Aztecs used the sun to predict harvest seasons

If you’re an avocado toast or guacamole aficionado, there’s a good chance the delicious green goodness you’re eating was grown in Mexico. In 2019, the United States imported $28 billion worth of agricultural products from Mexico, chief among them fresh fruit and vegetables.

It turns out that Mexico’s agricultural dominance dates back centuries, long before Spanish colonization began in 1519. Prior to the arrival of the Spanish, the agricultural system in the Mexican Basin, a 3,700-square-mile highland plateau in central Mexico, fed a large population. time. Mexico City (called Tenochtitlan) was home to as many as 3 million people, compared to the 50,000 in Seville, Spain’s largest city centre.

A study published today in the journal Proceedings of the National Academy of Sciences (PNAS) It details how the Mexicans or Aztecs were able to obtain such an accurate agricultural calendar.

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An accurate calendar was crucial to growing the food that feeds so many people in a region with a dry spring and summer monsoons. Because planting crops too early or too late can be disastrous, farmers needed advanced knowledge of when these seasonal changes in weather would come. They also needed a calendar that could adapt to a leap year.

Colonial historians have documented the use of a calendar, but this new research shows that Mexico used the Basin mountains as a solar observatory and followed the sunrise against the peaks of the Sierra Nevada mountains.

Exequiel Ezcurra, lead author of the study and a professor of ecology at the University of California, said: “We concluded that they must have stood in one spot, looking east from one day to the next, to tell the time of year by watching the rising sun.” Riverside said in a statement.

To find the point, the team studied Mexican manuscripts, particularly those that mention Mount Tlaloc. There was a temple on the top of the mountain to the east of the basin. Using astronomical computer models, the team confirmed that a long path-like structure in the temple was aligned with the rising sun on February 24. February 23 or 24 is the first day, depending on which calendar (Gregorian or Julian) is used as a comparison. Aztec new year.

“Our hypothesis is that they used the entire Valley of Mexico. Their working instrument was the Basin itself. When the sun rose at a turning point behind the Sierra Mountains, they knew it was time to start planting,” added Ezcurra.

When viewed from a fixed point on Earth, the sun does not follow the same orbit every day. During the winter, the sun runs south of the celestial equator and rises to the southeast. As the longer days of summer approach, sunrise moves northeast due to Earth’s tilt. This process is called solar aberration.

The stone gateway of the solar observatory on Mexico’s Mount Tlaloc aligns with the rising sun on February 23-24, coinciding with the Mexican new year. CREDIT: I’m Meissner.

This study is potentially the first to show how Mexicans can keep time using this principle with the sun and mountains as guiding signs. Learning about these Aztec methods offers a lesson on the importance of using various techniques to solve questions about the natural world.

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“The Aztecs were as good or better at keeping time, using their own way, than the Europeans,” Ezcurra said.

The observatory may also have a modern function today. Historical footage shows the forest slowly climbing Mount Tlaloc, possibly due to an increase in average temperatures at lower altitudes.

“In the 1940s the tree line was well below the peak. Now there are trees growing at the top,” Ezcurra said.

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