As we hang up our 2026 calendars, it seems a perfect time to recall that Mexico’s ancient ancestors long ago devised a remarkably accurate calendar system, closely approximating the modern calculation of Earth’s annual rotation around the Sun.
The Mexica solar year averaged 365.2420 days—far more precise than Europe’s Julian calendar of the same era and razor-close to today’s value of 365.2422 days. This precision was achieved through consistent astronomical observation and a deep understanding of Earth’s natural phenomena.
The Mexica measured time using two interlocking calendars:
First, the Xiuhpohualli (“year count”), a 365-day solar calendar divided into 18 months of 20 days, aligned with agricultural cycles, plus five “empty” nemontemi days.
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