Why a week is seven days?

[GLM4475]

I know this is a stupid question

and maybe some of you don't really care

if a week is 5, 6, or 10 days. But really, I'm curious.

Is there a deep history behind this

or is it just an archaic men's whim?

[Ceris]

http://lmgtfy.com/?q=why+is+a+week+7+days

[Fiddle]

Wikipedia gives a basic overview of the matter:

While the seven-day cycle may have deep historical origins in the Ancient Near East, the "planetary theory" of horoscopy is a development of Babylonian astrology roughly around 500 BC, with the oldest extant horoscope dated to just before 400 BC.^[6]

The seven-day week being approximately a quarter of a lunation has been proposed (e.g. by Friedrich Delitzsch) as the implicit, astronomical origin of the seven-day week,^[7] and indeed the Babylonian calendar used intercalary days to synchronize the last week of a month with the new moon.^[8]

The seven-day week seems to have been adopted (independently) by the Persian Empire, in Judaism and in Hellenistic astrology, and (via Greek transmission) in Gupta India and Tang China.^[9] The Babylonian system was received by the Greeks in the 4th century BC (notably via Eudoxus of Cnidus). But the designation of the seven days of the week to the seven planets does not seem to have any Babylonian precedent^[10] and is rather an original innovation of Hellenistic astrology, probably first conceived in the 2nd century BC.^[6] It was widely known throughout the Roman Empire by the 1st century AD, and ultimately replaced the older Roman system of the nundinal cycle during the 4th century.

[Stray Cat]

It was done based on the cycles of the moon. 

 

The Babylonian's realized that there was about 7 days per quarter cycle of the moon.  Thus, the 7th day or each quarter was a "holy-day", and 4 of these comprised a full lunar cycle.  

 

Of course, this was not perfect and was adjusted over the years to get the system we have today. 

[Eclipsed]

A bunch of caveman got together and notice that earth is square and moon never shows its backside

Then Galileo proved aliens exist

~~
idk never thought about it nor care to Google about it

i do know the basic 1 day is earth rotation, 1 month is moon orbit earth, and 1 year is earth orbit sun (approx, of course)

edit: oh that makes sense. each week is a quarter moon cycle then if 4 weeks = 1 month

[GLM4475]

Hmm, lunar cycle eh? I see.