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Why the Week Has Seven Days

Catherine Boeckmann
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No more logic supports seven days than, say eight or five, yet the seven-day week has resisted any and all attempt at change.

Unlike the year and the month, which correspond to the movements of the earth around the sun and the moon around the earth, the week has no astronomical analogue. Seven days is roughly the same length of a phase of the moon (seven days, nine hours) but any system of timekeeping quickly falls apart due to the extra hours piling up.

Officially adopted by the Emperor Constantine in A.D. 321, the seven-day week goes back thousands of years. Here’s some history…

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  • The seven-day week started with the first civilizations of the Middle East. Mesopotamian astrologers designated one day for each of the seven most prominent objects in the sky—the Sun, the Moon, and the five major planets visible to the naked eye.
  • The Jews also adopted a seven-day cycle, based on the time it took the Lord to create the universe as reported in Genesis. A new wrinkle in their week was the Sabbath, a day set aside for rest. This was the first time a culture had invented a holiday that occurred on a regular basis, unrelated to natural phenomena.
  • The Romans adopted different weeks for business reasons; they thought of a week as the 8 days between market days.
  • West African societies preferred a four-day market cycle.
  • In Assyria, 6 days was the rule; in Egypt, 10; in China; 15.
  • The ancient Germans used a five-day cycle named for their primary gods which is how our week ended up honoring Norse deities like Tiw (Tuesday), Odin (Wednesday), Thor (Thursday), and Frigga (Friday). Our word “week” may come from the Old Norse word vikja, which means “to turn.” Sunday and Monday, or course, honor the Sun and the Moon.

Atheistic revolutionaries tried, unsuccessfully, to get rid of the seven-day week. In 1793 the leaders of the French Revolution produced a new calendar divided into three ten-day “decades.” It never caught on, and Napoleon abandoned it in 1805.

In 1929 the Soviet Union tried a five-day week, with one day of rest.

  • Instead of the traditional day names, the days were given colors: yellow, orange, red, purple, and green.
  • In order to keep mass production going, each Soviet citizen was assigned a different day of rest, so that a husband might have a yellow day off, while his wife took her leisure on green.
  • Due to mass confusion, the plan was revised in 1932 to a six-day week, with numbers replacing the colors.
  • By 1940, the Russians were back on the familiar seven-day cycle!

Somebody was always trying to come up with something better! In 1936 the League of Nations solicited proposals for world calendar reform and considered almost 200 different schemes, many of which rearranged the week.

  • Edward Skille of Drummund, Wisconsin, suggested a year consisting of 73 five-day weeks called “metos.” The days of the week would be called Ano, Beno, Ceno, Deno, and Eno.

Why the seven-day week? It doesn’t divide evenly into 365- or 366-day years, so that holidays fall on different days of the week from year to year. But human beings are not logical creatures. Who can imagine saying, “What are you doing next purple?” or “Yeah, it’s Eno!”

As one member of the British Parliament remarked in a 1944 debate on calendar reform, “It is bad enough to be born on April 1, but to have one’s birthday always on a Monday would be perfectly intolerable.”

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About The Author

Catherine Boeckmann

Catherine Boeckmann loves nature, stargazing, and gardening so it’s not surprising that she and The Old Farmer’s Almanac found each other. She leads digital content for the Almanac website, and is also a certified master gardener in the state of Indiana. Read More from Catherine Boeckmann
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Ken (not verified)

2 weeks 5 days ago

Hi!

Question: you mentioned that the ancient Germans had a 5 day week but then only named 4 Norse deities. Who was the 5th? You did mention the Sun & Moon, but that takes the tally to 6. (Or have I missed something?)

Also, I was wondering what names Constantine used in 321 AD? Were the Norse-derived names in common use by then or did that come later?

I also wonder if there’s a neurological argument for choosing 7 over 10? Perhaps tracking 10 days past or hence is too taxing? A Goldilocks situation, ie a cycle not too short nor long? OTOH, perhaps the brain adapts to the system under which it develops?

I learned many weeks ago that the Japanese had a time system which had a fixed number of variable length hours. That is, every day had 12 hours of light & dark but the length of each hour changed with the seasons. A perfectly reasonable solution, imho, with its own pros and cons. But it also suggests other ways to divide the year, eg variable length weeks.

Hi Ken, and thanks for both the questions and the info.

As for the missing day in the Germanic lineup, Saturday was omitted because the inspiration was not a Norse god, but rather the Roman god Saturn. We’ve got a bit more on the origin of the names of the the days of the week at https://www.almanac.com/origin-day-names.

As for the days as defined by Constantine, our friends at the Merriam-Webster Dictionary explain his system of naming after celestial bodies: https://www.merriam-webster.com/wordplay/etymologies-for-every-day-of-the-week#:~:text=In%20the%204th%20century%20AD,seven%20days%20of%20the%20week.

When it comes to the length of the week and why seven days finally won out, your guess is as good as ours. I like the Goldilocks idea as much as anything else. Seven days is not too much and not too little. Perhaps that made it just right.

 

Brian (Imani) (not verified)

2 years 1 month ago

Could it be that the antiquity of the 7 day week, lays in the fact that is was originally observed when archaic humanity followed only a lunar calendar. With the 7 days observed and followed to mark the four Lunar phases in its monthly cycle.

Yes! Exactly! 7 + 7 + 7 + 7 = 1 Lunar Cycle of 28 Daze! And 4 = "Them"! Thee "Fore" Sevens ("Weaks") IN Each & EVEry "Won" Of Them (months)... "Their" ARE 4 "Horsemen" or 4 Arch Angels. PregNancy AND Birth! "Four" ALL IT's Worth! Life! Coming! IN TOO! Death AND Dying. Good? "Ore" Evil? To "Be"? Or "Knot"!

Ronald John (not verified)

3 years 9 months ago

The biblical book of Genesis does indeed record God creating the universe. It is interesting to note that, in the holy scriptures, when the Hebrew word yom is used in connection with reference to night time, it means a twenty-four hour day. When yom is used in connection to a reference to day time, it also means a twenty-four hour day. So, in Genesis chapters one and two, when Moses, by inspiration of the Holy Spirit, used the word yom in reference to night AND day, it absolutely means a twenty-four hour day. God created the universe in six literal days, and He did no work on the seventh day, because His work of creation from the beginning was "good" and "ended" . This sets a pattern for everyone to work, but to set aside a day of rest. Thank you.

Val (not verified)

6 years 3 months ago

I do not think there was ever meant to be a calendar set any precise way. It was dark before light, this is called night. Then there was day when the sun rose and then set. That is one day. No day is the same length they are ever changing. So from that we should be calling a day cycle from set of sun, to rise of sun. Not a time on a clock such as 12 pm to 00:01 am That is why we have Leap year and Daylight savings time to fix the mess made for a set time for a day. I would say we should go to that for the days and see what happens. That is how was meant to be I believe. Then there were Signs and Seasons for the rest of the things we needed to know.

You have no understanding of the derivation of the numerical system for timekeeping of the days nor do you understand the calendar and cause for leap years. You are completely wrong. You need to educate yourself.

L Maunder (not verified)

10 years 11 months ago

"In the beginning God created the heavens and the earth."( Genesis 1:1) . This opening statement of the Bible stands alone, indicating no distinct period of time related to the creation of "the heavens and the earth."( A reference to the entire universe) From verse 2 onward, Genesis chapter one discusses the six creative 'days' during which God evidently prepared the-already-existing-earth for human habitation. These six creative 'days' could have lasted for thousands of years. The Bible account of creation, thus, does not conflict with scientific conclusions about the age of the universe. [Compare Genesis 2:4 for the figurative use of the word "day."]

Your mention of Earth being Gods place to put creation asserts a gap that God couldn't do Creation in 6 days, and then take a rest. The Bible says, evening and morning and it was the 1st day. So the earth was rotating, and in that 24 hour period, we have evening and morning. Jesus did not need 'gaps' for His creation, He is God, all knowing and able to speak creation into existence, 'Is Genesis History' video series explains it all very well, very well. Also, the rest on the 7th day shows man that he will need a rest, we are not God, but we need rest, and God put in place a 'holiday' to allow reflection and worship toward a perfect God so we could give glory to the God who deserves it.

The 24 hour day, was not created until the Sun was made on the fourth day. Therefore, the first 3 days were not 24 hours.