The 260-day Tzolkin harmonic

The Tzolk'in, to use the modern Yucatec-based coinage for it, is a cycle of 260 days produced by running the numbers one to thirteen against twenty named days, so that a given number-and-name pair recurs every 260 days. It is the oldest continuously used calendar in the Americas: 260-day counts are attested in Zapotec inscriptions from Monte Alban by the sixth century BCE and are shared across Mesoamerica, appearing among the Mixtec, the Aztec, who called their version the tonalpohualli, and the Maya.

Meshed with the 365-day Haab, it produces the Calendar Round of 18,980 days, about fifty-two years, after which a full date repeats. The origin of the number 260 is debated: proposals include the approximate human gestation period, the interval between zenith passages of the Sun at certain Mesoamerican latitudes, and the product of the ritually significant numbers thirteen and twenty. No single explanation is established.

The Dreamspell keeps the arithmetic, thirteen tones against twenty seals giving 260 kin, and replaces almost everything else. The day names are renamed, the numbers are recast as Galactic Tones with new keywords, a colour and a direction are assigned to each seal on a four-part rotation, and the whole is locked to the Gregorian year by a fixed correlation with the leap day omitted. Because of that omission the Dreamspell kin for a given date and the traditional kin for the same date diverge permanently, so the two cannot be treated as versions of one thing.

The traditional count is also not tied to the Gregorian calendar at all; it simply runs, and the correlation between the Maya Long Count and the Christian era, the GMT correlation constant, is a technical question in Mayanist scholarship settled on epigraphic, astronomical and radiocarbon grounds rather than by preference. Anyone wanting the day sign a Guatemalan daykeeper would give must use the traditional count, not this one.