To the modern stargazer, the planet Venus is just another point of light in the night sky. But for the ancient Maya, the brilliant light of Venus was an omen of war that guided ritual activity, prompted great battles, and was even used as shorthand for “total destruction.”

Archaeologists have long looked to Venus to understand Maya calendars and tradition. But now, a fresh look at an ancient text called the Dresden Codex suggests that our understanding of how the Maya tracked Venus for their celestial calendars may be all wrong.

By combining a new reading of the text, tricky mathematical equations, and field observations, Gerardo Aldana at the University of California, Santa Barbara has simplified the way Maya scribes would have corrected their calendars.

“There is some really elegant math that’s going on there that has not been recognized before,” says Aldana.

His work not only casts new light on how the Maya tied their ceremonies to the sky, it may also call into question every date we have for events in the ancient Maya world. (Also see “Teen's 'Discovery' of Maya City Is a Very Western Mistake.”)

Celestial Fix

Scientists have long known that ancient Mesoamerican cultures were fascinated with the night sky, but many details of how they tracked celestial objects were lost to the ravages of time and conquest. The Dresden Codex (named for the European city in which it has been housed since the mid-1700s) is one of four texts remaining out of thousands that existed before Europeans arrived in the New World.

Like many of these precious books, the Dresden Codex has been examined and reexamined countless times by archaeologists and other experts skilled in deciphering ancient texts. A favorite section has been the so-called Venus tables, which provided ancient skygazers with a correction tool for their calendars.

Ancient Mesoamericans used two interlocking yet unrelated calendar cycles. The 365-day solar calendar, called the haab, tracked the movement of the sun, while a second ceremonial one called the tzolkin followed a 260-day track linked to ceremonies and celebrations. Think of it like the days of the week, if a week lasted 260 days and each day had its own cultural significance.

However, since the actual solar year is 365.25 days long, the Maya had to correct for the extra quarter day, just as we do now by adding leap days to the calendar every four years. (Read about the surprising history of the leap year).

To make their corrections, the Maya used the planet Venus. Looking through their ancient texts, they could tell where Venus was on a particular day hundreds of years before, and thus where it should have been at the time someone looked in the sky. The difference was the amount of correction necessary.

But it’s not as easy as that. For more than a hundred years, experts have reconstructed the equations the Maya would have used, based partly on the Dresden Codex. What they landed on is a complex series of patches and changes that create a hyper-precise calendar system similar to our own.

Aldana’s latest work has thrown that picture into question. An engineer as well as an archaeologist, he dove into the text and reinterpreted a single word, k’al—which had been assumed to mean “to tie or bind”—to mean “to enclose.”

That small shift changed how the math might have been done. His version is simpler than the previous interpretations, but it creates a calendar that’s less accurate.

Venus, Warrior Planet?

Aldana says this new reading suggests the Maya were less concerned about precision and more concerned with preserving their 260-day ceremonial calendar. He compares it to the Catholic church’s struggle in the 16th century to create an accurate calendar to guide Easter celebrations, efforts which ultimately gave us the Gregorian calendar still in use today.

“Their ability to predict the stars’ positions was affecting their ability to plan their religious events,” he says. His work thus moves Maya star-gazing “more into the realm of state-sponsored ritual—of large-scale ceremony.”

Maya "Underworld" Observatory Revealed In a cave in Mexico's Yucatán, a National Geographic explorer reveals what is believed to have been an underground observatory for witnessing the zenith passage of the sun.

It’s no small thing, since for decades the Maya have been popularly known as precision astronomers who used the sky to predict the future. And they were not the only Mesoamericans who tracked things like Venus.

“Venus imagery goes back to the pre-Classic. Even the Olmec have a Venus symbol,” says archaeologist Francisco Estrada-Belli of Boston University, referring to the parent civilization of several Mesoamerican cultures. For instance, Teotihuacan, a massive ancient city center near today’s Mexico City, was a contemporary of the Classic Maya empire (A.D. 250-900), and experts have suggested that its three major structures were laid out to conform with the cycles of the sun, the moon, and Venus.

Archaeologists have even long wondered if the Maya, the Mexica, and the people of Teotihuacan shared a Venus-related warrior cult, in which the planet’s movements guided military strategy.

Venus seems to have played a role in long-held rivalry between the two signature powers of the Classic Maya: Tikal and the Kaanul, or Snake, dynasty. Some say their earliest definitive battle, in April of the year 562, may have been timed in accordance with Venus. (Read more about the Snake kings and the search for a lost Maya empire.)

At the very least, the planet was an ominous sign. When one army completely demolished another, as the Snakes did to Tikal that day, scribes would describe the victory by adding a symbol for Venus to indicate “total destruction.”

But if Aldana is correct, we might have to change the dates for such epic clashes, because their calendar and ours might now be out of sync.

Universal Language

Harvey Bricker, an emeritus professor at Tulane University, agrees that the Maya corrected their calendars by tracking Venus and that the calendars had ceremonial purposes, but he sees no reason that they would have favored the ceremonial calendar. He also cautions against tweaking the existing Maya calendar until there is stronger evidence that we require such a change.

“The fact that [the current system of correction] is used by others is not because it is popular, but rather because there is solid historical and astronomical evidence that it is the correct one,” he writes in an email. “Failure to use it is a fatal flaw in Dr. Aldana's research.”

Aldana says his work doesn’t have to affect any established dates; that’s only a possibility. For him, the most thrilling part of this work had nothing to do with its interpretation but rather with the cold, hard math.

As he worked on the Dresden Codex, he felt a kinship with the ancient unnamed scholar who was wrestling with the same equations. Understanding the math, he says, helped him understand the people.

“It’s the language of math that you are speaking through,” he says, “and that’s just really profound.”