The Maya used several calendars: a ritual calendar (Tzolk'in) of 260 days and a solar year calendar (Haab) of 365 days.
The Tzolk'in resulted from the permutation of 13 numbers with a fixed sequence of 20 day names (or day gods). It was used for divination and to determine rituals.
The Haab consisted of 18 months of 20 days each plus 5 leap days at the end of the year. It was mainly used to give exact historical dates and for astronomical and meteorological calculations.
If one combines the counting of the Tzolk'in with that of the Haab according to the principle of two interlocking, i.e. counter-rotating, cogwheels, the same combination is repeated every 52 years. This "calendar round" can be regarded as the Central American counterpart to our century.
In 1887 Ernst Wilhelm Förstemann (1822-1906), director of the Royal Public Library in Dresden, discovered the principle of the Long Count on the basis of the 'Dresden Codex', using the names of the days and months handed down by Diego de Landa, whereby the Maya indicated the number of days that had passed since the creation date 4 Ajaw 8 Kumk'u. This Tzolk'in-Haab starting constellation returns after 1,872,000 days (13 Bak'tun in the Maya number system), i.e. approximately every 5,125 solar years.
In 1897, the American journalist Joseph Goodman (1838-1917) succeeded in establishing a correlation of the Mayan calendar with the Gregorian calendar, still widely accepted today. According to this, the Mayan zero date corresponds to the year 3114 BC.
The return of the date 4 Ajaw 8 Kumk'u after 13 Bak'tun periods on December 21, 2012 caused many spiritists and apocalypticists to fear the end of the world due to a wrong interpretation of an inscription on a Mayan stele from Tortuguero and the flood scene in the Dresden Codex. In truth, however, the date is comparable to a turn of a millennium in our culture.