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Astronomical Alignments at Teotihuacan, Mexico

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It is known that the grid pattern characterizing the city layout of Teotihuacan incorporates two slightly different groups of alignments, skewed approximately 15.5% and 16.5% clockwise from cardinal directions. I argue that these alignments were dictated by deliberate and astronomically functional orientations of the Pyramid of the Sun and the Ciudadela. The two structures recorded sunrises and sunsets on two different sets of dates, allowing the use of an observational calendar composed of intervals that included multiples of 20 days and a 260-day period. The evidence presented suggests also that the location of the Sun Pyramid was not determined by the cave that is now underneath the structure and is probably human-made, but rather by a combination of astronomical and topographic criteria: the place allowed the temple built there to be oriented both to sunrises and sunsets on significant dates and, in the perpendicular direction, to Cerro Gordo to the north; furthermore, sunrises on the so-called quarter-days of the year could be observed from the same spot over a prominent mountain on the eastern horizon. The dates corresponding to the Teotihuacan alignments are attested also at other central Mexican archaeological sites and must have been employed, primarily, for scheduling agricultural and associated ritual activities in the yearly cycle.
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... The selection of structures to be measured was based on the assumption that the orientational rules reflecting astronomical concepts and related aspects of worldview and religion were more strictly adhered to in civic and ceremonial architecture. If two or more buildings composing an architectural group were found to share a particular orientation, only that of the most prominent structure was considered in the analyses, assuming that those of the adjacent buildings roughly reproduced it but were not observationally functional per se (the most eloquent example is the urban grid of Teotihuacan;Š prajc 2000b. ...
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... Examining building orientations at Teotihuacan, Ivan Sprajc postulated that these alignments and their relation to the annual path of the sun could have been employed to observe calendric cycles, including the definition of an interval that lasted 260 days (Sprajc 2000). He noted that it was at Teotihuacan that two slightly different orientations first appeared together, which made possible an observational calendar (Sprajc 2015(Sprajc , 2018. ...
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