Maya astronomical tables found daubed on wall

Archaeologists have discovered a 9th-century Mayan house with astronomical tables inscribed on the walls. The tables suggest that the Mesoamerican civilisation had advanced astronomy for over 1000 years, and that the information was widely available in Mayan society.

Until now our main evidence of Mayan astronomical knowledge came from books produced centuries after their society declined. The most famous is theDresden Codex, which dates from the 11th or 12th century. "The Dresden Codex was the summit – artistically, calligraphically, and intellectually," saysStephen Houston of Brown University in Providence, Rhode Island.

But the Maya civilisation reached its height centuries before that. The Classic period spanned AD 250-900 and saw the rise of major cities – including Tikalin what is now Guatemala – and the construction of vast stepped pyramids.

No Classic astronomical texts survive, because Mayan books were made of plaster and bark paper that have rotted away, says William Saturno of Boston University in Massachusetts.

Dig for astronomy

In 2010 Saturno and colleagues were excavating Mayan ruins at Xultún, also in Guatemala. One house had been partially looted, exposing a mural on one wall. Intrigued, Saturno excavated the rest of the building.

The walls were covered with pictures of Mayan people. In the gaps between the drawings, and sometimes drawn over the top of them, were glyphs: Mayan writing. Two sets looked like Dresden Codex glyphs, and contained astronomical information.

The first is a table describing lunar cycles: the 29.5 days it takes for the moon to go through all of its phases. The Maya believed in six gods of the moon, each ruling its own lunar cycle. By knowing which god was in charge of the moon at any given time, Mayan rulers could plan their actions accordingly. "The Maya doubtless started with a presumption of meaning in such movements," explains Houston.

Mayan society was dominated by the idea that time is cyclic. "The Maya conceived of time as a series of cycles that all interplay and all repeat," Saturno says. By understanding these repetitions, including astronomical cycles, they picked the most auspicious dates for events, such as coronations.

1000-year-long calculation

The second set of glyphs is more obscure. Saturno thinks it relates to two Mayan calendars: a ritual calendar lasting 260 days and the solar calendar, lasting 365 days. The two calendars only show the same date once every 18,980 days – the so-called Calendar Round.

All the numbers in the second set are multiples of 18,980, suggesting they are anniversaries. They are also multiples of other astronomical cycles. But Saturno doesn't know what they represent.

"It seems obvious that the Maya were making almanacs, major calculations, and Dresden Codex-like astronomical tables for over 1000 years," says Joyce Marcus of the University of Michigan in Ann Arbor.

The house probably belonged to a senior figure but not a royal. That suggests astronomical information was broadly available in Mayan society, says Gary Feinman of the Field Museum in Chicago, Illinois.

Journal reference: Science, DOI: 10.1126/science.1221444