Author’s Note: This is part one of a series on the Maya calendars. Each section in this post will eventually have a separate post which I will hyperlink to its respective header.
In Mesoamerica -- possibly in Izapa during the 1300s BC -- two calendars developed, a sacred calendar and a calendar based on the sun. These calendars spread to peoples including the Mixtecs, Teotihuacanos and Zapotecs as well as the ancient Maya, who used the two calendars in an interlocking system.
Of the peoples that used it, the ancient Maya are believed to be the people who refined the system the most. Other than the two calendars, they also kept other “calendars”.
The Sacred Calendar: Tzolkin
The sacred calendar -- which was used for religious purposes -- is known today as the Tzolkin. This calendar has an interlocked cycle of 13 numbers and 20 days that started over after 260 days (13 x 20 = 260). Each of the 20 days had a name.
The Sun-Based Calendar: Haab
The sun-based calendar -- which was used for more everyday purposes -- is known today as the vague year or the Haab, and was like our calendar. Made up in total of 365 days, the Haab contains 18 months, each having 20 days, plus a group of 5 days (18 x 20 + 5 = 365). Each month of the Haab, like our calendar (the Gregorian calendar), has a name.
Calendar Round: The Interlocking System
The Calendar Round is the name that people who study the Maya use to describe the interlocking system of the Tzolkin and the Haab. The cycle produced by combining these two calendars repeats every 52 years.
The Long Count is a system of units for keeping track of how many days had passed since the creation of the current world. Something only the Maya used, unlike the Haab and Tzolkin, the Long Count does not repeat, but continues to go up in number. Its smallest unit was a day from which it progressed to larger and larger units. Currently, the Long Count’s start date is thought to be sometime in 3114 BC.
The ancient Maya also used some other cycles, and worked them into their timekeeping. Some of these cycles are the cycle of Venus, an 819-day count centered on the god K’awiil and the cycle of the moon as well as the cycle of the Nine Lords of Night.
Through the years, various people tried to find a date or dates to match our calendar with the ancient Mayan Calendar Round and Long Count. So far, a match known as the Gordon-Martinez-Thompson correlation (or GMT correlation) is the most commonly accepted as the right match. However, not everyone thinks it is as accurate as it ought to be.
"A Forest of Kings"; Linda Schele, David Friedel; 1990
Dartmouth College: Chapter 6 The Long Count: Astronomical Precision
"The Ancient Maya"; Robert J. Sharer, Loa P. Traxler; 2006