Concept
819-day count
A Classic Maya interval of 819 days, often tied to a four-part colour and direction scheme. Why 819 mattered was unclear for decades.
Unknown Maya scribe; photograph of a public-domain manuscript, “Dresden Codex, page 49”, Public domain, via Wikimedia Commons
In 2023 Linden and Bricker proposed that 20 such periods, 16,380 days, about 44.85 years, form a common frame for the synodic periods of the visible planets. It is a research proposal, not a settled reconstruction, and it is not evidence of heliocentric orbital mechanics.