Arguably the most enigmatic of the Maya calendar cycles, the 819-day count has challenged modern scholars for decades. Even today it is not completely explained and there are several areas for further research, including its relationship with the synodic periods of the planets visible to the naked eye. Earlier research demonstrated a four-part, color-directional scheme for the 819-day count such that each of the calendar stations progress in increments of 819 days in cycles of 4 x 819 days. By increasing the calendar length to 20 periods of 819-days, a duo of U.S. anthropologists discovered a pattern in which the synodic periods of all the visible planets commensurate with station points in the larger 819-day calendar.
The Monolith of the Stone of the Sun, also known as the Aztec calendar stone, in the National Museum of Anthropology and History, Mexico City, Mexico. Image credit: El Comandante / CC BY-SA 3.0.
Scholars long suspected the ancient Maya 819-day calendar followed astronomical events, specifically how long it takes a planet to appear in the same place in the night sky as seen from Earth, known as the synodic periods of planets.
But according to the new study, the cycles in the calendar cover a much larger timeframe than scholars previously thought.
“Although prior research has sought to show planetary connections for the 819-day count, its four-part, color-directional scheme is too short to fit well with the synodic periods of the visible planets,” said Tulane University alumnus John Linden and Professor Victoria Bricker.
“By increasing the calendar length to 20 periods of 819-days, a pattern emerges in which the synodic periods of all the visible planets commensurate with station points in the larger 819-day calendar.”
Previously, scholars thought the calendar referred to four cycles of 819, but that time span didn’t sync neatly with the synodic periods of all the planets that can be seen with the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn.
Linden and Professor Bricker discovered it takes 20 cycles of 819 days, which is about 45 years, to align with the synodic periods of all visible planets.
Within 20 cycles, each planet goes through some number of synodic periods a whole number of times: Mercury every cycle, Venus every 5 cycles, Saturn every 6 cycles, Jupiter every 19 cycles, and Mars every 20 cycles.
Each synodic period is less than 819 days, but only Mercury has one that happens a whole number of times within a single cycle.
Combining the cycles allows for prediction of the placement of the planets, which is also connected to important dates and celebrations.
“Rather than limit their focus to any one planet, the Maya astronomers who created the 819-day count envisioned it as a larger calendar system that could be used for predictions of all the visible planet’s synodic periods,” the scientists said.
“Our research is a key part of understanding how the ancient Maya studied astronomy and is part of a decades-long quest to understand the complexity of ancient Maya calendars.”
The team’s paper was published in the journal Ancient Mesoamerica.
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John H. Linden & Victoria R. Bricker. The Maya 819-Day Count and Planetary Astronomy. Ancient Mesoamerica, published online April 18, 2023; doi: 10.1017/S0956536122000323
