The term Mesoamerica refers to the region between south central-Mexico and Nicaragua. It was a multi-ethnic, multi-lingual area that shared a number of cultural characteristics: a 260-day ritual calendar, a 52-year cycle, monumental pyramid structure, a ceremonial ball game, ritual heart sacrifice, and a diet consisting of maize, beans and squash.
It is generally accepted that the first known civilisation in the Americas is that of the Olmec (c.1500-c.400 BC) which expanded from the coasts of Veracruz and west Tabasco on the Gulf of Mexico, and whose culture passed in varying degrees to subsequent Mesoamerican groups.
Originating in the Yucatan around 2600 BC the civilisation of the Maya (c. 250-c.900) at its peak extended through Chiapas, Tabasco, the Yucatan Peninsula, Guatemala, Belize, El Salvador and western Honduras. Building on the ideas of earlier civilisations such as the Olmec, the Maya developed astronomy, calendrical systems, and hieroglyphic writing.
They used a long count that reckoned the number of days that had lapsed since the most recent cycle of creation and corresponds in the Christian calendar to a date of 11 (or 13) August 3114 BC. A short count of 260-days predated the long count by several centuries. The paths of the Sun and Moon cross every 173.31 days, and a solar eclipse can only occur within a few days of this event. Three of these 173.31-day intervals almost exactly equal two Maya 260-day counts, a cycle that they could use for reckoning eclipses.
In the first century AD, inscriptions refer to a second short cycle, the 365-day year or haab of eighteen months of twenty days plus five extra days. Comparing the two cycles, a given date does not repeat in both until 73×260 or 52×365 days (the 52-year cycle) have elapsed. We call this the calendar round.
Mayan astronomy tables incorporate numbers, words and pictures. Events are positioned in time, and methods are given for predicting future events. The Dresden Codex (13th or 14th century) gives a table for predicting solar and lunar eclipses, an ephemeris for Mars and another for Venus. Because the ratio between the haab (365 days) and the synodic period of Venus (584 days) is 5:8, the Maya could predict that when the planet made a heliacal rise it would do so again almost exactly on the same day eight solar years later.
The haab (the 365-day Mayan year) makes no allowance for leap years, but the Maya also tracked the solar year. In the tropics, the Sun stands directly overhead at noon twice each year. In the Yucatan, these zenith passages occur in May and July, and mark the times when crops are planted. Determining the zenith passage of the Sun is a simple matter: sunlight will reach the bottom of a narrow tube when the Sun is directly overhead. At Monte Alban in Oaxaca and in southern Mexico, zenith tubes appear to have been built into artificial caves beneath monuments.
Given their obsession with mathematics and astronomy it would not be unreasonable to expect that their buildings incorporated astronomy alignments. However, because each of the different complex structures is unique in form, it is difficult in any given instance to prove that the alignment is intentional rather than accidental.
The possibility of Mesoamerican observational technology is present in pictographs that appear to indicate men peering over two crossed sticks. This could have been used as a sighting device to establish periodicities by observing when a celestial object resumed its earlier position in a window or doorway. Chichen Itza, a Maya centre in north Yucatan, includes a cylindrical edifice El Caracol (Spanish: ‘snail’), a name that refers to the building’s spiral stairway. El Carocal may have been an observatory. Alignments appear to match the equinox sunset and the lunar and the planet Venus extremes.
During the first century AD the city-state Teotihuacan appeared in central Mexico. At its peak (c.450-c.650) it was the most populous city in the Americas. Archaeological evidence suggests that the construction of this city was carefully planned. At the heart of the city is a complex of major structures including the huge pyramids of the Sun and Moon.
The Pyramid of the Sun was aligned to coincide with the two days (19 May and 25 July) when the Sun was directly over the top of the pyramid at noon. Also on these two dates the west face of the pyramid was oriented precisely to the position of the setting Sun. In South America the Inca Civilisation (1438-1532) began as the small city-state of Cuzco and then starting under the command of Pachacuti (r.1438-1471) they conquered much of modern-day southern Peru. Radiating out from Cuzco are forty-two ceques (=lines) that seem to represent political boundaries and pathways dotted with hundreds of small shrines. Several of the orientations of the lines appear to mark relevant astronomy phenomena at the horizon, such as the rising of the Sun at the solstices.
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