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The Week

by Vincent Mallette
Copyright © 1999 Inwit Publishing, Inc.

Next to the day, the week is the most important calendric unit in our life. And yet, there is no astronomical significance to the week. Nothing cosmic happens in the heavens in seven days.1 How, then, did the week come to assume such importance?

The first thing to understand is that a week is not necessarily seven days. In pre-literate societies, weeks of 4 to 10 days were observed; those weeks were typically the interval from one market day to the next. Four to 10 days gave farmers enough time to accumulate and transport goods to sell. (The one week that was almost always avoided was the 7-day week — it was considered unlucky!) The 7-day week was introduced in Rome (where ides, nones, and calends were the vogue) in the first century A.D. by Persian astrologists, not by Christians or Jews as is commonly thought. The idea was that there would be a day for the five known planets plus the sun and the moon, making seven; this was an ancient West Asian idea. However, when Christianity became the official religion of the Roman empire in the time of Constantine (c. 325 A.D.), the familiar Hebrew-Christian week of 7 days, beginning on Sunday, became combined with the pagan week and took its place in the Julian calendar. Thereafter, the week now observed in Rome appeared seamless with the 7-day week of the Bible — even though its pagan roots were obvious in the names of the days: Saturn's day, Sun's day, Moon's day. The other days take their equally pagan names in English from a detour into Norse mythology: Tiw's day, Woden's day, Thor's day, and Fria's day.

The amazing thing is that today the 7-day week, which is widely viewed as being Judeo-Christian, holds sway for civil purposes over the entire world. Chinese, Arabs, Indians, Africans, Japanese, and a hundred others sit down at the U.N. to the tune of a 7-day week, in perfect peace (at least calendrically!). So dear is this succession of 7 days that when the calendar changed from Julian to Gregorian the week was preserved, though not the days of the month: in 1752, in England, Sept. 14 followed Sept. 2 — but Thursday followed Wednesday, as always. Eleven days disappeared from the calendar — but not from the week!

1 Yes, it's true that the average time from, say, half-moon to full moon is 7.383 days, but this is less than 12% closer to 7 than to 8. (Possibly mindful of this, the Romans had an 8-day week.) In any case, the exact moment of half or full moon is hard to judge. The moon determines the month, not the week (the very word "month" has been related to "moon" for thousands of years; in Sanskrit they are the same.)

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