How the Maya counted Venus, and the book that kept the count
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TL;DR — Maya astronomers put Venus’s cycle as seen from Earth at 584 days, against NASA’s 583.92, using sighting sticks; the Dresden Codex keeps a Venus table.
Maya astronomers measured the cycle of Venus, as seen from Earth, at 584 days. “The Mayan astronomers calculated its synodic period (after which it has returned to the same position) as 584 days,” write J. J. O’Connor and E. F. Robertson in the MacTutor History of Mathematics at the University of St Andrews. NASA’s Venus fact sheet gives the synodic period as 583.92 days, a difference of less than a tenth of a day. The Maya did this with no telescope.
Quick facts
- When
- Classic period, AD 250–900; the Dresden Codex dated by its library to about 1300–1521
- Where
- The Maya lands of southern Mexico and Central America; the codex is now in the Saxon State and University Library, Dresden
- Who
- Maya astronomers and scribes
- Outcome
- They fixed the Venus cycle at 584 days, the year at 365.242 days and the lunar month at 29.5302 days, with no instruments but sighting sticks
Venus as seen from Earth
The 584 days are the planet’s cycle as it appears from the ground, from one appearance in the same position to the next. Its orbit around the Sun is shorter: NASA gives Venus a sidereal orbital period of 224.701 days.
The Maya fitted Venus into their calendar. They kept a cycle of 52 years, and MacTutor points out that “after only two of the 52 years cycles Venus will have made 65 revolutions and also be back to the same position,” a coincidence that “would have meant great celebrations by the Maya every 104 years.”
Two sticks and a tower
Their instruments were simple. “The Mayans carried out astronomical measurements with remarkable accuracy yet they had no instruments other than sticks,” MacTutor says. “They used two sticks in the form of a cross, viewing astronomical objects through the right angle formed by the sticks.”
Buildings helped. “The Caracol building in Chichén Itza is thought by many to be a Mayan observatory,” MacTutor continues; many of its windows line up with the setting sun at the spring equinox and “certain lines of sight relating to the moon.”
The year and the month
The same observers measured the Sun and Moon. “With such crude instruments the Maya were able to calculate the length of the year to be 365.242 days (the modern value is 365.242198 days),” MacTutor notes. At Copán, astronomers “found that 149 lunar months lasted 4400 days,” which gives a month of 29.5302 days; at Palenque they used 81 months to 2,392 days, or 29.5308. The modern value is 29.53059.
The Dresden Codex
The Venus count survives in a book. The Dresden Codex is one of the few Maya books that escaped the Spanish friar Diego de Landa, who, MacTutor records, “ordered all Mayan idols be destroyed and all Mayan books be burned.” Its library, the Saxon State and University Library in Dresden, calls it “the highest quality and the most content-rich codex of the 4 Maya manuscripts preserved worldwide,” made of 39 sheets of bark, with “astronomical and meteorological tables.” The library acquired it in 1739 through its librarian Johann Christian Götze, in Vienna.
Its age is disputed. The library dates it to “the later post-classical period of Maya culture (ca. 1300-1521) on the Yucatán peninsula.” MacTutor instead describes it as “thought to have been copied in the eleventh century AD from an original document dating from the seventh or eighth centuries AD.”
Observation, not mystery
Mark Van Stone, writing for the Foundation for the Advancement of Mesoamerican Studies, rejects claims that Maya astronomy came from hidden or extraterrestrial knowledge. “This is simply not true,” he writes. “They simply used the tools they had at hand, and their penetrating, persistent intelligence to do the best they could.” The Maya numbers and zero that carried these counts are described in a separate article.
Key facts
- Maya astronomers put the synodic period of Venus at 584 days; NASA gives 583.92 (MacTutor; NASA).
- Two 52-year cycles, 104 years, equal 65 Venus cycles (MacTutor).
- They measured the year at 365.242 days and, at Copán, 149 lunar months at 4,400 days (MacTutor).
- Their only instruments were sighting sticks set in a cross (MacTutor).
- The Dresden Codex, of 39 bark sheets, was acquired in 1739 and is dated by its library to about 1300–1521 (SLUB Dresden).
- MacTutor gives a different date: an 11th-century copy of a seventh- or eighth-century original.
FAQ
How did the Maya track Venus without a telescope?
By sighting with two crossed sticks and keeping written records. MacTutor says they had "no instruments other than sticks."
How accurate was the Maya Venus cycle?
They put it at 584 days. NASA's figure for the synodic period of Venus is 583.92 days.
What is the Dresden Codex?
A Maya book of 39 bark sheets, with ritual calendars and astronomical tables including a Venus table, kept by the Saxon State and University Library in Dresden since 1739.
How old is the Dresden Codex?
Its library dates it to about 1300–1521, in the late Postclassic period. MacTutor gives an older estimate, an 11th-century copy of an original from the seventh or eighth century.
Was El Caracol an observatory?
Many think so. Several of its windows line up with the sunset at the spring equinox and with lines of sight to the Moon, according to MacTutor.
Sources
Cite this article
- APA
- Song Letter. (2026, October 11). How the Maya counted Venus, and the book that kept the count. Our Earth's History. https://ourearthshistory.com/americas/medieval/maya-venus-cycle-dresden-codex-naked-eye/
- Chicago
- Song Letter. “How the Maya counted Venus, and the book that kept the count.” Our Earth's History, October 11, 2026. https://ourearthshistory.com/americas/medieval/maya-venus-cycle-dresden-codex-naked-eye/.
- MLA
- Song Letter. “How the Maya counted Venus, and the book that kept the count.” Our Earth's History, 11 Oct. 2026, https://ourearthshistory.com/americas/medieval/maya-venus-cycle-dresden-codex-naked-eye/.
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