The day on which the current baktun of the Maya Long Count will end is -- as said before -- still something of a matter of debate. Depending on the book, the current baktun will end on December 21, 2012, on December 23, 2012 or on December 22, 2012. Why don’t these books agree?
Matching up -- or correlating -- the Maya’s Long Count and Calendar Round with our calendar is a study filled with a variety of gathered clues, disagreeing factions and even a plethora of mathematical programs used to aid calculation. Various theories are still employed for correlation and lines have been drawn as people are still trying to refine the match between our calendar and those of the ancient Maya.
The Main Correlations
Currently, two main correlations exist for matching up our calendar with the ancient Mayans’ calendars. These are the Spinden Correlation (also called the 11.16 Correlation) and the Thompson Correlation (also called the 12.9 Correlation, the Goodman-Martinez-Thompson Correlation or the GMT).
The Spinden Correlation fits very well with what archaeologists have found in the northern area of the Yucatan -- but nowhere else. The Thompson Correlation however – which places dates 260 years later than the Spinden Correlation -- fits better with what archaeologists have found everywhere else. Of the two correlations, the Thompson Correlation is more accepted in Maya studies.
However, a third notable correlation exists, created by George Vaillant. It is known as the 11.3 correlation. Some people who study the Maya keep an open mind about this correlation.
Short Count Correlation Clue
So far, it is not possible to directly make a correlation of the Long Count with our calendar. Instead, direct correlation is made with the Short Count, a shorter version of the Long Count, found in such places as books written after contact with the Spanish, such as the books of Chilam Balam. One such date correlation found in these books matches the Short Count date Katun 13 Ahau with January 6, 1542 -- the day the city of Merida was founded.
This is not a perfect clue however. There is still the issue of making the Long Count match the Short Count -- and the fact that a person using the Short Count dates assumes that it is still in sync with the Long Count.
Post-Spanish contact information isn’t the only kind of clue found in old artifacts. Lunar eclipse information in the Dresden Codex is another piece of information people use to correlate the Mayan calendars to ours. People use this information by calculating backwards when lunar eclipses would have occurred.
Correlation Clues via Carbon Dating
Archaeologists have been collecting clues for date correlation while in the field. An example of this is the carbon dating of sapodilla lintels at Tikal. The first time they did this, the Spinden Correlation seemed to be right. However, when they tested the lintels again the Thompson Correlation seemed the most right, matching with 10 of the 12 wood samples they used.
When making the attempt to correlate the calendars, there are several other things that a person must consider. One of these considerations is the ancient Maya concept of a day – which is understood to have gone from sunset to sunset and not midnight to midnight like with today. Also unlike our concept of a day, the Maya did not give the day its number until it was over.
"The Ancient Maya", 5th Edition; Michael C. Coe;
Dartmouth College: Izapa: Birthplace of Time: Correlation
“The Ancient Maya”; Robert J. Sharer, Loa P. Traxler; 2006