Why the Week Has Seven Days

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…

• 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.”