More on calendars

When this post goes up, it will be the start of 2016. A new year. Time to throw out those old calendars and set up the new ones. (Well, probably not. Most people just use the calendars on their computers or phones these days.) But before you toss that record of the old year, take a look at it, because it’s actually quite interesting.

A couple of weeks ago, I talked about holidays. This time around, I’m going to look at the whole calendar. Not just our own, mind you, but others throughout history and the modern world. Some of them have features that might be useful to a writer looking to make his fantasy world distinctive.

Into the west

Let’s start with our familiar western calendar. It’s the simplest, but only because we’re familiar with it; if we grew up using, say, the Islamic calendar, then we would be used to that. Now, you already know the basics, if you’re above the age of 4. The year is divided into twelve months, beginning in January and ending in December. Months have fixed numbers of days, but they aren’t the same: we’ve got four of them with 30 days, seven with 31, and then February, which can have 29 in leap years (like this one), but normally has 28.

Months can then be divided into weeks of 7 days each (though only February divides exactly). Days, of course, are 24 hours long, not counting Daylight Saving Time, and hours are subdivided into 60 minutes, which are, in turn, subdivided into 60 seconds. Going back to the other end, years are counted from the putative birth of Christ, with the only real nod to religious diversity being the “modern” names for either side of the dividing line: Christian Era (CE) and Before Christian Era (BCE) versus the traditional Anno Domini (AD) and Before Christ (BC). We can also group the years into decades, centuries, and millennia, but these are more a notational convenience than a function of the calendar.

So that’s what the Western calendar is. But why is it like that? Why are the months uneven? Why does the year start in January? Do we really need leap years?

Let’s start with the first question there. Our calendar is the result of a long chain of cause and effect reaching far back into history, but its current form was largely determined by the Romans. They were the ones that gave us our twelve months, with essentially today’s names. As usual, though, it’s not that simple.

First off, the Roman (Julian, technically; Julius Caesar’s reign saw more than its share of calendar reforms) New Year was in March, so January and February were at the end of the calendar. February 29, the leap day, would have been the last day on the list. The year starting in March basically lasted until the Gregorian reform: sometime since 1582, depending on where you live. (In America, the one time a non-specialist would encounter the Julian-to-Gregorian switchover is in genealogy. Some dates in the 18th century—when Britain and the colonies that would become the US switched—are recorded as OS or NS. These stand for Old Style and New Style, meaning what we now call the Julian and Gregorian calendars, respectively.)

Incidentally, moving the year’s starting date messed up the naming. September comes from the Latin word for “seven”, which you wouldn’t expect from the ninth month. But a few hundred years ago, it would have been linguistically accurate. The same goes for October (eight), November (nine), and December (ten).

Just about the one thing the Romans didn’t give us for our calendar is the AD/BC split. That one came a few centuries later. Before then, years were reckoned from the time of a well-known event or the coronation of a noble figure such as a king or emperor.

Written in the stars

Let’s turn to the scientific aspect of the calendar for now, since that’s where we can get more insight. We’ll get back to the history shortly, I promise.

The year, scientifically speaking, is the time it takes the Earth to orbit the Sun once, while the day is how long it takes our planet to rotate on its axis. These are the only “natural” units of time measurement; weeks and months and hours are all human invention. Both the year and the day can be found by observation: the day is roughly the time between one noon and the next, and the stars (including the Sun) will return to the same position in the night sky after a year. (Technically, this isn’t entirely accurate, but the inaccuracies are far below the calendar’s resolution.)

Clever readers will note that we’ve already run into a big problem: the year is not made of a whole number of days. It’s not 365 days long, nor is it 366. In fact, it’s something like 365.2422 days. So, if our calendar only had 365, we would effectively lose a day about every four years. But if we made every fourth year a day longer, that makes up for the discrepancy. Hence, leap years.

The Julian calendar had one every four years, no matter what. By the time of the Gregorian reform, the difference between 365.2422 and 365.25 had added up, and they had to skip a few days to get things back on track. (How many days depends on when the reform took place.) To stop that from happening again, they also changed the rules to make only certain century years leap years. And that’s why 2000 was special: the next leap year ending in 00 won’t be until 2400.

The sun and the moon

There’s another way to count the days, and it can even work at night. The Western calendar is a solar calendar; it’s based around the sun. But our months are remnants of a connection to a lunar calendar. It’s right there in the name, too.

Other calendars are exclusively lunar in nature. The Islamic calendar is one example. Months start and end based on the phase of the moon, and in many Muslim countries that is a literal statement, even today. But the lunar period isn’t a whole number of days, either, so Islamic months can have either 29 or 30 days. Due to religious circumstances, the Islamic calendar has exactly twelve months, meaning that it will always be short of the solar year. The current year for Muslims is 1437, and the calendar’s epoch (basically, its starting date) was in 622. Simple arithmetic shows that 1394 solar years have passed since then, a difference of 43.

This doesn’t fit with the seasons, but it’s not really meant to. An alternative is to try to combine the lunar and solar cycles into a single calendar. In the West, we have only the remnants of that, in our months, but some other cultures use what’s called a lunisolar calendar. The most familiar example would be the Jewish religious calendar. Here, we still have twelve months, and they’re still based on the cycle of the moon. Normally. But this is a solar calendar, too, and the seasons are important. So, to keep them roughly where they should be, the Jewish calendar adds extra months. It’s like our leap days, but 30 at a time. Seven of these every 19 years keeps things fairly even, plus or minus a month.

From scratch

I’m not going to try to explain the Mayan calendar. It confuses me, so I don’t even know where to begin. Instead, I’ll move on to some thoughts on making a fantasy (or even sci-fi) calendar.

First things first, you need to know the relationship between the year and the day. That’s the key. If you’re working with Earth (or a reasonable facsimile), you already know this, and you can move on. Otherwise, you’re deep in worldbuilding territory, and you’ll probably have to work things out yourself. In that case, remember that it’s going to be pretty rare to have a year with an integral number of days. In fact, it’s almost impossible, and it’s surely temporary. Just about every calendar, with the possible exception of one for an interstellar empire, will have leap days of some sort. They might be scattered throughout the years, or they may come in bunches, but they will be there.

The year and the day mark the cornerstones of the calendar, no matter what kind you have. In between, however, things are wide open. Obviously, lunar-based calendars require at least one moon, and that moon needs to be in an orbit that fits. Phobos, the inner moon of Mars, would be completely useless for a lunar calendar, for example: its orbital period is about 7-1/2 hours. Multiple moons give us the possibility of measuring by conjunctions, but that can get into some heavy math that might be too much for a fantasy world. That’s not to say it’s not worth trying, just that it may not be worth the effort in the end.

Even without a big moon in a nice, useful orbit, cultures would likely develop divisions of time between the day and year. Seasons are appropriate for this, and I’ve got just such a post for that. Weeks are more of an invention of civilization. Our seven-day week dates back to Babylonian times, but many cultures have a shorter period of days than the month. Cyclical religious observances are one excuse for a week, but more mundane concerns, like markets, can also come into play. (A story I’m currently writing has a culture with a week of six days, while the French Revolution tried to institute a ten-day week. About the only place they succeeded was in D&D’s Forgotten Realms setting.)

Now, when the year starts is a question that depends heavily on not just your world but your culture. The Romans liked it in spring, and that has a lot going for it in an agrarian society. The Gregorians moved it to January (to have it closer to Christmas or something like that), but that put it in wintertime. There are arguments for just about any day of the year to be New Year’s, but it’s probably—though not always—going to be at the start of the month, and the date will likely have some cultural, religious, or economic significance.

We can go “below” the day, too, but we begin to run into limitations of technology. Hours are fairly easy, and many early cultures settled on numbers like 12, 24, or 60 of them in a day. Why? For the same reason that there are twelve inches in a foot and twelve (troy) ounces in a pound: it’s easier to divide into halves, fourths, and thirds. (Decimal numbers are great for working on paper, but horrible for eyeballing.) Of course, another planet with a different rotation period will have different hours. On Mars, the obvious “hour” would be about a minute and a half longer than ours.

Measuring minutes and seconds is…harder. It’s likely beyond the reach of many early civilizations, and they likely wouldn’t see the need for it, anyway. We have 60 minutes in an hour or seconds in a minute because, again, 60 is easier to work with until pen and paper are widespread calculating devices. If hours had only been subdivided after the French invented the metric system, we’d probably have 100 of them. (Put the metric system in ancient times, and we would all be using Swatch’s silly Internet Time today, I guess. Anybody remember that thing?)

Last but not least, we come to the reckoning of years. For the West, we count from a monk’s imperfect calculation of the birth of Christ. Muslims go by the rather more specific date of Muhammad’s move to Medina, while Jews start their calendar with the traditional date of the Biblical creation of the world. Other options exist, though. One common one in history is dating by years since a ruler’s rise to the throne; when a new ruler is crowned, a new era begins. Another is a cycle of years called indictions. In this system, the last year of one cycle is followed by the first of a new cycle. We might say that this is the seventh year of the 2010s, for example, or the sixth year of this decade. In a way, the Mesoamerican calendars function something like this. (I’ve actually seen this in fantasy before, too. Scott Lynch, in The Lies of Locke Lamora, has a kind of indiction system. Each year is named after one of the setting’s twelve gods, in a specific order. When the last one is reached, the whole thing loops back to the start.)

Happy New Year

However the calendar works, it gives an otherworldly feel to any fiction. To give you one example, my aforementioned story is set on a different planet. (Well, the first part is mostly set on Earth, but that’s neither here nor there.) That planet has a different day length (24 hours, 23 minutes, approximately) and year length (about 374.16 local days) than our own, meaning that I had to do some work.

What I came up with was a calendar of twelve months, each 30 days long, which doesn’t really have any relation to the orbital period of the planet’s moon; it’s more a matter of convenience. Each month is made of five weeks of six days. The extra days are scattered around the calendar, a few at the end of each season. There are more of them at the end of spring, and fewer at the end of fall, and this has a scientific basis: the eccentricity of the planet’s orbit. Days in this fictional world are 24 hours long, but their hours are slightly longer than our own. Hours can be divided into minutes, and further into seconds, but this is more a math trick than something practical.

You can do things differently, and you probably should. What you make should be tailored for your fictional world, for your story. The key is suspension of disbelief. It doesn’t really make much sense for a world with no connection to Earth at all to be calling their months October and their days Saturday. (I didn’t talk much about the names of the days. They’re pretty obvious, though: planets or gods, not that there’s much difference in older times.) Now, you can say that it’s an author translation of unfamiliar terms, and that’s fine, but taking a little bit of time to work things out can pay off in making your world feel more real.

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