Why does a week have seven days?

The Backwards Man

And other random questions that have just occurred to you?

Seriously though, whoy?

wiki wiki

ThisRegard

If you paid attention in school you'd know.

TheBully

Even though it would be perfectly possible to imagine a week having five, six or even eleven days, most cultures in the world have seven-day weeks. The reason for this is that seven celestial bodies were known to the ancients: the Sun, the Moon, Mars, Mercury, Jupiter, Venus and Saturn.

The Backwards Man

TheBully wrote: »

Even though it would be perfectly possible to imagine a week having five, six or even eleven days, most cultures in the world have seven-day weeks. The reason for this is that seven celestial bodies were known to the ancients: the Sun, the Moon, Mars, Mercury, Jupiter, Venus and Saturn.

But how did the know they were celestial bodies? All it would take is one Messopotamian having a stye in their eye and tomorrow would be thuednesday. . .

TallGlass

Why isn't time and date metric !

The Backwards Man

TallGlass wrote: »

Why isn't time and date metric !

Time and date is like an old deaf donkey we used to have when I was wee, you could call it whatever you want but it just carried on regardless

quickbeam

The Backwards Man wrote: »

And other random questions that have just occurred to you?

Seriously though, whoy?

One week lasts one phase of the moon. 4 phases = 1 month.

osarusan

It didn't always. The Babylonians started a cycle of 4 weeks on new moons and had holy days on every 7th day, but needed a 4th week of 8 or 9 days to get back to a new moon again.

seamus

The Backwards Man wrote: »

But how did the know they were celestial bodies? All it would take is one Messopotamian having a stye in their eye and tomorrow would be thuednesday. . .

These are the ones you can see with the naked eye. Because they don't always appear and don't appear in the same places all the time, they knew there was something special about these seven.
The ordering apparently is something to do with how fast they move across the sky, thus the week starting with the sun, then the moon, etc.

TallGlass

TallGlass wrote: »

Why isn't time and date metric !

A ten day week would be a real pain if you only had a two day weekend.

Hammer89

****ing magnets, how do they work?

The Backwards Man

seamus wrote: »

These are the ones you can see with the naked eye. Because they don't always appear and don't appear in the same places all the time, they knew there was something special about these seven.
The ordering apparently is something to do with how fast they move across the sky, thus the week starting with the sun, then the moon, etc.

Would that not mean antipodean cultures would have had the days mixed up though?

mzungu

The Backwards Man wrote: »

And other random questions that have just occurred to you?

Seriously though, whoy?

The number seven had a mystical significance to Babylonians. It was associated with the seven heavenly bodies; the Sun, Moon, Mars, Mercury, Jupiter, Venus and Saturn.

For this reason, some believe, marking rituals every seventh-day became important. A seven-day week based on these same celestial bodies was adopted as far away as Japan and ancient China.

Seven is also important in Judaism, where the creation story is told over seven days. But unlike other cultures, in Hebrew the days of the week are assigned numbers not the names of gods, festivals, elements or planets - the only exception is Saturday, Yom Shabbat (יום שבת) which means Sabbath.

But the popularity of the seven-day week - and its prominence in modern calendars - can be traced to its adoption by the Romans.

They named the days of the week after the pagan gods of Rome, the Sun and the Moon.

Roman Emperor Constantine formally adopted the seven-day week in AD 321, it had been in use informally since the first century BC. A Christian convert Constantine made Sunday - the Christian Sabbath - the first day of the week, and Saturday - the Jewish day of rest - as the last.

Link: http://www.bbc.co.uk/religion/0/20394641

quickbeam

The Backwards Man wrote: »

Would that not mean antipodean cultures would have had the days mixed up though?

Because all the planets orbit the sun roughly in a plane, they'd be seen by both northern and southern cultures - they basically follow the path of the constellations that make up the zodiac - no further north than the Tropic of Cancer and no further south than the Tropic of Capricorn.

The Backwards Man

quickbeam wrote: »

Because all the planets orbit the sun roughly in a plane, they'd be seen by both northern and southern cultures - they basically follow the path of the constellations that make up the zodiac - no further north than the Tropic of Cancer and no further south than the Tropic of Capricorn.

Ah, learn something new every day! Thanks!

Duckworth_Luas

TallGlass wrote: »

Why isn't time and date metric !

After the French Revolution they attempted to introduce 10 day weeks but it was rejected as even the most ardent revolutionaries did not want to work 8 days.

Esel

What is the stars, Joxer?

Ted111

Jupiter has a seven day week. And so does the Sun.
So it can't all be a coincidence.

Graces7

The Backwards Man wrote: »

And other random questions that have just occurred to you?

Seriously though, whoy?

Why not?

Peregrinus

TheBully wrote: »

Even though it would be perfectly possible to imagine a week having five, six or even eleven days, most cultures in the world have seven-day weeks. The reason for this is that seven celestial bodies were known to the ancients: the Sun, the Moon, Mars, Mercury, Jupiter, Venus and Saturn.

This explains why the seven days have the names they do, but it doesn't explain why have seven days in the first place, since there is no absolute need to name the days after celestial bodies.

The reason is the one quickbeam points to; the seven-day week is a a convenient division of the lunar month, though as orusan points out it does require adjustment with the insertion of extra days to keep the weeks and months in phase. In the modern calendar we don't do this, which is why any day of the month can fall on any day of the week.

TallGlass asks why the calendar isn't metricated. There have been attempts, most famously during the French Revolution, when a calendar with a ten-day week was introduced (as well as 10-hour days, 100-minute hours and 100-second minutes. But the brutal facts of science are that neither the solar year nor the lunar month are a convenient multiple of ten days, and while a decimal calendar makes calculations easier it does result in a disconnect between the calendar and the cycle of seasons that it measures. Decimalisation has to stop at some point; the revolutionary calendar had 12 months, not 10, plus 5 or 6 "complementary days" to try and keep in phase with the solar year. This feature naturally meant that simplification of calculation didn't extend to periods of more than a year, and while in any given year each month would start on the same day of the week, in the following year each month would start on a different day of the week.

It all seemed like a lot of trouble for very little benefit, plus the workers were angry at having only 3 rest days, instead of 4 or 5, in each month. It was introduced in 1793 but various elements of it were dropped between 1801 and 1806, when the whole thing was dropped. The 7-day week, I think, was restored in 1802.

Mellor

The Backwards Man wrote: »

Would that not mean antipodean cultures would have had the days mixed up though?

Well no, because even if their positions are inverted, their speeds don't change. The sun still moves fastest, then the moon, etc.

More importantly, the currently calendar is based on a system created by one culture, that spread to other cultures. Antipodeans probably didn't divide their time based on celestial bodies.

Ted111 wrote: »

Jupiter has a seven day week. And so does the Sun.
So it can't all be a coincidence.

There are no weeks on other planets. I'm not sure what you are thinking of.

Peregrinus

Mellor wrote: »

Well no, because even if their positions are inverted, their speeds don't change. The sun still moves fastest, then the moon, etc.

More importantly, the currently calendar is based on a system created by one culture, that spread to other cultures. Antipodeans probably didn't divide their time based on celestial bodies.

Pretty much all cultures divide time based on the seasons, and their signficance for agriculture, hunting, etc. While there are different seasons in different parts of the world, they all work on a one-year cycle, for obvious reasons, so pretty much all cultures develop a calendar in which the solar year is a central element.

The Babylonians found observing the heavenly bodies to be a convenient and reliable way of measuring the passage of the seasons, and they built his into their calendar. (The fact that they also imagined the gods to be in the heavens probably helped.) But this doesn't have to be so; the French revolutionary calendar, already mentioned, had twelve months which were named after the weather conditions or agricultural phenomena or activities expected to characterise that time of year. (But the ten days of the revolutionary week had the distinctly unimaginative names of first day, second day, third day, etc.)

Indigenous Australian cultures developed a variety of calendars reflecting the seasons in different parts of Australia. They could certainly have used the movements of celestial bodies to measure the passage of time, but I don't know if any of them did. Mostly the months/seasons were named after phenomena that would be important to hunter/gatherer cultures, and the passage of time was marked not by observing the positions or movements of the heavenly bodies, but by observing the immediate environment - the ghost gums are flowering, the Zamia is fruiting, Bunuru has begun, it's time to move down to the coast because the fishing will be good.

In some cases months/seasons had two names, on set referring directly to botanical or zoological phenomena and the other referring to some natural cycle applied figuratively to the months of the year. The six months of the Noongar calendar, for example, are named for childhood, adolescence, adulthood, fertility, conception, birth.

In other parts of Australia the local people have calendars of two season, three seasons, five seasons, or anything up to 13 seasons.

Mellor

Peregrinus wrote: »

Pretty much all cultures divide time based on the seasons, and their signficance for agriculture, hunting, etc. While there are different seasons in different parts of the world, they all work on a one-year cycle, for obvious reasons, so pretty much all cultures develop a calendar in which the solar year is a central element.

The Babylonians found observing the heavenly bodies to be a convenient and reliable way of measuring the passage of the seasons, and they built his into their calendar. (The fact that they also imagined the gods to be in the heavens probably helped.) But this doesn't have to be so; the French revolutionary calendar, already mentioned, had twelve months which were named after the weather conditions or agricultural phenomena or activities expected to characterise that time of year. (But the ten days of the revolutionary week had the distinctly unimaginative names of first day, second day, third day, etc.)

Indigenous Australian cultures developed a variety of calendars reflecting the seasons in different parts of Australia. They could certainly have used the movements of celestial bodies to measure the passage of time, but I don't know if any of them did. Mostly the months/seasons were named after phenomena that would be important to hunter/gatherer cultures, and the passage of time was marked not by observing the positions or movements of the heavenly bodies, but by observing the immediate environment - the ghost gums are flowering, the Zamia is fruiting, Bunuru has begun, it's time to move down to the coast because the fishing will be good.

In some cases months/seasons had two names, on set referring directly to botanical or zoological phenomena and the other referring to some natural cycle applied figuratively to the months of the year. The six months of the Noongar calendar, for example, are named for childhood, adolescence, adulthood, fertility, conception, birth.

In other parts of Australia the local people have calendars of two season, three seasons, five seasons, or anything up to 13 seasons.

That's all well and good but the thread is about weeks not seasons.

The point was, it's irrelevant that celestial bodies are inverted in the southern hemisphere (the point raised) as the Indigenous Australians, for example, didn't name days after the celestial bodies as the Babylonians did.
They were aware of the lunar cycle. The moon-man growing fat and lazy, then then having chunks axed off him by his wives. But afaik they didn't have weeks. Just days and seasons.

Indigenous Australians did track times of the year by celestial bodies though. When certain constellations appeared, it signalled certain animals would be giving birth, or fish would migrate certain areas. Other movements and appearances became the official start of winter (or equivalent). Of course this varied from tribe to tribe, and location to location. It's a big place.

seamus

Peregrinus wrote: »

The reason is the one quickbeam points to; the seven-day week is a a convenient division of the lunar month, though as orusan points out it does require adjustment with the insertion of extra days to keep the weeks and months in phase. In the modern calendar we don't do this, which is why any day of the month can fall on any day of the week.

4 weeks in a month, 7 days in a week, 13 months. 13 * 28 = 364.

Have a single day every year that doesn't "exist" and it's a party day - it's the last day of the year and doesn't have a weekday designation. The day before it is Sunday, the day after it is Monday. Two of them every four years.

Much simpler system.

MadDog76

Does pregnancy last 9 months (36 weeks) or 40 weeks (10 months)???

Boom_Bap

Because this song would be ridiculous if there were only 6 days.

https://www.youtube.com/watch?v=EeSLHJvsg_w

LordSutch

The Backwards Man wrote: »

Why does a week have seven days?

And other random questions that have just occurred to you?

Seriously though, whoy?

Why does water freeze? why does spring follow winter? why does paper burn?

quickbeam

MadDog76 wrote: »

Does pregnancy last 9 months (36 weeks) or 40 weeks (10 months)???

40 weeks on average, but that's not 10 months.

52 weeks and 12 months in a year
1/4 of a year is 13 weeks and 3 months
3/4 of a year is 39 weeks and 9 months

40 weeks of pregnancy is 9 months + 1 week.

sbsquarepants

MadDog76 wrote: »

Does pregnancy last 9 months (36 weeks) or 40 weeks (10 months)???

If a month was only 4 weeks, there'd have to be 13 of them in a year.

biko

What happens to matter that is sucked into a black hole?