Wednesday, 8 May 2013

The Mesoamerican Calendar

Mesoamerican calendrical systems have become well-known to the general public in recent years as a result of the Maya Long Count, which ended on 21 December 2012. There is no reason to suppose that the Maya expected anything untoward to occur on that day, but that did not stop the doomsday industry from working overtime. As the supposed day of reckoning approached, groups camped out by a mountain in the south of France to await rescue by flying saucer. There was much nonsense about a rogue planet called Nibiru and other supposed perils. The cinema industry cashed in on the hoo-hah with the disaster movie 2012 and the rather more thoughtful Melancholia. Neither movie paid much heed to the laws of physics. In fact, periodic end of the world ‘scares’ are nothing new, and go back at least a thousand years (Moore, 1999).

The Long Count was actually only one of three calendars in use in pre-Columbian Mesoamerica. For day-to-day reckoning, there was a solar calendar or haab cycle of 365 days, and there was a ritual calendar of 260-days known as the tzolkin or sacred almanac. All three calendars made use of the vigesimal or base-20 system of counting, rather than our familiar decimal or base-10 system. The system employed a place-value notation and a zero, long before the Hindu-Arabic system introduced these concepts. It may have come about through the practice of counting the digits on the feet as well as on the hands. Numbers were represented by combinations of ones (dots), fives (bars) and zeros (various characters) stacked vertically, with place value increasing from bottom to top (Aventi, 2001). The other number that featured prominently in Mesoamerican calendrical systems was 13, representing the number of levels of heaven in Mesoamerican cosmology (cf. the seven levels of heaven in the Jewish, Islamic and Hindu traditions).

The haab cycle comprised 18 ‘months’ of 20 days each, plus 5 intercalary days. Each date denoted by one of 20 day names paired with one of 18 month names. Like the pre-Ptolemaic Egyptian calendar, it did not take leap years into consideration, and thus did not accurately track the solar year. Days in the tzolkin were denoted by a number from 1 to 13 and one of 20 names, for a total of 260 days. The haab and tzolkin cycles were combined into the Calendar Round, which repeats every 18980 days (52 years). The 52-year cycle was a period of great significance throughout Mesoamerica. The termination was celebrated by the New Fire ceremony, in which fires everywhere were extinguished and domestic implements and statues were discarded (Aventi, 2001).

The Long Count calendar generated dates from a fixed start point that were to all intents and purposes unique (as are Gregorian dates). The basic unit of time was the tun of 360 days, which was subdivided into 18 uinals of 20 kins (days) each. The tun was multiplied by successive powers of 20 (the vigesimal equivalent of decades and centuries) named katuns and baktuns. Thus a katun is 360 x 20 = 7200 days and a baktun is 360 x 20 x 20 = 144,000 days or just over 394 years. The Maya did not invent the Long Count, but by Classic times (AD 250 – 800), only they were using it (Webster & Evans, 2005). The Maya implementation of the Long Count began on a date corresponding to 11 August 3114 BC in the Gregorian calendar. The 13th baktun from that date ended on 21 December 2012. There is some dispute as to what is supposed to follow. The usual view is that 13 baktuns (just over 5125 years) represents a creation epoch and the count returns to zero (Aventi, 2001). However, there is some evidence that the Maya intended the count to continue. There may be higher-order units beyond the baktun which scholars (in the absence of the original Maya terms) have named the piktun, kalabtun, kinchiltun and alautun.

The reason for a 260-day ritual count remains uncertain. One suggestion is that it originated at a location between 14°42' and 15 N., where the Sun crosses the zenith at 260 and 105-day intervals. A possible candidate is the Late Formative Period site of Izapa, which is located on the Pacific Coast of Mexico (Malmstrom, 1973). One objection to this interpretation is that the 260-day cycle simply repeats and does not factor in the concomitant 105-day cycle (Henderson, 1973). Another problem is that the 260-day cycle may have been in use at Monte Alb├ín around 500 BC, considerably earlier than Izapa (Henderson, 1973; Marcus & Flannery, 2004). There are also Olmec inscriptions that suggest that the cycle might date to as early as 650 BC (Pohl, Pope, & von Nagy, 2002; Stokstad, 2002).

Other suggestions are a link to the average human gestation period of 266 days, or to various astronomical cycles. Two tzolkin (520 days) corresponds closely to three eclipse half-years (519.93 days). The eclipse half-year of 173.31 days is the period between successive eclipse seasons, i.e. a period of around 33 days when the Earth, Moon and Sun can line up to produce an eclipse. There is also a close correspondence between the tzolkin and the average of 263 days that Venus remains visible as either a morning or evening star, before it disappears into the dawn or twilight skies. Links to Mars have also been suggested. The synodic period of the Red Planet (i.e. the interval between successive close approaches to Earth) is almost exactly three tzolkin, or 780 days (Aventi, 2001).

Aventi, A. (2001). Skywatchers. Austin, TX: University of Texas Press.
Henderson, J. (1973). Origin of the 260-Day Cycle in Mesoamerica. Science, 185, 542.
Malmstrom, V. (1973). Origin of the Mesoamerican 260-Day Calendar. Science, 181, 939-940.
Marcus, J., & Flannery, K. (2004). The coevolution of ritual and society: New 14C dates from ancient Mexico. PNAS, 101(52), 18257–18261.
Moore, P. (1999). Countdown!... or how nigh is the end? London: Pan.
Pohl, M., Pope, K., & von Nagy, C. (2002). Olmec Origins of Mesoamerican Writing. Science, 298, 1984-1987.
Stokstad, E. (2002). Oldest New World Writing Suggests Olmec Innovation. Science, 298, 1873-1874.
Webster, D., & Evans, S. (2005). Mesoamerican civilization. In C. Scarre, The human past (pp. 594-639). London: Thames & Hudson.