Scientists at Tulane University in Louisiana have solved the mystery of the 819-day ancient Mesoamerican calendar used by ancient Mayans.

The researchers were able to match the planetary cycles of every planet that might have been visible to ancient astronomers using a 45-year period.

Multiple calendars that were likely used by scholars at the time have been discovered during research on the ancient Mayan civilization, but not all of them make sense in today’s world. One such calendar was discovered in glyphic texts – the Mayans’ native writing system – and piqued the interest of researchers.

However, the astronomers did not leave behind any additional text or definitions explaining how it might work with their regular calendar system.