Kin

The kin is the base unit of the Maya Long Count, the great linear calendar the Maya used to fix dates across vast spans of time rather than within a repeating cycle. A kin is a single day. The Long Count builds larger units from it in a mostly base-twenty scheme: twenty kins make the next unit up, and successive units multiply by twenty, with one deliberate exception at the third level to keep the count close to the solar year. A Long Count date is written as a string of these units counted from a fixed mythic starting point, the creation date the inscriptions give as 4 Ajaw 8 Kumku. The kin is thus the atom of the whole system. These are the features of the Maya Long Count, the timekeeping framework carved on the monuments of the Classic period to record the reigns and rituals of the Maya lords.

The Kin is the base unit of the Maya Long Count, a single solar day, and the Long Count itself is a positional, largely base-20 (vigesimal) tally of elapsed days written as five place values, Baktun.Katun.Tun.Winal.Kin, running for example 13.0.0.0.0. Long Count dates are attested in monumental inscriptions from the Preclassic period onward, with the earliest securely dated examples from sites such as Chiapa de Corzo and Tres Zapotes in the last centuries BCE, predating the Classic Maya cities where the system is best known. Because the count is a simple linear tally from a fixed starting point rather than a cycle that repeats, it can in principle run indefinitely, and it is the only calendar among the Mesoamerican systems capable of specifying a date uniquely across long spans rather than only within a repeating 52-year or 18,980-day round.

Because the kin is a single day and the Long Count is a plain tally of kins from a fixed origin, converting a Maya date into a European one reduces to a single unknown: how many days lie between the Long Count origin and some fixed point in the Julian day count. That number is the correlation constant, and choosing it correctly is the whole of the problem.

The value in general use is 584,283, the Goodman, Martinez and Thompson correlation, usually shortened to the GMT correlation, which places the Long Count origin 13.0.0.0.0, 4 Ajaw 8 Kumku, in August of 3114 BCE in the proleptic Gregorian calendar. It is supported by several independent lines of evidence, among them the alignment of Classic eclipse and Venus records with computed astronomy, the continuity of the 260-day count kept by highland Maya daykeepers, and radiocarbon dates from dated monuments and lintels.

A small number of competing constants have been proposed and continue to be argued for, differing by a few days or by rather more, and the debate is a live one rather than a settled point of history. What is not in dispute is the structure being correlated: the count of kins itself is unambiguous, and any correlation shifts every Maya date by the same amount.