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Friday, April 26, 2013

Calibrating the Maya Long Count calendar

Thanks to the media sensation of 2012, we’ve all heard of the Maya Long Count (MLC) calendar. Needless to say, that calendar did not augur the end of the world any more than our calendars do every December 31st. The more interesting question is how well we can correlate events noted on the Maya calendar with dates on our own calendar. Thanks to work led by Douglas Kennett of Pennsylvania State University, we can now be pretty sure we have correctly matched up the two counting methods.

Let’s begin by explaining the MLC calendar. Just as we divide our time periods into sections (millennia, years, days, etc), so too did the Maya. Only, their system included five time units: Bak'tun (144,000 days), K'atun (7,200 days), Tun (360 days), Winal (20 days), and K'in (1 day). In our system, we might designate a date as 4/26/2013 (or 26/4/2013 for you Europeans) to show that it’s the twenty-sixth day of the fourth month in the two thousand thirteenth year, or about 735,360 days (if I put in the right number of leap years) since the starting point at 0/0/0. The Maya would have designated that same time span as (5 Bak’tuns, 2 K’atuns, 2 Tuns, 12 Winals and 0 K’ins). Of course they didn’t use our numeric system, so it would have looked like a series of bars and dots.

Caption: Elaborately carved wooden lintel or ceiling from a temple in the ancient Maya city of Tikal, Guatemala, that carries a carving and dedication date in the Maya calendar.
Credit: Courtesy of the Museum der Kulturen.

Okay, so we know how to translate the MLC calendar to tell us how many days have passed since they began that count. Unfortunately, that information alone doesn’t yield any insight into the equivalent date on our calendar, because they didn’t start their calendar at the same time as we started ours. Knowing that an event occurred 80,000 days into the MLC doesn’t tell you much if you don’t know when their day zero was. You need to know what correction factor to add to the Maya count to bring it into alignment with the European calendar.

There are two ways to find that correction factor. One is to find an event that was recorded in both calendars. The most commonly used correction, known as the Goodman-Martinez-Thompson (GMT) correlation, is largely based on this sort of historical evidence. The second method is to physically date artifacts that are from a specific Maya date. Kennett and his colleagues followed this tactic.

The researchers took four samples from a wooden lintel in an ancient Maya temple (shown above) that included a date commemorating the defeat of one Maya king by his rival. The researchers used radiocarbon dating of the wooden lintel in conjunction with growth rate estimates for the tree from whence it had come to calculate the actual age of the lintel. From that, they figured out when the regicide had occurred.

Among the various correlations, the GMT, placing the event depicted on the lintel during our year C.E. 695, proved to be most accurate. Other methods of correlating Maya and European dates varied by as much as a five hundred years either way. 

With this new information, we can now accurately match events that occurred on the MLC to dates that we can understand. Luckily, we all lived through 2012 to appreciate this.

Kennett, D., Hajdas, I., Culleton, B., Belmecheri, S., Martin, S., Neff, H., Awe, J., Graham, H., Freeman, K., Newsom, L., Lentz, D., Anselmetti, F., Robinson, M., Marwan, N., Southon, J., Hodell, D., & Haug, G. (2013). Correlating the Ancient Maya and Modern European Calendars with High-Precision AMS 14C Dating Scientific Reports, 3 DOI: 10.1038/srep01597.