We gather much of what we know about Maya astronomical knowledge from detailed records they themselves created on the pages of bark-paper books called codices. In the mid-sixteenth century, Franciscan missionaries burned nearly all of the Maya’s written records in an effort to eradicate their religion. Today, only three or four Maya codices remain. Three of them are named for the European cities where they are kept—Dresden, Paris, and Madrid. The authenticity of a fourth book called the Grolier Codex, now in Mexico City, is still disputed. The codices were probably written no earlier than the twelfth century A.D., but the Maya may have copied books that were written much earlier. According to archaeoastronomer Anthony Aveni, the codices were used to set dates for rituals, often by linking them to astronomical events.

The pages of the codices usually depict a deity and include a series of glyphs describing what the deity is doing. Many pages of these books also contain lists of numbers that allowed the Maya to predict lunar and solar eclipses, the phases of the moon, and movements of Mars and Venus. One example is a series of three pages in the Dresden Codex that record the phases of Venus as well as a list of tzolk’in dates and glyphs that have to do with omens and augury. The Maya believed that Venus was associated with violence and bad luck at certain times of the year. That association is clear on the second page in the series, which shows an image of the god Kukulcan, representing Venus, in the process of spearing an enemy.

The sun and the moon were not the only celestial bodies of importance to the ancient Maya. The movements of the planet Venus also held special meaning for them. Tables that mark Venus’ position throughout the year are recorded in ancient Maya books called codices and on monuments throughout the Maya kingdoms. Venus also seems to have influenced the architecture of the city Uxmal in the northwestern part of Yucatán, Mexico. Anthony Aveni, an archaeoastronomer at Colgate University, believes that the royal residence named the “House of the Governor” was designed with the observation of Venus in mind. Venus symbols decorate its façade and from its central doorway an observer can still see the planet align with monuments across the site that mark the northern and southern extremes of Venus’ migration along the horizon throughout the year.

Venus orbits the sun approximately every 225 days, but as it is seen from Earth, the planet appears to move back and forth relative to the sun in a cycle that lasts 584 days. Five of these oscillations—2,920 days—are almost exactly as long as eight solar years. Aveni believes that Maya priests saw significance in this astronomical coincidence. “For the Maya, everything has to be brought together in terms of whole multiples and that’s where Venus comes in. It has a five-to-eight rhythm with the sun,” says Aveni.

Venus also appears to go through four phases. For 250 days the planet is known in Western cultures as the “Evening Star” as it follows the setting sun. After the Evening Star phase, Venus disappears for eight days before returning as the “Morning Star”—the 236-day-long phase when it rises just before dawn. After the Morning Star phase, Venus disappears for 90 days before returning again as the Evening Star. A document from Central Mexico written in the late 1500s called the Annals of Cuauhtitlan associates the eight-day period between the Evening and Morning Star phases with the death and resurrection of Quetzalcoatl, a deity known as Kukulcan to the ancient Maya. Kukulcan was the sky god and the most powerful of the ancient Maya deities. According to Aveni, rituals celebrating the appearance of the Morning Star may have been held on the large plaza in front of the House of the Governor, providing the rulers of Uxmal with a way to commemorate their ties to the sky god.

The Long Count calendar may be a relic of the past, but modern-day Maya communities in the highlands of Guatemala still have “Daykeepers,” people whose job it is to maintain a 260-day ritual calendar. Allen Christenson, an anthropologist at Brigham Young University, apprenticed himself to a Daykeeper to gain a better understanding of Maya concepts of time and the cosmos. According to Christenson, the Daykeepers’ role in the community is to keep track of different cycles of time, to perform the proper rituals to keep the cycles running, and to heal people when they are sick. The 260-day calendar they use today is the same as the tzolk’in calendar used by the Maya 1,000 years ago, although the modern calendar is shifted two days later than the ancient one. One concept that seems strange to the Daykeepers with whom Christenson has worked is the idea that some kind of apocalypse is going to happen on December 23, 2012. Until recently the highland Maya had little or no knowledge of the predictions regarding the 2012 date, but that doesn’t mean that they don’t think the world will end. “The world is going die on December 23,” says Christenson, explaining that the Maya believe the world dies each day when the sun sets, or when crops are harvested. “The world is constantly dying,” he says, “and the role of the Daykeeper is to make sure they get things going again.”