02/01/2019

Calendars have regulated human life for millennia.

Reproduction of Marcelo Viana's column in Folha de S.Paulo.

During my childhood I lived in rural villages in northern Portugal. The farmers were almost all illiterate and had no access to newspapers, radio, much less TV. I remember being amazed by their ability to know when it was time to sow or harvest corn, carrots, and other crops. What mysterious "instinct" for time did these simple people possess?

It's no coincidence that the calendar is one of the oldest advancements of civilization. For nomadic hunter-gatherer populations, knowing the time was crucial for tracking the migrations of game species or guiding herds to new pastures. And with sedentarization and the invention of agriculture, it became even more critical to be able to situate the present within the cycles to which our planet is subject, especially the annual and monthly cycles.

Archaeology proves that methods for marking time, for example through the position of the stars, date back to the Neolithic period, between 12,000 and 6,000 years ago. The first known calendars, however, emerged in the Bronze Age, about 5,000 years ago, along with the invention of writing, in Sumeria, Egypt, Babylon, and Assyria.

The main problem with the calendar lies in the fact that the year (Earth's orbit around the Sun) and the month (Movement of the Moon around the Earth) do not correspond to whole numbers of days. In the 11th century, the Persians already knew that a year contains 365.24219858156 days, which is remarkably accurate.

The Babylonian calendar consisted of 12 lunar months, initiated from the observation of the Moon, along with an intercalary period of a few days to complete the year. The Roman Republic used a variation of this calendar, but the fact that the intercalary period was defined by political decree led to abuses, prompting Julius Caesar to reform it. The Julian calendar lasted until the 16th century, when it was gradually replaced by the Gregorian calendar we use today.

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