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Mesoamerican calendars are the calendrical systems devised and used by the pre-Columbian cultures of Mesoamerica. In addition to the basic function of a calendar—defining and organizing periods of time in a way that allows events to be fixed, ordered and noted relative to each other and some absolute progression—Mesoamerican calendars were also used in religious observances and social rituals, such as for divination.
Among the various calendar systems in use, two were particularly central and widespread across Mesoamerica. Common to all recorded Mesoamerican cultures, and the most important, was the 260-day calendar, a ritual calendar with no confirmed correlation to astronomical or agricultural cycles. Apparently the earliest Mesoamerican calendar to be developed, it was known by a variety of local terms, and its named components and the glyphs used to depict them were similarly culture-specific. However, it is clear that this calendar functioned in essentially the same way across cultures, and down through the chronological periods it was maintained. The second of the major calendars was one representing a 365-day period approximating the tropical year, known sometimes as the "vague year". Because it was an approximation, over time the seasons and the true tropical year gradually "wandered" with respect to this calendar, owing to the accumulation of the differences in length. There is little hard evidence to suggest that the ancient Mesoamericans used any intercalary days to bring their calendar back into alignment. However there is evidence to show Mesoamericans were aware of this gradual shifting, which they accounted for in other ways without amending the calendar itself.
These two 260- and 365-day calendars could also be synchronised to generate the Calendar Round, a period of 18980 days or approximately 52 years. The completion and observance of this Calendar Round sequence was of ritual significance to a number of Mesoamerican cultures.
A third major calendar form known as the Long Count is found in the inscriptions of several Mesoamerican cultures, most famously those of the Maya civilization who developed it to its fullest extent during the Classic period (ca. 200–900 CE). The Long Count provided the ability to uniquely identify days over a much longer period of time, by combining a sequence of day-counts or cycles of increasing length, calculated or set from a particular date in the mythical past. Most commonly, five such higher-order cycles in a modified vigesimal (base-20) count were used, generating a linear progression of days to span a period of roughly 5125 solar years.
The use of Mesoamerican calendrics is one of the cultural traits that Paul Kirchoff used in his original formulation to define Mesoamerica as a culture area. Therefore the use of Mesoamerican calendars is specific to Mesoamerica and is not found outside its boundaries.
The existence of Mesoamerican calendars is attested as early as ca. 500 BCE, with the essentials already appearing by then as fully defined and functional. Mesoamerican calendar usage—of one form or another, some (such as the Long Count) fell into disuse earlier—continued throughout the pre-Columbian era until the arrival of the Spanish conquistadores in the early 16th century. Even after the subsequent colonialisation of Mesoamerican territory by Europeans and the consequent adoption of the Julian Calendar, some indigenous communities continue to use aspects of Mesoamerican calendars in parallel with the Western system, such as among K'iche Maya communities of the Guatemalan highlands and the Mixe of Oaxaca.
Ritual 260-day calendar 
In the 260-day cycle 20 day names pairs with 13 day numbers, totalling a cycle of 260 days. This cycle was used for divination purposes, it foretold lucky and unlucky days. The date of birth was also used to give names to both humans and gods in many Mesoamerican cultures, some cultures used only the calendar name whereas others combined it with a given name. Each day sign was presided over by a god and many had associations with specific natural phenomena.
The exact origin of the 260-day count is not known, but there are several theories. One theory is that the calendar came from mathematical operations based on the numbers thirteen and twenty, which were important numbers to the Maya. The numbers multiplied together equal 260.
Another theory is that the 260-day period came from the length of human pregnancy. This is close to the average number of days between the first missed menstrual period and birth, unlike Naegele's rule which is 40 weeks (280 days) between the last menstrual period and birth. It is postulated that midwives originally developed the calendar to predict babies' expected birth dates.
A third theory comes from understanding of astronomy, geography and paleontology. The mesoamerican calendar probably originated with the Olmecs, and a settlement existed at Izapa, in southeast Chiapas Mexico, before 1200 BCE. There, at a latitude of about 15° N, the Sun passes through zenith twice a year, and there are 260 days between zenithal passages, and gnomons (used generally for observing the path of the Sun and in particular zenithal passages), were found at this and other sites. The sacred almanac may well have been set in motion on August 13, 1359 BCE, in Izapa.
The 260-day period was divided into periods of 13 days called in Spanish a trecena (no indigenous word for this period is known). The days of a trecena were usually numbered from 1 to 13. There were some exceptions, such as in the Tlapanec area where they were counted from 2 to 14. The first day of the trecena, and the god who was its patron, ruled the following thirteen days. If the first day of a trecena was auspicious then so were the next twelve days.
Solar 365-day calendar 
This 365-day calendar was corresponded roughly with the true solar year, was divided into 18 'months' of 20 days each, plus 5 'nameless' days at the end of the year. It seems however that the mesoamericans did not take the leap year into consideration, meaning that the year was pushed a quarter of a day from the true solar year, each year.
The years were given their name in much the same way as the days of the 260-day calendar, 20 names were paired with 13 numbers giving 52 different possibilities for year names
The solar year was divided into 18 'months' of each 20 day called veintenas in Spanish and meztli in nahuatl, meaning moon. The order of the months was always the same, but it is still debated which month started the Mexican year. Each month had its own specific ceremonies that were conducted in the end of the 20-day period.
The five unlucky days 
The five unlucky days were called nemontemi in Mexico. Most believe them to have come at the end of each year, but since we do not know when the year started, we cannot know for sure. We do know though, that in the Maya-area these five days (called Wayeb in Maya) were always the very last days of the year. The nemontemi were seen as 'the useless days' or the days that were dedicated to no gods, and they had prognostic power for the coming year. Therefore People tried to do as little as possible on these days, and a person who was born during the nemontemi was considered unlucky.
Calendar Round 
Since both the Tonalpohualli- and the Xihuitl calendar constantly repeat themselves, approximately every 52 years they reach a common end, and a new Calendar Round begins. This 52-year cycle was the most important for most Mesoamericans, with the apparent exception of the Maya elite until the end of the Classic Era, who gave equal importance to the Mesoamerican Long Count calendar. According to their mythology, at the end of one of these 52-year cycles the world would be destroyed by the gods, like it had happened four times previously. While waiting for this to happen, all fire was extinguished, house utensils were destroyed in the houses to symbolize new beginnings, people fasted and rituals were carried out. This was known as the New Fire Ceremony. When dawn broke the first day of the new cycle, torches were lit in the temples and brought out to light new fires everywhere, and ceremonies of thanksgiving were performed.
Religion and calendrics 
Lords of the day 
There were 13 Lords of the Day. These were gods (and goddesses) who each represented one of the 13 days in the trecenas of the 260-day calendar. The same god always represented the same day. Quetzalcohuatl (The feathered serpent), for example, always accompanied the 9th day.
Lords of the night 
There are only nine Lords of the Night, which means that they cannot always represent the same day, but the list of gods repeats itself again and again so each lord accompanies a new number each trecena. Some think that there are nine Lords of the night because they are connected to the nine levels of the underworld.
Long Count 
The 365-day and the 260-day calendars identified and named the days, but not the years. The combination of a solar year date and a 260-year date was enough to identify a specific date to most people's satisfaction, as such a combination did not occur again for another 52 years, above general life expectancy. To measure dates over periods longer than 52 years, the Mesoamericans devised the Long Count calendar. This calendar system was probably developed by the Olmecs and later adopted by the Maya. The use of the long count is best attested among the classic Maya, it is not known to have been used by the central Mexican cultures.
The Long Count calendar identifies a date by counting the number of days from August 11, 3114 BCE in the proleptic Gregorian calendar or September 6 3114 BCE in the Julian Calendar (-3113 astronomical). Rather than using a base-10 scheme, like Western numbering, the Long Count days were tallied in a modified base-20 scheme. Thus 0.0.0.1.5 is equal to 25, and 0.0.0.2.0 is equal to 40.
52 year cycle 
The correlation of the 52 year day count cycle to the European calendar is problematic, mostly because the calendar usage wasn't synchronized between all of the communities of Mesoamerica. This means that one must know its origin and the specific correlation applicable for that place. Secondly it is made difficult by the possibility that the cycle might at times be "reset" for political purposes - for example if a ruler wanted to mark his rule as the beginning of a new dynasty.[verification needed]
Often the best correlation can be made when both European and indigenous sources give a specific date. For example, we know from Spanish sources that the day the Aztec capital Tenochtitlan fell was on August 13, 1521. Indigenous sources from central Mexico agree that this was the day Ce Cohuatl (1 Snake) in the year Eyi Calli (3 house).
For a number of reasons however, it is difficult to correlate to the preciseness of a day. Mainly because it is suspected that the Mesoamericans counted their days as starting at noon, for the obvious reason that the zenith of the sun is more easily observed than, for example, the exact time of midnight. Thus there will always be at least the bias of half a day in the correlations. There is also the problem of the transition in Europe from the Julian to the Gregorian calendar, which happened during the time when many of the sources were written. This can create confusion as to which calendar, and thereby which exact day is referred.
Long count 
There have been various methods proposed to allow us to convert from a Long Count date to a Western calendar date. These methods, or correlations, are generally based on dates from the Spanish conquest, where both Long Count and Western dates are known with some accuracy.
The commonly-established way of expressing the correlation between the Maya calendar and the Gregorian or Julian calendars is to provide number of days from the start of the Julian Period (Monday, January 1, 4713 BCE) to the start of creation on 0.0.0.0.0 (was actually 184.108.40.206.0) 4 Ajaw, 8 Kumk'u.
The most commonly accepted correlation is the "Goodman, Martinez, Thompson" correlation (GMT correlation). The GMT correlation establishes that the creation date occurred on 3114 BCE September 6 (Julian) or 3114 BCE August 11 (Gregorian), Julian day number (JDN) 584283. This correlation fits the astronomical, ethnographic, carbon dating, and historical sources. However, there have been other correlations that have been proposed at various times, most of which are merely of historical interest, except that by Floyd Lounsbury, two days after the GMT correlation, which is in use by some Maya scholars, such as Linda Schele.
Maya Calendar 
The Maya version of the 260-day calendar is commonly known to scholars as the Tzolkin, or Tzolk'in in the revised orthography of the Academia de Lenguas Mayas de Guatemala. The Tzolk'in is combined with the 365-day calendar (known as the Haab, or Haab' ), to form a synchronized cycle lasting for 52 Haabs, called the Calendar Round. Smaller cycles of 13 days (the trecena) and 20 days (the veintena) were important components of the Tzolk'in and Haab' cycles, respectively. The Maya called the 5 unlucky days at the end of the solar year for Wayeb'.
The Classic Maya, but not the post-classic highland Maya, also used the Long count to record dates within periods longer than the 52 year calendar round. Many Maya Long Count inscriptions are supplemented by what is known as the Lunar Series, another calendar form which provides information on the lunar phase and position of the Moon in a half-yearly cycle of lunations.
A 584-day Venus cycle was also maintained, which tracked the appearance and conjunctions of Venus as the morning and evening stars. Many events in this cycle were seen as being inauspicious and baleful, and occasionally warfare was timed to coincide with stages in this cycle.
Other, less-prevalent or poorly-understood cycles, combinations and calendar progressions were also tracked. An 819-day count is attested in a few inscriptions; repeating sets of 9- and 13-day intervals associated with different groups of deities, animals and other significant concepts are also known.
Central Mexican Calendar 
The Central Mexican calendar system is best known in the form that was used by the Aztecs, but similar calendars were used by the Mixtecs, Zapotecs, Tlapanecs, Otomi, Matlatzinca, Totonac, Huastecs, P'urhépecha and at Teotihuacan. These calendars differed from the Maya version mainly in that they didn't use the long count to fix dates into a larger chronological frame than the 52-year cycle.
The Aztecs referred to the 365 and 260-day cycles as xiuhpohualli (year count) and tonalpohualli (day count) respectively. The Veintena was called metztli (moon), and the five unlucky days at the end of the solar year were called nemontemi.
Other cycles 
Comparison between veintena and trecena names in different cultures 
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See also 
- Marcus (1992)
- Miller and Taube (1993, p.48)
- Miller and Taube (1993, p.50)
- Miller and Taube (1993, pp.50–51)
- "Mesoamerica: Our Region". Mesoamerica. Retrieved 2006-12-19. "Paul Kirchhoff coined the term, Mesoamerica in 1943 from the Greek mesos or "center" and America."
- Caso (1971, p.333)
- See Coe (1987, p.47); Miller and Taube (1993, p.48).
- Caso (1971, p.333), Edmonson (1988, p.5)
- Hanns J. Prem, Antigua cronología Mexicana (p. 70)
- Handbook of middleamerican indians, book 10 (pp. 339-340)
- Broda de Casas, The Mexican Calendar (pp. 18-19)
- Miller and Taube (1992, pp.86–88)
- Broda de Casas, The Mexican Calendar (pp. 27-28)
- Handbook of middleamerican indians, book 10 (pp. 335-336)
- Refer ALMG (1988), as cited in Kettunen and Hemke (2005, p.5). This latter notes the general adoption on ALMG orthography among the Mayanist research community.
- Balkansky (2002); Miller and Taube (1992, pp.52–54)
- ALMG (Academia de Lenguas Mayas de Guatemala) (1988). Lenguas mayas de Guatemala: documento de referencia para la pronunciación de los nuevos alfabetos oficiales. ALMG Documento 1. Guatemala City: Instituto Indigenista Nacional, Ministerio de Cultura y Deportes. OCLC 20330408. (Spanish)
- Balkansky, Andrew (2002). "Zapotec Hieroglyphic Writing, by Javier Urcid Serrano [Book Review]". Antiquity (Cambridge, England: Antiquity Publications) 76 (293): 904–905. ISSN 0003-598X. OCLC 1481624. Retrieved 2006-10-20.
- Caso, Alfonso (1971). "Calendrical Systems of Central Mexico". In Gordon F. Ekholm and Ignacio Bernal (Volume eds.). Handbook of Middle American Indians, Vol. 10: Archaeology of Northern Mesoamerica, part I. R. Wauchope (General Editor). Austin: University of Texas Press. pp. 333–348. ISBN 0-292-70150-0. OCLC 277126.
- Coe, Michael D. (1987). The Maya. Ancient peoples and places series (4th edition (revised) ed.). London and New York: Thames & Hudson. ISBN 0-500-27455-X. OCLC 15895415.
- Edmonson, Munro S. (1988). The Book of the Year: Middle American Calendrical Systems. Salt Lake City: University of Utah Press. ISBN 0-87480-288-1. OCLC 17650412.
- Hassig, Ross (2001). Time, History, and Belief in Aztec and Colonial Mexico. Austin: University of Texas Press. ISBN 0-292-73139-6. OCLC 44167649.
- Kettunen, Harri; and Christophe Helmke (2005). Introduction to Maya Hieroglyphs (PDF online publication). Wayeb and Leiden University. Retrieved 2008-08-07.
- Marcus, Joyce (1992). Mesoamerican Writing Systems: Propaganda, Myth, and History in Four Ancient Civilizations. Princeton, NJ: Princeton University Press. ISBN 0-691-09474-8. OCLC 25549355.
- Malmström, Vincent H. (September 17, 1973). "Origin of the Mesoamerican 260-Day Calendar" (PDF Reprinted). Science (Lancaster, PA: American Association for the Advancement of Science) 181 (4103): 939–941. Bibcode:1973Sci...181..939M. doi:10.1126/science.181.4103.939. PMID 17835843.
- Malmström, Vincent H. (1997). Cycles of the Sun, Mysteries of the Moon: The Calendar in Mesoamerican Civilization (online reproduction by author ed.). Austin: University of Texas Press. ISBN 0-292-75197-4. OCLC 34354774. Retrieved 2007-11-26.
- Miller, Mary; and Karl Taube (1993). The Gods and Symbols of Ancient Mexico and the Maya: An Illustrated Dictionary of Mesoamerican Religion. London: Thames & Hudson. ISBN 0-500-05068-6. OCLC 27667317.
- Nowotny, Karl Anton (2005). Tlacuilolli: style and contents of the Mexican pictorial manuscripts with a catalog of the Borgia Group. George A. Everett, Jr. and Edward B. Sisson (trans. and eds.), with a foreword by Ferdinand Anders. Norman: University of Oklahoma Press. ISBN 0-8061-3653-7. OCLC 56527102.
- Note on the Maya Calendar, Michael Finley (2002)
- Mesoamerican Archaeoastronomy and calendars, James Q. Jacobs (1999)
- PDF (1.5 MB), article at Convergence online magazine, published by the Mathematical Association of America