We didn't start the seven-day week cycle
January 14, 2016 8:19 AM   Subscribe

Why is today Thursday, rather than tomorrow or yesterday? I'm not asking why we have a seven day week; I'm asking whether we know how this specific cycle of seven days got started off. And, has it ever been interrupted?
posted by East Manitoba Regional Junior Kabaddi Champion '94 to Law & Government (7 answers total) 16 users marked this as a favorite
whether we know how this specific cycle of seven days got started off

There are a few (not necessarily mutually exclusive) theories, but there does not appear to be a definitive answer. You may be interested in the book The Seven Day Circle: The History and Meaning of the Week by Eviatar Zerubavel. Here's a NY Times review and summary.

has it ever been interrupted?

The French Republican Calendar shifted to a 10 day week for about 12 years.

But in general the days of the week operate independently of the calendar. For example, when England adopted the Gregorian calendar in 1750, "the calendar was advanced by 11 days: Wednesday 2 September 1752 was followed by Thursday 14 September 1752." Eleven calendar days were skipped, but the 7 day weekly cycle was uninterrupted.
posted by jedicus at 8:34 AM on January 14, 2016 [7 favorites]

Apparently the Babylonians added an extra day every month or so to keep their weeks in sync with the lunar cycles.

It sounds like nobody today knows for sure, but the Wikipedia article on the week does suggest which day was which didn't used to be completely arbitrary:
In a frequently-quoted suggestion going back to the early 20th century[by whom?] the Hebrew Sabbath is compared to the Sumerian sa-bat "mid-rest", a term for the full moon.
posted by aubilenon at 8:34 AM on January 14, 2016 [1 favorite]

Different days go back to different eras. And it's different in different languages. But all of it is pretty ancient. Actually the Wikipedia article is pretty good on this, if I understand what you are asking.
posted by beagle at 8:39 AM on January 14, 2016

According to Wikipedia, the current seven-day cycle dates back to the Roman empire, and has been unbroken since the year 311 AD or earlier.

The Roman empire officially adopted the seven-day week in 321 AD, but it had been in use since the first century AD. The naming of the days of the week was based on the planetary hours convention. There doesn’t seem to be any clear evidence of exactly when or how the start of the current unbroken cycle was determined.

The Roman seven-day week may be descended from the Babylonian calendar by way of the Greeks, Hebrews, and others. Babylonian months started on the day of the new crescent moon, and every seventh day from the new moon was a holy day. This means that cycle sometimes had to be broken by intercalary days to keep it in sync with the lunar cycle, which is not precisely 28 days. Originally this was done ad-hoc, based on observation of the moon. Then, starting around the year 500 BCE, the Babylonian calendar included intercalary days on a regular schedule based on the Metonic cycle (similar in concept to modern leap years).
posted by mbrubeck at 8:41 AM on January 14, 2016 [4 favorites]

It was sort-of interrupted in 1582 in Catholic countries (later in Protestant countries and Orthodox countries, and varying): "When the new calendar was put in use, the error accumulated in the 13 centuries since the Council of Nicaea was corrected by a deletion of 10 days. The Julian calendar day Thursday, 4 October 1582 was followed by the first day of the Gregorian calendar, Friday, 15 October 1582 (the cycle of weekdays was not affected)." Britain (and its American colonies), for example, didn't switch to the Gregorian calendar until 1752, so that George Washington was born under the Julian or "O.S." (old style) date system in 1731 and died under the Gregorian system in 1799.

The more-or-less current 7-day week system dates to the adoption of the Julian calendar in 45 BCE. The continuous 7-day cycle we currently use dates to Augustus, as far as we can tell, and " the first identifiable date cited complete with day of the week is 6 February 60, identified as a "Sunday" (as viii idus Februarius dies solis "eighth day before the ides of February, day of the Sun") in a Pompeiian graffito." (The graffito artist may not have known what day it was, though; it's a little unclear if two calendars were in play or if the dude couldn't tell time properly.)

The 7-day week itself probably comes from the observation that the lunar cycle is about 28 days, and many ancient calendars track their "weeks" onto that 28-day cycle and insert "leap days" at the end of a lunar month if they need to, to stay on track, and have the "week" start on the proper day of the next lunar month. We have preeeeeeetty good evidence that the Jews were using a continuous 7-day week during the Babylonian captivity (6th century BCE), which is maybe where you want to reach back to if you're looking for a continuous calendar as the Christian week that takes over Europe (and eventually the world) comes from the Jewish week and its Sabbath observations. But during the 1st century BCE and 1st century CE there's a lot of calendar changes going on as the Romans kind-of take charge of that sort of thing, so that's your really firm MODERN calendar start-point, with the Julian.
posted by Eyebrows McGee at 8:45 AM on January 14, 2016 [9 favorites]

FWIW, the names of the days of the week in Hebrew / on the Jewish calendar are literally "First Day," "Day 2" "Day 3" "Day 4", "Day 5", "Day 6" and "Sabbath".

Keeping the Sabbath day separate / holy is one of the most important tenets of the Torah, and one of the early differentiators of the Jewish people - so depending on what day you date the first Torah to (the earliest fragments found so far date to around 600 BCE), there is probably some correspondence with that as well - much earlier if you take into account that the first written torahs are believed to have come quite a bit later than the beginning of the oral tradition.

Sunday was changed to the Sabbath day rather than Saturday in 321 ACE by Emperor Constantine, but that only affected what day of the week was considered the Sabbath, it didn't rejigger the actual days of the week.
posted by Mchelly at 9:16 AM on January 14, 2016 [1 favorite]

In addition to the general astrological symbolism, it's important to remember that astrology used to be congruent with astronomy and math. 365 doesn't really work with any rational divisions (5, 73), but 364 divides equally into 13 cycles of 28 days, or 52 cycles of seven days. Part of why seven days feels natural is that it comes out pretty evenly, entirely as an accident of the cosmos.

366 comes out pretty evenly too, but in fewer rational groups — it factors down to (61, 6), (122, 3) and (183, 2).
posted by klangklangston at 2:01 PM on January 14, 2016 [1 favorite]

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