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March 31, 2005

Rerun Week: Counting the Days

Be happy for me: The chapter of my book that's been killing me is now complete. It's all steeply downhill from here, and that's good. Here's today's rerun.



The Mayan Calendar. I'm writing this on December 16, 1999 -- on the Mayan calendar, it's That's right, only 5,485 days until the next baktun! Better hit the mall now!

Typically speaking, calendars do two things (beyond, of course, giving "Far Side" cartoonist Gary Larson a way to recycle decade-old cartoons for ready cash). First of all, they provide us with the ability to meaningfully note the passage of time. For example, today is the 226th anniversary of the Boston Tea Party, the 55th anniversary of the Battle of the Bulge and the 78th-month "anniversary" of my first date with my wife (we were obviously not married at the time). One week from today will be my daughter's first birthday. Send gifts.

All these events are contingent on our calendar for their notability relative to the time in which I exist; If we noted weeks and months differently, it might be the anniversary of something else entirely different. Months and weeks have no basis outside us: We made them up, or, if you prefer, God made them up, and we went with his basic plan (don't we always).

The second thing calendars do is notify us of the cyclical nature of our planet. Thanks to a more or less fixed tilt of the earth's axis and a regular period of revolution around our sun, our world gets hot and cold on a predictable schedule, and the patterns of life take note. Flowers bloom in the spring. Animals hibernate in the winter. Leaves fall in autumn. We get re-runs in the summer. It's the circle of life. For various reasons primarily relating to food, the planting and harvesting of, we've needed to know when to expect the seasons to come around again.

The problem has always been that humans have picked bad ways to note that passage of time. The biggest culprit has been the moon. It has a cycle, of course, about 29 days from new moon to new moon. Alas, that cycle has no real relation with the earth's position in its orbit. So while creating months relative to the moon (the word "month" is in fact etymologically descended from the old English word for "moon"), is perfectly fine for recording subjective blocks of time, it's rather less helpful in keeping track of when the seasons are coming. Sooner or later you'd get snow in July. And that would just wreak havoc on your baseball schedules.

Some of your smarter civilizations switched to a calendar in which the year was demarcated by the path of the sun (in the case of the Egyptians, they used Sirius, the Dog Star. Those crafty Egyptians). This was better, as there was, in fact, a direct relation of the sun's path and our year. But the rotation of the earth does not correspond exactly to its revolution. There's an extra quarter of the day (but not exactly a quarter of a day) thrown in for chuckles. Give it enough time, and your seasons and your months will still get away from you.

So you keep fiddling. Our current Gregorian calendar deals with it by inserting a leap day every four years, except in years that end with double zero, except those years which are cleanly divisible by 400. Like 2000. Don't worry, scientists are keeping track of these things for you. Be that as it may, there's still slippage. Calendars aren't an exact science.

Enter the Mayans, who, it should be noted, were the kick-ass mathematical minds of the pre-computational world (they used zeros before zeros were cool!). While everyone else was looking at the sun or the moon as a guidepost for the passage of time, the Mayans looked a little to the left of the sun and discovered...Venus, which as it happens, has an exceptionally predictable path around the sun that takes 584 days. Five of these cycles just happens to coincide with eight 365-day years. Thrown in a couple of additional formulae, and you can keep time that's damn near perfect -- The Mayan calendar loses a day about once every 4000 years. Consider we can't go four years without having to plug in a day, and we've got atomic clocks and everything.

So why don't we switch to a Mayan calendar? Well, this is why:

First bear in mind that the Mayan kept track of two years simultaneously: the Tzolkin, or divinatory calendar, which is comprised of 260 days, demarcated by matching one of 13 numbers with one of 20 names (13x20=260 -- you can do at least that much math), and also another calendar of 18 months of 20 days, with five extra days known as the "Uayeb," for Days of Bad Omen (probably not a good time to do much of anything).

These two calendrical systems linked together once every 18,980 days (that's 52 years to you and me): this period of time was known as a "Calendar Round." Two calendar rounds, incidentally, make up another time period in which the Tzolkin, the 365-day calendar, and the position of Venus sync up again. Think of this as a Mayan century, if you will.

With me so far? Okay, because, actually, I lied. There's another calendar system you need to keep track of as well: The Long Count. Here's how this one works. You start of with a day, which in Mayan is known as a kin. There are 20 kin in a unial, 18 unials in a tun, 20 tun in a katun, and 20 katun in a baktun (so how many days is that? Anyone? Anyone? 144,000 -- roughly 394 years). Each of these is enumerated when you signify a date, with the baktun going first. However, remember that while kin, tun, and katun are numbered from 0 to 19, the unial are numbered from 0 to 17, while the baktun are numbered from 1 to 13. So if someone tries to sell you a Mayan calendar with a 14 in the baktun's place, run! He's a bad man!

And thus, combining our Long Count calendar with our Tzolkin and our 365-day calendar, we find that today is, 6 kan, 12 mak. Now you know why we don't use the Mayan calendar. And the next time you plan to cheat on a math test, sit next to a Mayan.

What happens after you reach the 13th baktun? I don't know, but it's going to happen pretty soon --the Mayan calendar rolls over on December 23rd, 2012. Maybe then we'll get a real apocalypse. Until then, let's all party like it's

Posted by john at March 31, 2005 10:30 AM

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Guy Matthews | March 31, 2005 01:18 PM

Surely since 13 is still permissible we're only looking at the apocalypse on or just after,, some 401 Gregorian years from now.

John Scalzi | March 31, 2005 01:31 PM

Quiet, you.

In any event, the Mayans believed that after the current Baktun (which is the 13th), there would be a great reawareness of time and space, or something along that line, so no matter what, if you're a Mayan, something's coming down the pike in 2012.

What's also interesting is that (apparently, just in case) there are larger time cycles than the baktun. They are:

Piktun (8,000 Years)
Kalabtun (160,000 Years)
Kinchiltun (3,200,000 Years)
Alautun (64,000,000 Years)
Hablatun (1,280,000,000 Years)

So one assumes that what they would actually do is just add another number to their numbering scheme, so the first day past the 13th backtun would be

Brian Greenberg | March 31, 2005 02:42 PM

So when's the big party in the Yucatan Times Square? Is it on, or (which is really the beginning of the next Piktun).

My head hurts...

Anonymous | March 31, 2005 03:07 PM

youre weird

John Scalzi | March 31, 2005 03:19 PM


marrije | March 31, 2005 04:07 PM

"One week from today will be my daughter's first birthday" Awwwww. They grow up so fast, don't they?

ajay | April 1, 2005 10:30 AM

Venus, being closer to the sun, goes round it faster than Earth - so it can't be true that "Venus... has an exceptionally predictable path around the sun that takes 584 days." In fact (quick Google break) a Venerian (Venusian? Venery? Venereal? Venish?) year is 224.7 days. And you a science fiction writer. Robert Heinlein would be ashamed of you.

On the other hand (slightly longer Google break) I see now that you meant 'synodic period' which is the time for one orbit relative to the earth (ie time between two conjunctions). Which is as near as dammit 1.6 years. Exactly as you said.

Well (mutters defensively) I don't think you explained it very well, all the same.

Not to mention the Hindu Calendar of the Four Epochs, which divides History So Far into the Golden Age, Silver Age, New Wave, and Crisis on Infinite Earths (ah hell...) or rather: the Age of Knowledge, the Treta Yug, the Dwapara Yug and the present one, the Age of Kali. (the worst one... naturally. Started around 3000BC; from a Hindu PoV it's been pretty hellish ever since.)
Unnervingly the Kali Yug is the last one in the cycle. It is supposedly brought to an end by Lord Shiva (see 'the radiance of a thousand suns', Oppenheimer, etc) after which the whole cycle starts again.

And the French Revolutionary calendar - which rhymes.

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