In the year 731, the platform at Copán remains chilly and unyielding against bare feet, while the jungle vibrates with hidden activity. A priest occupies the same spot where his mentor once stood, witnessing the sun rise at the identical point on the horizon as it did a year earlier. This is not a mere coincidence. He is part of a continuous lineage of priests and scribes who, through generations of detailed observations, have determined the length of the solar year with remarkable accuracy.
The duration set by the Maya for the solar year is often cited as 365.2420 days. In comparison, contemporary astronomers have measured the mean tropical year to be 365.24219 days, resulting in a discrepancy of just seventeen seconds. Interestingly, when Pope Gregory XIII instituted the Gregorian calendar in 1582, it was based on a solar year of 365.2425 days, diverging further from the modern calculation.
The Origin of the Maya Solar Year
No Maya inscription explicitly declares the precise length of the solar year. Instead, the figure is inferred from the arithmetic carved on their monuments, thoroughly analyzed by John Teeple, a chemical engineer. Teeple’s comprehensive investigation of Maya stelae throughout Honduras, Guatemala, and Mexico culminated in “Maya Astronomy,” a work that continues to be significant in Mayanist research.
Teeple discovered that the scribes of Copán documented the gradual shift of seasons through their 365-day civil year, the haab, which did not incorporate a leap day. This drift, accounting for one day every four years, was carefully monitored, with Stela A at Copán recording a change of 930 days over 3,844 years since the legendary zero date of the Maya. Teeple concluded that the Maya calculations were more accurate than those employed in the Julian calendar, closely resembling the Gregorian system.
The Maya also exhibited precision in their lunar calendar. At Copán, 149 lunar months were regarded as equivalent to 4,400 days, resulting in an average month length of 29.53020 days. In contrast, the city of Palenque employed a slightly different calculation, achieving 29.53086 days per month. The true lunar month measures 29.53059 days, indicating that both locations attained remarkable accuracy, although they reportedly disagreed on the discrepancy.
Method of Solar Measurement
Reaching this degree of accuracy without modern instruments required generations to observe the same sunrise from specific positions and diligently document its hour on the horizon. Archaeologist Ivan Šprajc assessed the orientations of 71 E Groups and 79 other structures throughout the Maya lowlands. These were aligned with sunrises or sunsets on particular dates of importance in the ritual calendar, constructed from multiples of 13 and 20-day intervals.
Šprajc challenged the common belief that these structures served as equinox observatories, contending that equinoxes are a concept not observable on the horizon—a discussion rooted in extensive measured alignments.
Durability of the Eclipse Tables
An extraordinary instance of Maya precision is the eclipse table located in the Dresden Codex, characterized by John Justeson as “an accurate predictive model” in Sky & Telescope. He and Justin Lowry reaffirmed its precision in Science Advances, demonstrating how these tables successfully forecasted eclipses by resetting at specific cycles, the saros and inex, thus preserving their accuracy for over 700 years.
Permanent Error in the Maya Calendar
Even though they recognized their 365-day year was slightly insufficient, Maya astronomers never modified the haab. Their calendar permitted seasons to shift while arithmetic tracked its advancement. Similar precision is apparent in Venus cycle calculations referenced in the codex, where the total of intervals closely aligns with Venus’s cycle, ensuring synchronization across cycles.
The Maya calendar system, unlike modern calendars, openly acknowledged its flaw, maintaining an ongoing record of discrepancy. This transparent documentation represents a distinctive method, emphasizing precise tracking of time and celestial occurrences over convenience, providing valuable perspectives into Maya culture and scientific accomplishments.