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The Death and Life of the 13-Month Calendar (citylab.com)
136 points by skinofstars on Dec 12, 2014 | hide | past | web | favorite | 109 comments

"The International Fixed calendar sucked the personality out of marking time, making every week and month as predictable as humanly possible. [...] It's an impossible feat that doesn't need pulling off and, thankfully, no one is trying to anymore."

Spoken like someone who's never had to write date handling logic. Having "personality" in your calendar system is a bug, not a feature. I feel confident that we could maintain our overall levels of personality/joie de vivre/je ne sais quoi by spending less time dealing with an incredibly arbitrary calendar system and more time doing things we actually enjoy.

Yeah, it sucks the personality out of marking time like metric sucks the personality out of measuring space. I like personality in my dog and my friends, not in my systems of measurement.

Dates are almost impossible to reason about, and yet people are so used to our current broken system they aren't even aware of how badly they manage it. It is routine for date-time packages to produce bizarre results like "a month before a month from now" not being "today" in all cases because no one has any idea what anyone else means by "month", although everyone who has never thought about these problems is certain that everyone else means exactly what they mean in all ambiguous cases.

Anyone who has worked on date-time problems (not even libraries, just trying to correct for the special cases, cultural differences or just plain weirdness that the library of your choice doesn't deal with) will recognize the horrible truth of the joke, "I used to be in favour of space-travel, then I realized what effect it will have on date-time libraries."

> Anyone who has worked on date-time problems (not even libraries, just trying to correct for the special cases, cultural differences or just plain weirdness that the library of your choice doesn't deal with) will recognize the horrible truth of the joke, "I used to be in favour of space-travel, then I realized what effect it will have on date-time libraries."

...I think you just killed a piece of my soul... I understood that perfectly. :(

My favourite example of this is "tomorrow" because obviously, tomorrow is when you and I wake up the next day, NOT a minute past midnight.

Annoys me to no end that most calendar systems still don't understand that.

... perhaps it is telling: I can't figure out if you are being sarcastic or not. :/

In my head I keep a concept of "physical day" (real calendar days, followed by other, real calendar days) and "logical day", which is the day as I am currently experiencing or referring to it. If, after a long Monday, you're up past midnight (i.e, it is now Tuesday), then the "phyiscal" day is "Tuesday" and the logical day is "Monday". The logical day progresses either when you go to sleep (at which point one ends, and another begins when you wake), or at dawn.¹

Person to person speech is almost always in logical days; "tomorrow" would not be a minute past midnight in this system. This at least makes some things make sense.

¹There _still_ tons of issues with this, such as people who work at night and sleep during the day, people can be on different logical days, some places don't have a dawn for several months…

Not sure if you're being sarcastic or not.

If I said "the servers are down for maintenance at 2am tomorrow" when would you think they will be unavailable?

I wasn't being sarcastic at all.

If you said "2am tomorrow" I would assume two hours after next midnight. Perhaps this is a result of my usually late schedule because I normally go to bed around 2am, so everything up to then and including midnight is "tonight".

If I said "talk to me about it tomorrow" and later we're chatting at 1am, are you going to think I meant now?

A very small percentage of the population ever has to write date handling logic. For the rest, things "just work", thanks to those few.

Besides, even as a member of that small group, I like the variety of the current calendar, inefficient as it is.

One has to admit that it complicates even trivial communications about days and times. Even questions like "What's the date of friday next week?" can't be quickly answered. Or "Is Nov 12th on the weekend?" I feel these are practical things that _most_ people would _like_ to easily reason about, but can't.

It imperial units for days; or like trying to do math in a numerical system where each significant digit has a different random radix. Does it have variety? Yes... Is even remotely fun to do anything practical with? No.

Well, we already do math in a crazy-radix system for time, and the not-easily-divisible unitless variable of (1 year / 1 day) means that we can't do too much better -- we can reduce the problem to about one crazy radix, but no smaller; that radix will probably always depend on the value of the more-significant number in the date (the year).

But yes, we probably should quash the "variety is fun" argument early in the discussion. The problem is that it's a persistent low cost in the back of everyone's heads. Sure, when you think about it you might like it a lot, but it will then stress you out in hard-to-perceive ways during the rest of the year, with no real benefit to show for it.

The huge error that Eastman made was to keep the same month-names for the other months. This is a bad idea; if two systems are going to exist in parallel they need to be disambiguated in practice.

>The huge error that Eastman made was to keep the same month-names for the other months.

The problem is, you'll find, that naming things is an incredibly political act. Agreeing on a new name for anything is a terribly complicated process, and when you're talking about something every single person has a stake in... well, it would have never happened. He tried very skillfully to bypass all that, and basically succeeded.

No, his mistake was to underestimate the clout that religious tradition still had on large sectors of the ruling elites. Even now, when we pride ourself in the "scientificness" and rationality of our societies, we're still enslaved by stories written by agrarian priests at the dawn of civilization -- in many ways, it's worse now because nobody would even entertain proposals as bold as modernizing a system we've been using, almost unchanged, for two millennia, no matter how broken it might be.

Even questions like "What's the date of friday next week?" can't be quickly answered.

Fortunately we don't have a very pressing need to answer these sorts of questions; we have tools galore to handle them for us: smartphones, calendars, messaging apps, meetup etc. Topics like these often remind me of one of Einstein's more famous quotes:

[I do not] carry such information in my mind since it is readily available in books. ...The value of a college education is not the learning of many facts but the training of the mind to think.

We used to spend an enormous amount of time teaching our children mathematical tricks which have now all been made completely obsolete by the scientific calculator. Only the most rudimentary of arithmetical strategies have survived, if only for the fact that it's still a little inconvenient to reach into your pocket when scanning and counting objects with your eyes.

I disagree, many times people are trying to coordinate and one person says the 8th thinking it's a friday, but it's actually thursday. So some people think they were talking about the 8th, others talk about it like it were the 9th, and there's confusion all about.

Casual calendar coordination is really easy to mess up in the current state.

That quote is about memorizing a relatively arbitrary number (5,280 feet to a mile) which is only relevant when you have systems that can't be easily reasoned about.

This is precisely why the metric system, or uniform length of months, are useful.

> It imperial units for days

Imperial made quite a lot of sense when numbers were small and calculations done without the aid of instruments: Using bases divisible by both 3 and 4 makes mental calculation quite quick.

> Using bases divisible by both 3 and 4 makes mental calculation quite quick.

Easier than base 10?

Half a foot, six inches. Third of a foot, four inches. Quarter of a foot, three inches. Sixth, eighth, and twelfth also go into whole inches.

For bigger projects, yards are fairly easy to decompose too, into whole feet and inches.

It's a good system for projects of human or slightly super-human scale using low resolution instruments and mental math. It's rotten for high precision computerized tasks of widely varying scales.

I can't recall the last time I needed a third. Halves, quarters, tenths, hundredths...

You know, given that we have computers to perform the calculations, my own mad dream is to return to solar hours: twelve hours from sunrise to sunset, and twelve from sunset to sunrise. Thus summer hours would be longer and winter days would be shorter. Ditto minutes and seconds.

Science would of course need to have a standardised second almost always different from the current second, but that's no different from having a standardised temperature and pressure almost always different from the current temperature and pressure.

What on earth do you see the benefit of this as?

My theory is that living according to the sun is more natural and consequently more pleasant than living according to a metronome.

Someone's never written very many sql queries.

I'm pointing at you, tempestn.

An excellent video touching on some of the intractable aspects of our datetime-marking system's personality quirks: https://www.youtube.com/watch?v=-5wpm-gesOY

"I feel confident that we could maintain our overall levels of personality/joie de vivre/je ne sais quoi by spending less time dealing with an incredibly arbitrary calendar system and more time doing things we actually enjoy."

Backing your claim, I'd observe this is already a manifested fact. Consider holidays like Easter, which already are set by rules that have little to do with the calendar itself, and there's a number of such holidays floating about without any special problems of their own (above and beyond the problems of the calendar in general). The "personality" of the year is already independent of how we mark the time.

I've never felt any positive feelings towards any of the variances in how we keep time. "Oh golly gee, December's got a full 31 days, how exciting"

This. I have been thinking about this for a long time. Basically, 364 days are exactly the same, and what is currently December 31st would become the Year Day where everyone has it off. If it's a leap year, there'd be two Year Days. Simple, efficient, and easy to understand.

Birthdays being on the same day of the week is a poor objection: your birthday already falls on a weekday much more often then not, and chances are you celebrate it on the weekend before or after. We'd lose variability in holidays that are "last Thursday of the month": they'd just be on a specific date every year.

One nice thing we'd gain is that the phase of the moon would shift much slower with respect to our calendar (the moon doesn't do a Year Day). I suppose some superstitious healthcare workers might object to this. If you think about it, there are many more things naturally tied to 28 days than 28/30/31.

Actually the synodic month is closer to 365/12 days than to 28 days, so the 13-month calendar drifts slightly faster with respect to phases of the moon.

Fun fact:

The arabic calendar which is based on Moon movements used to have an extra month every four(?) years to adjust the season changes. It was called Nasi' month. But after a Quran Sura published that prohibited this month Arabic calendar lost it's accuracy for seasons.[1]

The Iranian Calendar that is based on sun movements was safe from this Sura because it didn't have an extra month but an extra day each five years.[2]

[1] http://en.wikipedia.org/wiki/Nasi%27

[2] http://en.wikipedia.org/wiki/Iranian_calendars

The Hebrew calendar (also lunar) still does this - a leap month in (IIRC) 7 out of every 19 years.

Eviatar Zerubavel's Seven Day Circle is a detailed and complex history of time telling.

It really helps to understand that in a calendar we're trying to measure three distinct (and variable) cycles, none of which fits precisely into the others, and each of which imposes its own rhythms on human life. Attempts to break each from the current 7/12/365 basis have virtually all failed.

The first is the Earth's rotation about its own axis -- different when measured with respect to the stars or the Sun.

The second is that of the Moon about Earth.

The third is of the Earth about the Sun.

We overlay them on each other and pick rough correspondences.

Much of the division has to do with Babylonian time reckoning, based on 360, and its factors: 2 * 2 * 2 * 3 * 3 * 5. From that you find 2, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 45, 72, 90, 180, and 360. A seven-day week doesn't fit this directly but is close (between 6 and 8), and a 30-day month also fits well.

Then you come to realize that all timekeeping, _especially_ that which picks a specific starting point, is arbitrary.

The book also details several attempts to change the system, particularly following the French and Russian revolutions (oh, and the reason for that being the October revolution -- and there's the question of what was the last nation to adopt the Gregorian calendar, and why the output of 'cal 1752' is what it is ... and why even _that_ is arbitrary (it depends on where you're specifying the date).


In New England (and likely elsewhere) you can see gravestones from the sixteen and seventeen hundreds that have two death dates on them, as different parts of the world converted to the Gregorian calendar at different times, and both Gregorian and Julian dates were in use in the area for a while (parts of Europe converted as early as the late 1500's).

It's not clear that the rotation of the moon has much significance in modern life any more, so maybe the problem can be simplified.

What was the significance of cycles of the moon in the past, anyway? The main thing I can think of is astrology. Can tides be predicted accurately using phases of the moon?

"What was the significance of cycles of the moon in the past?"

Really not my metier, but a few thoughts.

The Moon is highly significant if you're living along a coastline (and most humans do) as the tides are directly related.

In a pretechnological society, the biggest and cheapest source of night-time lighting was moonlight (though you could locally out-shine it with torches, candles, or lanterns). For travel or any sort of nocturnal activity (including ocean navigation), you'd likely take it into consideration.

In arctic cultures, moonlight might be your only light for much of the year, and on snow, full moonlight is amazingly brilliant.

In terms of dividing up the the year, different moons, particularly named moons ("hunters", "harvest", etc.) are significant.

Month = "Moonth"

Aside from the female menstrual cycle, the gestational cycle is also in line with the moon: A baby is brought to term in 10 moons or 280 days (9 months or so).

You would also have an easy way for disparate peoples to mark time, since in the past there was no such thing as telegraphs or even pony express.

That's only because we have a weird method for calculating pregnancies, for historical reasons.

A human pregnancy is around 266 days +- 16. The reason for 280 days or 9 months is because that measures the time span since the last menstruation, not since conception.

(I was personally a bit surprised by this when expecting our first child. It's one of those things you apparently know about but still use "9 months" as a bit of a fixed expression.)

> Aside from the female menstrual cycle

Birth control pills have a big effect on this now.

> A baby is brought to term in 10 moons or 280 days (9 months or so).

If you can't tell how far along a pregnancy is without reference to the Moon, there's no help for you.

It is extremely important in agriculture, which much of the world sustained, and sustains, itself on.

How is the moon's phases important in agriculture?

>How is the moon's phases important in agriculture?

traditional agriculture uses the moon to determine what to plant when.

i'm not saying this actually makes a difference (altho it might, considering the moon does influence sea levels and hence how water flows through the system), just that it's what agriculture is traditionally based on.

This seems to be slightly inferior to the Pax calendar[1].

The Pax calendar has another very cool property, which is that the weekdays are always in sync with Gregorian calendar. This is done by carrying over leapdays until you have one full week accumulated, which is then inserted as a leapweek, in the same way we insert leapdays in the Gregorian calendar.

[1] http://en.wikipedia.org/wiki/Pax_Calendar

Also in alternate calendars:

Each day in the Republican Calendar was divided into ten hours, each hour into 100 decimal minutes, and each decimal minute into 100 decimal seconds. Thus an hour was 144 conventional minutes (more than twice as long as a conventional hour), a minute was 86.4 conventional seconds (44% longer than a conventional minute), and a second was 0.864 conventional seconds (13.6% shorter than a conventional second).


When I was at Intel they marked everything in Work Weeks, that was essential for scheduling things like chip fabrication plants. It took a little while to get used to but then it made computing questions of 'when' quite straight forward.

I'm personally in favor of a more structured system like this, my wife on the other hand is viscerally opposed. If that schism is widespread I expect the next calender change to occur when the known world is ruled by an emperor :-)

"We've always done it this way" are the seven most expensive words in business. Catherine DeVrye (2000)

In addition to the 13 month calendar, I wish the year started in March or April. The beginning of Spring* makes more sense for a new year than the middle of winter.

*I realize this is only true in the northern hemisphere, but 90% of the world's population lives in the Northern Hemisphere. The other 10% can start their year in the Fall.

This is how the calendar originally worked (DECemeber is 10th month), until politics intervened in ancient Rome.

The Julian calendar typically started the year on the 25th of March (Lady Day) at noon (prior to clocks it was much easier to reckon mid-day than mid-night... navies kept this practice at least into the 1800's). This was true into the 1600's in parts of Europe and North America.

Given that the northward equinox is relevant to astronomy and geographic reference frames, I have also had occasions to wish that not only would the year start at that instant, but also that it be considered day 0 of the new year, rather than day 1.

Reading this article is my first exposure to this 13-month calendar [I don't count the Simpson's episode]. I'm glad for the read and found it very interesting.

This is a little bit different from the accounting 13 month calendar -- an "Adjustment" month that usually falls in the next FY that the accounting/auditors can do adjustments and still have 'true' dates on everything.

Honestly, having another month to pay bills (and you know that nobody's going to pro-rate everything down to 13 months) isn't really appealing right now, nor would the additional overhead of two more payroll cycles.

Logically, it makes sense, though.

For what it's worth, I'm already paid for 26 pay cycles each year, and I work at a company of 30k+.

This would complicate anything that is paid for monthly, including but not limited to: employee salaries, rent/mortgage, subscriptions, utilities, etc. Do we just ignore Sol for those purposes or roll it into another month?

Having your birthday perpetually on a wednesday would also not be so much fun. Perhaps "year day" could shift every year forward by 1 week day - year day could be Monday and then Jan 1 of the next year could be a Tuesday etc.

If we all switched to it, wouldn't it simplify all of those things?

Right now if you get paid every other week, you get paid 3 times in 2 months and twice in all the other months.

If you get paid twice a month on the 15th and last day of the month, payroll constantly has to take account of holidays and weekends because the day of the week is always fluctuating.

All of those things would have to change, but they would be simpler after the change. It's the same argument as switching to the metric system in the US. Unfortunately the fixed cost of having to switch outweighs the benefits of switching (certainly for the calendar, less so for metric).

Don't some companies already run salary in thirteen four week periods? I've worked at at least one that did.

I'm not 100% sure, but in the US, this is relatively rare, as it's required in most situations to be paid at least 2 times per month.

I think all but 5 states have laws dictating pay frequency, and in most cases they require at least two times a month pay frequency.

The most popular pay schedules tend to be 24, 26, and 52 times per year.

EDIT: This was supposed to be a reply to redblacktree. State law examples: - http://www.dir.ca.gov/dlse/faq_paydays.htm - http://labor.ny.gov/legal/counsel/pdf/frequency-of-pay-frequ...

I would like you to explain to me what the situation is in which you imagine that being paid every 2 weeks would result in you being paid less than twice a month.

> it's required in most situations to be paid at least 2 times per month.

Where did you get this? I have a friend who's paid monthly at his salaried software engineering gig.

Not 13, but I am paid in 26 two-week periods.

I got paid that way in CA for years. But that was 20 years ago.

Using the same calender every year might work fine in America and some of the Western European countries. (According to the article, Easter and Thanksgiving can be given fixed dates in the 13-month calendar.) But many non-Western cultures have holidays tied to phases of the moon. Chinese New Year would still move around a lot from year to year, making it impossible to reuse last year's calendar. Ditto for Chuseok in Korea, which needs to coincide with a full moon.

So yeah, this looks like a nice change, but it's not going to be completely static from year to year in every culture.

Besides, I don't think it will completely eliminate the difficulty of figuring out what date "next Thursday" is. We at HN tend to be mathematically competent, so we can easily calculate multiples of 7 in our heads and subtract a few without breaking a sweat. Most ordinary people, on the other hand, have difficulty figuring out what date next Monday is even when it's Friday and you just need to add 3. They'll just look it up in a paper calendar or their mobile device.

Okay, but can we come up with a calendar system where the months September, October, November, and December don't have the wrong names? It has always bothered me that the prefix sept- means seven, but it is the ninth month, oct- is for the tenth month, etc...

Those names are from when the calendar only had 10 months. They tacked on two months at the beginning.

In other fun facts, March is so named because that's when you go to war.

Have a 14-month year, then start the following year in March.

Sold. This could have the added benefit that every leap year we can get two days off for new years eve, since people will be used to getting Feb 28th off anyway ;)

There's also the ill-fated Soviet Revolutionary Calendar


And the similarly fated French Republican Calendar: http://en.wikipedia.org/wiki/French_Republican_Calendar

Somewhat related: the other day (this week even!) my wife was puzzled by the names of months and she asked me about the meaning of each. If you think about it for a moment you'll figure most of them out, but in any case this is a good summary: http://www.design.caltech.edu/erik/Misc/month_names.html

It's brilliant, I love it! That said, I'd be happy just to see the Daylight Saving time-switch left on the dustbin of history.

From the article:

> Easter would fall on April 15 every year on Cotsworth's calendar

I don't understand why this would be. Can someone explain?

I think that they're suggesting that this would be conventionally the case: "Okay, we're now deciding that Easter Sunday will be April 15, which is always a Sunday."

I think this is on the basis that it's important for Easter to be on a Sunday, and not nearly as important that it be the Sunday following the first full moon following the equinox, or whatever: just that once you say "it's got to be on a Sunday," you need some damn way to figure out which Sunday each year.

Easter is tied to the days of the week, it's always on a Sunday. So it's going to be week-aligned.

This calendar aligns months with weeks. Months are always exactly 4 weeks.

But Easter moves around quite a bit during the year, sometimes being on the 83rd day of the year (in 2008), sometimes on the 110th day of the year (2014), and various dates between. I don't see how changing to a 13 month calendar would affect the first full moon after the spring Equinox, since the lunar cycle doesn't mesh with the solar one.

> I don't see how changing to a 13 month calendar would affect the first full moon after the spring Equinox, since the lunar cycle doesn't mesh with the solar one.

Just checked... you seem to be correct. The lunar calendar isn't aligned with this well enough. While the equinox date is fixed, the first full moon after that should bounce around by several days at least. Even allowing that it's always the Sunday after that, it still seems as if it could fluctuate by a week in either direction.

See also the 'Synod of Whitby' (Whitby is also famous for Dracula - I'm not sure if that's related, but if you're a goth or easter-history fan it's a great place to visit! ;-) :


I love the idea of a 13 months calendar; however, you're birthday would be on the same day every year :0/.

Unless you were born Feb 29, I guess everyone's birthday is on the same day every year. Mine, for instance, is always on Sep 11, every single year.

You're confusing day (Monday, ...) with date (12th Dec).

He's pointing out that those stuck on a leap day are still stuck.

If you count by day-of-year when doing the conversion, though, it's the people born new year's eve on a leap year that are impacted.

Why do we even have a 7-day week?

7 and 28 are just as arbitrary as 12.

Why do we even have a solar year?

If the year was 100 days, we could have a whole year of summer.

Except that the year is based on the solar orbit, which has some quite obvious effects via the axial tilt causing seasons.

The month is based on the lunar orbits, which are a bit more arbitrary now and less important with an urban rather than agricultural economy, but still not completely arbitrary.

Weeks are a bit arbitrary, as far as we can tell, but very widespread and we seem to be stuck with them.

I'm always blown away by people who don't understand weeks.

A lunar month is 28 days.

There are few divisors of 28. 2, 4, 7, and 14 are the only ones. 28 days is too long for convenience if it's your shortest grouping of days. 2 days is too short. So, 4x7 or 7x4. Having 7 4 day weeks every month is probably a bit less convenient than 4 7 day weeks. Hence, 7 day weeks. (Or two 14 day weeks, which I think you essentially used to see some of the time: it seems like 17th-19th Century Britain was more aligned on fortnights than weeks).

Not NECESSARY in the same way that days are, but it's not exactly mysterious how they came about.

Edit: Oh, also, in terms of preferring 7 or 14 to 2 or 4, think about the lunar cycle. It easily breaks down into 7 or 14 day periods (7 days = new to half, or half to full, or full to half, or half to new. 14 days = new to full or full to new. 4 days = ?)

Edit2: Of course, a lunation (full moon to full moon) is 29.5 days, as opposed to the sidereal month (same part of sky to same part of sky) of 27.3 days. But I suspect that in antiquity, most people dealt with a conventional 28 days for both.

Weeks mostly have to do with the market cycle, which has been anywhere from 4 to ten days depending on the local economy. The Chinese in particular used 5 or 10 day weeks for quite some time. That works better for lunation than 7.

The seven day standard seems to have worked as a reasonable compromise across a wide variety of ancient economies and plan

You're not going to convince either the Christians or the Jews to do a week that isn't 7 days long. That number is more or less fixed by the sizeable minority who need it for the rest of their habits.

The solar year is convenient so that one can speak of "the average historical weather for this month" and such... but it's true that many others have done lunar calendars etc.

Muslims use the lunar calendar for religious occasions (Ramada, Hajj, Eid) but use the Christian, solar calendar (like the rest of the world) for everyday life.

The day and year are settled astronomically. As for the week, it's been in use for at least 2500 years continuously without ever skipping a day and now virtually every country uses it. The month, however, has variable length, has been redefined every thousand years or so, and has competing systems from Islam, Hindu, Jewish, Japanese and other cultures. The month can change, but the week never can.

That makes the extra day that isn't part of a week kind of problematic, doesn't it?

That does not make sense to have 100 days... it must follow the sun (day/night)

A week lasts for the duration of a moon phase.

I really like this idea - it makes scheduling things a whole lot easier. I also like the concepts of the one week month and "year day" - for some reason I feel like I'd get more pumped about year day than I'll ever get about new years.

I didn't see anything about a one-week month on there, but the diagrams sure make it look that way.

I wonder what Jews, Seventh Day Adventists, and Sabbatarians in general would think of this.

Lousy Smarch weather.

This makes more sense than switching to the metric system.

Why? I'm curious.

Mars Inc. uses 13-period calendar for everything.

When I worked for Royal Ahold they used a 13 period calendar. The date logic was much worse to manage because you still had the rest of the world and every programming language and database that used the Gregorian calendar.

We had a single mainframe subprogram that managed the whole thing. It was written in assembler and the few times it broke, the entire company stopped. Financials, ordering, invoicing, everything. Eventually they rewrote it in a more modern language, COBOL. This was in 2010.

My birthday would always be on a Sunday!

Did you check the day-month of your current birthday, or the day of the year? My birthday is April 8; that's the 98th day of the year (most years), which would be April 14 in the new calendar.

Also for the superstitious there would always be Friday the 13th

Easy fix, just start the month on a Monday instead of a Sunday

Starting the week on Monday seems more common than Sunday for most countries, I believe France does. And China and Japan name their days literally "Day 1" for Monday, ... "Day 6" for Saturday, and "Day Sun" for Sunday.

This is wrong. Saturday in Japanese is 土曜日, which is like "Earth day".

There's also "Sun day"(Sunday), "Moon day"(Monday), "Fire day"(Tuesday), "Water day"(Wednesday), "Tree day"(Thursday), "Gold day"(Friday), "Earth day"(Saturday). So your claim is wrong in Japanese for every day except Sunday.

If you see something written like 四日("4 day"), this refers to the day of the month not the day of the week(for Japanese).

Chinese uses the numbers for days of the week, so 星期一,星期二,星期三,星期四,星期五,星期六,星期日 for Monday to Sunday. They can use 周 or 礼拜 instead of 星期.

I remembered Japanese copied the Chinese at something there, but, whoops, it was the names of the planets that were copied. So the Chinese names of Mars(火星), Mercury(水星), Jupiter(木星), Venus(金星), and Saturn(土星) are copied onto the same days as planets that Romance languages name their days after.

FYI, 日 is not "seven". It's "sun" or "day". It's almost like someone had a sense of humor when they named that day.

My interpretation has always been that 日 is meant to represent "zero", but I never put any thought into why they didn't just call it 星期零.

"星期日" is generally written Chinese, but in speech Chinese say "星期天" where 天 could mean "God" when the 7-day week was copied from "Christian" Europe. I just found http://www.cjvlang.com/Dow/dowchin.html to explain the history of Chinese and Japanese day names in detail.

I've noticed while living in China that, whereas Westerners like me virtually always remember what day of week it is but often forget the date in the month, Chinese are more likely to remember the day of the month and forget the day of the week.

Ah. I grew up in a Cantonese-speaking Christian family in America, so I've never heard 星期天 used in speech at all.

Confusingly, the "seven luminaries" system in that article aren't just referencing the planets: they're also the names of Sun, Moon, Fire, Water, Wood, Metal, and Earth. I did get that sorted out by looking up Western alchemical ordering for the planets, which is in the same order. Wikipedia helpfully provides a table that includes the old names for the planets as well:


but then there would never be a Friday the 13th, which is also a problem. When would Hollywood release all its horror movies?

Won't somebody please think of the bikers!?

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