Correlations

The Maya Long Count and the Gregorian calendar are both extremely accurate. Each is able to distinguish any given day from any other in history. To convert Gregorian dates to Long Count, or vice versa, only one day needs to be established in the calendar system of the other. Traditionally, this is done by establishing an offset (correlation constant) of a given number of days from the start of the Julian Period to the zero date of the Long Count.

Unfortunately, the Long Count was no longer used by the Maya at the time of the Spanish Conquest, because then a definitive correlation constant could be determined. By that time, dates were abbreviated by use of the Calendar Round and Short Count.

Several correlations have been proposed. Each is named for the person who proposed it, except for the Astronomical (584285) correlation that was proposed by Thompson. He later rejected it in favor of the GMT (Goodman, Martinez, Thompson) correlation, but the record of astronomical events recorded by the Maya during the Classic Period show it to have the highest probability of being correct. By examining the various pieces of historical, anthropological, archeological, and astronomical evidence, only a few correlations have any argument for their use. Correlation Constants table

Maya scholars usually use only two the GMT (584283) and Astronomical (584285) correlations. The GMT (named by Goodman, Martinez, and Thompson) correlation corresponds best to dates in use by Maya at the time of the conquest. The Astronomical correlation matches the astronomical information the best. Most scholars today use the Astronomical correlation in their publications. The Spinden and Valliant have had some arguments for them, but have been largely discredited. The other correlations are mere novelties with virtually no adherents. Authors generally state somewhere within their text which correlation constant they use to specify Gregorian or Julian dates.