special idea of the Jewish people.

By the time of the Second Temple, Jews used the seven-day cycle with regular days of rest called Sabbaths.

Hellenistic and Roman era

Main article: Nundinae

The ancient Romans used an eight-day cycle. But after a new calendar started in 45 BC, the seven-day week became popular. People linked each day to objects in the sky like the Sun, Moon, and planets.

The seven-day week became common in the Roman Empire by the 1st century AD.

Islamic concept

In Islamic beliefs, the idea of a seven-day week began with the creation of the universe by Allah.

Adoption in Asia

China and Japan

The first known writing about a seven-day week in China is from Fan Ning in the late 4th century during the Jin dynasty. The idea spread to Japan in the 9th century and was used for special purposes until the Meiji Period (1868–1912), when it became a regular part of the calendar.

India

The seven-day week was known in India by the 6th century. Some think it may have been known even earlier, but this is not certain.

Christian Europe

Further information: Holy Week and Easter Week

The seven-day week has been used continuously in Christendom for nearly two thousand years. Special traditions and beliefs about lucky or unlucky days developed in the Middle Ages, especially around Friday and Sunday.

Numbering

Further information: Leap week calendar

In many places, weeks in a year are numbered. This is common in Europe and Asia but less so in the U.S. and other regions.

The ISO week date system, part of ISO 8601, is one way to number weeks. In this system, each week starts on Monday and is linked to the year that contains the week's Thursday.

For example, Week 1 of 2015 started on Monday, December 29, 2014, and ended on Sunday, January 4, 2015, because January 1, 2015, was a Thursday. Week 1 of 2021 started on Monday, January 4, 2021, and ended on Sunday, January 10, 2021, because January 1, 2021, was a Friday.

Some countries use different systems to number weeks. These systems may start the week on Saturday, Sunday, or Monday. Often, they agree on the week number for weekdays but can differ on weekends.

The epi week (epidemiological week) is used for reporting health data. It starts on Sunday and ends on Saturday. The first epi week of the year ends on the first Saturday of January, which may sometimes start in December of the previous year.

"Weeks" in other calendars

The word "week" can also describe other time periods that last a few days. Historically, different places have used "weeks" that last between four and ten days. Intervals longer than ten days are usually called something else, like a fortnight or a month.

Many old calendars had their own versions of weeks. For example, Ancient Rome used an eight-day week, and the ancient Chinese calendar had a ten-day week. Some cultures, like those in West Africa, used a six-day week, while others, such as the Javanese calendar, used a five-day week.

In some places, weeks were linked to market days. The Igbo people had a four-day market week, and the Aztecs and Mayas divided their calendars into weeks of 13 days.

Modern reforms

Further information: International Fixed Calendar, Decimal calendar, French Revolutionary Calendar § Ten days of the week, and Bahá'í calendar

Some modern calendars have tried new ways of organizing weeks. The International Fixed Calendar kept the seven-day week but arranged the year into 13 months of 28 days each. In Revolutionary France, a ten-day week called a décade was used for a short time. The Bahá'í calendar has a 19-day period that some consider a week.

Soviet

Further information: Soviet calendar

In the Soviet Union from 1929 to 1940, many workers used five or six-day work weeks instead of the usual seven-day week. The country still used the traditional seven-day week for most purposes.