NYT: Sunday All Over the World

By C. CLAIBORNE RAY

Q. Days, months and years are astronomically fixed, but weeks are not, so when and how did the days of the week get synchronized worldwide?

A. The seven-day week's origins are religious and social. Its beginnings are lost in the mists of time, but its timekeeping has long relied on astronomical expertise, and people got on the same calendar page as soon as they adopted the same modern calendar.

Religious historians say there is no reason to believe that the seven-day cycle of the Jewish week has been interrupted within historical memory, and they trace its origins at least to 1000 B.C. The seven-day Judeo-Christian-Roman week, adopted by the Roman emperor Constantine in A.D. 321, spread gradually around the world with conquest, colonization and commerce.

Western religious and civil authorities used all the resources of astronomy to keep track of the calendar and to ensure that Saturday was Saturday and Sunday was Sunday, no matter where. The Julian calendar reform of 1582 did not shift days of the week. Astronomical bases have been suggested for a seven-day division. Among them are the seven "planets" (including the sun, the moon and the five actual planets known to ancient civilizations) and the four phases of the moon in the lunar cycle of very roughly 28 days (which could also yield an eight-day week).

There were rival weeks, both ancient and modern, including short or long weeks corresponding to market days in some agricultural societies, 10-day weeks in revolutionary France and both five- and six-day weeks in Stalinist Russia.