Why are there seven days in a week?

Your calendar dates back to Babylonian times.
Aleksandra Pikalova/Shutterstock.com

Kristin Heineman, Colorado State University

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to CuriousKidsUS@theconversation.com.

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Why are there seven days in a week? – Henry E., age 8, Somerville, Massachusetts

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Waiting for the weekend can often seem unbearable, a whole six days between Saturdays. Having seven days in a week has been the case for a very long time, and so people don’t often stop to ask why.

Most of our time reckoning is due to the movements of the planets, Moon and stars. Our day is equal to one full rotation of the Earth around its axis. Our year is a revolution of the Earth around the Sun, which takes 365 and ¼ days, which is why we add an extra day in February every four years, for a leap year.

But the week and the month are a bit trickier. The phases of the Moon do not exactly coincide with the solar calendar. The Moon cycle is 27 days and seven hours long, and there are 13 phases of the Moon in each solar year.

Some of the earliest civilizations observed the cosmos and recorded the movements of planets, the Sun and Moon. The Babylonians, who lived in modern-day Iraq, were astute observers and interpreters of the heavens, and it is largely thanks to them that our weeks are seven days long.

The reason they adopted the number seven was that they observed seven celestial bodies – the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn. So, that number held particular significance to them.

Other civilizations chose other numbers – like the Egyptians, whose week was 10 days long; or the Romans, whose week lasted eight.

Some of the earliest civilizations recorded the movements of planets, the Sun and Moon.
Andrey Prokhorov/Shutterstock.com

The Babylonians divided their lunar months into seven-day weeks, with the final day of the week holding particular religious significance. The 28-day month, or a complete cycle of the Moon, is a bit too large a period of time to manage effectively, and so the Babylonians divided their months into four equal parts of seven.

The number seven is not especially well-suited to coincide with the solar year, or even the months, so it did create a few inconsistencies.

However, the Babylonians were such a dominant culture in the Near East, especially in the sixth and seventh centuries B.C., that this, and many of their other notions of time – such as a 60-minute hour – persisted.

The seven-day week spread throughout the Near East. It was adopted by the Jews, who had been captives of the Babylonians at the height of that civilization’s power. Other cultures in the surrounding areas got on board with the seven-day week, including the Persian empire and the Greeks.

Centuries later, when Alexander the Great began to spread Greek culture throughout the Near East as far as India, the concept of the seven-day week spread as well. Scholars think that perhaps India later introduced the seven-day week to China.

Finally, once the Romans began to conquer the territory influenced by Alexander the Great, they too eventually shifted to the seven-day week. It was Emperor Constantine who decreed that the seven-day week was the official Roman week and made Sunday a public holiday in A.D. 321.

The weekend was not adopted until modern times in the 20th century. Although there have been some recent attempts to change the seven-day week, it has been around for so long that it seems like it is here to stay.

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This article has been updated to correct the details on Earth’s revolution around the Sun.

Kristin Heineman, Instructor in History, Colorado State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Explainer: the gods behind the days of the week

The Roman weekday ‘dies Veneris’ was named after the planet Venus, which in turn took its name from Venus, goddess of love. Detail from Venus and Mars, Botticelli, tempera on panel (c1483).
Wikimedia Commons

Margaret Clunies Ross, University of Sydney

The origins of our days of the week lie with the Romans. The Romans named their days of the week after the planets, which in turn were named after the Roman gods:

• dies Solis “the day of the sun (then considered a planet)”
• dies Lunae “the day of the moon”
• dies Martis, “the day of Mars”
• dies Mercurii, “the day of Mercury”
• dies Iovis, “the day of Jupiter”
• dies Veneris, “the day of Venus”
• dies Saturni, “the day of Saturn”

When the Germanic-speaking peoples of western Europe adopted the seven-day week, which was probably in the early centuries of the Christian era, they named their days after those of their own gods who were closest in attributes and character to the Roman deities.

It was one of those peoples, the Anglo-Saxons, that brought their gods and language (what would become English) to the British Isles during the fifth and sixth centuries AD.

Hendrik Goltzius, Mercury, oil on canvas (1611).
Wikimedia Commons

In English, Saturday, Sunday and Monday are named for Saturn, the sun and moon respectively, following the Latin.

The remaining four days (Tuesday, Wednesday, Thursday and Friday) are named for gods that the Anglo-Saxons probably worshipped before they migrated to England and during the short time before they converted to Christianity after that.

Tuesday is named for the god Tiw, about whom relatively little is known. Tiw was probably associated with warfare, just like the Roman god Mars.

Wednesday is named for the god Woden, who is paralleled with the Roman god Mercury, probably because both gods shared attributes of eloquence, the ability to travel, and the guardianship of the dead.

Thursday is Thunor’s day, or, to give the word its Old English form, Thunresdæg “the day of Thunder”. This sits beside the Latin dies Iovis, the day of Jove or Jupiter. Both of these gods are associated with thunder in their respective mythologies.

You may recognise a similarity here with the name of the famous Norse god Thor. This may be more than coincidence. Vikings arrived in England in the ninth century, bringing their own very similar gods with them. Anglo-Saxons were already Christian by this time, but may have recognised the similarity between the name of their ancestors’ deity Thunor and the Norse god. We don’t know, but the word Thor does appear in written texts from the period.

Chris Hemsworth as famous Norse god Thor in the 2011 film of the same name.
IMDB

Friday is the only weekday named for a female deity, Frig, who is hardly mentioned anywhere else in early English. The name does appear, however, as a common noun meaning “love, affection” in poetry. That is why Frig was chosen to pair with the Roman deity Venus, who was likewise associated with love and sex, and was commemorated in the Latin name for Friday.

Of gods and weekdays

The concept of the week, that is, a cycle of seven numbered or named days with one of them (usually Sunday or Monday) fixed as the first, was originally probably associated with the Jewish calendar. This was complicated by the fact that early medieval Europe inherited its idea of the week from imperial Rome, via the Christian church.

In early Christianity the reckoning of time was crucial to the proper celebration of the church’s feast days and holidays, especially the variable feast of Easter.

We find day names similar to English in related European languages, like Dutch, German, and all the Scandinavian or Norse languages. Gods with comparable names, like Tyr, Othinn, Thor and Frigg, were certainly known to the Scandinavians and gave their names to weekdays in Scandinavian languages (compare Modern Danish tisdag, onsdag, torsdag, fredag).

The Latin names for the days of the week, and the Roman gods for which they were named, still live on in all the European Romance languages, like French, Spanish and Italian. Think of French lundi, mardi, mercredi, jeudi and vendredi, for example, and you will find the Latin Luna, Mars, Mercurius, Iovis and Venus hidden behind them.

Margaret Clunies Ross, Eneritus Professor of English Language and Early English Literature, University of Sydney

This article was originally published on The Conversation. Read the original article.

How The Days Of The Week Got Their Name

The link below is to an article that looks at how the days of the week got their name.

For more visit:
http://www.theboredninja.com/featured/how-the-days-of-the-week-got-their-name/