Calendars
Using this astronomical information, Mayan priests devised a layered calendar system. There is the agricultural/solar year Haab' cycle that consists of 365 days, split into 18 20-day months and a period of 5 nameless (and potentially unlucky) days called Uayeb/Wayeb. Ceremonies like Sac Ha', Cha'a Chac and Wajikol are often performed during this period. Additionally, the Tzolk'in, or "Sacred Round," is a ritual cycle consisting of 260 unique days. This cycle specifically follows the nine moon cycles and the birth period of a child. No combination of a Haab' day and Tzolk'in day will repeat until after 52 Haab' cycles, which is known as the Calendar Round. This is a broad and basic description of a complex system that has many other components and nuances.
Painting of the Tzolk'in Cycle by Patricia Martin Morales
This is a contemporary painting by artist Patricia Martin Morales and not a codex page, but the image of two rings is helpful towards visualizing the 260 unique days of the Tzolk'in cycle. The outer ring contains 20 day glyphs and the inner ring consists of 13 numbers. Each glyph combines with each number once in a Tzolk'in cycle, with all possible combinations summing up to 260 unique days.
Pages 19 and 20 of the Paris Codex (Year Bearers)
These pages of the Paris codex contain depictions of year-bearers, or the namesake and carriers of a given year. Within a Calendar Round there are four year-bearers that rotate. The names included in the Paris codex are Ak'bal, Lamat, B'en, and Etz'nab. On these particular pages, the vertical glyphs correspond with B'en years (left page) and Ak'bal years (right page). Each year-bearer has attached meanings and associations (luck, doubt, abundance, etc.) that act as predictions for the events of their year.
Pages 75 and 76 of the Madrid Codex (Cosmogram)
These pages from the Madrid Codex showcase a four-part cosmogram that combines elements of the Tzolk'in and Haab' cycles, meaning it can be interpreted as referencing the Calendar Round. At each of the four corners deities are making offerings towards the center, where two creator gods are seated. They are surrounded by a square containing the 20 Tzolk'in day glyphs.
Page 56 of the Dresden Codex (Lunar Series)
This final page from the Dresden codex is one of multiple making up the Lunar series/Eclipse table. There is a strong tie between the mathematics in this series and the Long Count, a calendar used for events surpassing the span of a Calendar Round. A Long Count date is made up of 5 numbers. These are Kin (a day), Uinal (20 kin), Tun (360 kin), Katun (7,200 kin), and Baktun (144,000 kin). The beginning of the Long Count and Great Cycle was deciphered as "13.0.0.0.0, 4 Ahau, 8 Cumku," meaning 13 Baktun (the completed days from the previous Long Count cycle) with the corresponding Tzolk'in and Haab' dates. On the Gregorian Calendar, this has been interpreted as August 11, 3114 BCE.