Days and Weeks

The Winged Chariot of Time

Days

The measure of day length is obvious. It is simply the time required for our old planet to spin around once on its axis with respect to the sun. Our natural and 24-hour days match almost exactly. Even so, deciding when the day begins is at the same time both arbitrary and according to custom.

During the eighth century B.C., Babylonian astronomers (known as Chaldeans) began their day when the sun was at its highest point in the sky. Like theirs, our own astronomical day is from noon to noon.

Other early peoples believed that the current day ended and a new one began either when the sun rose or when it set. Beginning the day either at sunrise or sunset was a good choice, but there is a fault with this manner of fixing when a day begins: the elapsed time of daylight (and darkness) constantly changes from one day to the next. We allude to this fact when we remark in springtime that the days are getting longer, or in the fall, shorter.

As a result, early peoples who divided daylight into a fixed number of segments found that the length of their hours varied throughout the year. On the other hand, there's also a downside to beginning the day other than at some easily observable solar position—it is necessary to have a precise means to measure the passing of time.

Weeks

Every society has either invented the week or copied it from others. A time unit longer than a day but smaller than a month is essential to human affairs. It was originally intended to set aside special days for recurring activities such as worship and marketing. Weeks of early peoples were not of the same length, but varied from one area to another.

Many primitive cultures used a four-day week, possibly in honor of the four directions. Central American peoples used a five day interval; Assyrians had a six day period; preChristian Romans had periods of eight days called nundinae. For many centuries, ancient Greeks—like Babylonians and Egyptians of the same period—divided their 30-day months into three "decades" of ten days.

Observation of the sky, in addition to originally fixing the beginning of a day, also resulted in determining the length of our weeks. It stems from an ancient and interesting tradition. If you care to read about it, select Origin of the Seven-Day Week from Footnotes.

Prior to and for some time after Julius Caesar, Roman Calendars included repeating cycles of letters A thru H to represent their eight-day marketing week. These were independent of monthly divisions called Calends, Nones and Ides. At the end of each year the A thru H cycle was broken. The first day of the next year was always designated by the letter "A" to begin a new cycle, but the market day's letter itself changed.

But weeks are not now an official part of the Gregorian Calendar. In order to understand why, consider the following:

When Caesar extended the year of 46 B.C. to 445 days and made other calendar changes, the Roman eight-day week was not affected. Of course, that cycle did change and remained unbroken after the seven-day period was officially adopted by Constantine in A.D. 321. But neither month nor year lengths were modified when Constantine reduced the Roman weekly cycle's length by a day.

We know that when Pope Gregory XIII eliminated ten days from October of 1582, Thursday the 4th was followed by Friday the 15th. ⁴ A similar continuation of the weekly cycle occurred in 1752 at the time Great Britain and its American colonies dropped eleven days from their calendar upon switching from Julian to Gregorian.

A search of the Inter Gravissimas bull (Pope Gregory's calendar specification) reveals no mention of the week. Neither are Latin names for its days mentioned in IG. Even the day to celebrate Easter is referred to in its Article 6 not as Sunday (Dies Solis in Latin) but rather as diem dominium, which translates as "the lord's day." IG does acknowledge the week's existence, but only in this obtuse manner. Neither week length nor the names of its days are specified, though a seven-day period was certainly assumed.

International Organization for Standardization number ISO 8601 specifies a date notation of YYYY-MM-DD. YYYY is the calendar year, MM is the Gregorian month between 01 and 12, and DD is the day of the month from 01 thru 31. Not only are weeks omitted from this notation, but a completely separate specification is used to designate them.

All of the above demonstrates that weeks are not an official part of our calendar. But for practical purposes, just as early Romans did, we superimpose weekly periods upon graphic representations of calendar months.

The cycle of weeks and our Gregorian Calendar are two separate but parallel and overlapping methods used to mark the passing of time.