The First Timekeepers

The History of the Calendar

The calendar is such a fundamental part of the way that modern society functions that it is scarcely even thought about. But the modern Gregorian calendar is less than 500 years old, and has only been used in the English speaking world since 1752, and did not become the global standard until the later half of the 1800s. Several countries have still yet to adopt it, using other calendar systems entirely.

For instance, Ethiopia, the second most populous country of Africa and home to more people than the UK, uses its own calendar, divided into twelve months of equal length, and a thirteenth month just six days long. Iran and Afghanistan have adopted the “Solar Hijri”, with six 31 day months followed by five 30 day months and one 29 day month, which is 30 days long in leap years. Even India, with a population four times that of the United States, uses the unique Saka calendar, similar to the Solar Hijri. Nepal uses the Vikram Samvat, North Korea uses the Juche, Thailand uses the Suriyakti, Myanmar uses the Burmese, and Taiwan uses the Minguo. That’s not even to mention the dozens of religious calendars used by various churches, mosques, and temples, throughout the world.

With nine countries and a combined population of over 1.6 billion employing different calendars, more than one in five humans use at least one calendar entirely unfamiliar to just about everybody in Europe and America. But all of the civil calendars in modern use are similar in several key ways. All but one of them divide years into 12 months of roughly equal length. They all feature leap days once every four years. They are all so accurate that they will remain in sync with the seasons for millennia. Why is it that these nine calendars are so similar? How did they develop, and influence each other? Why are all of them based on the Earth’s orbit around the sun, rather than the moon’s orbit around Earth, or some more arbitrary system?

This series will cover the history of the calendar, from before the creation of the written language to after the creation of the internet.

The First Timekeepers: The Origin of Days, Months, and Years

Timekeeping is not unique to humans. Thousands of species of virtually every group of animal life migrate from place to place as temperatures and weather change in an endless yearly cycle. Even more widespread are daily circadian rhythms, which modify the behavior of virtually all of life on Earth, even mindless plants and fungi. Even bacteria, the smallest and simplest organisms on the planet, possess these rhythms.

All humans naturally possess a circadian rhythm based on sunlight, resulting in us becoming more tired following sunset. Artificial lights that mimic sunlight, from fireplaces to computer screens, can result in this rhythm shifting, a major cause of insomnia worldwide. The “jet lag” experienced by air travelers is also a result of circadian disruption. With its massive impact on human behavior and bodily function, it is only natural to divide time into days. But humans do not instinctively migrate from place to place, and we certainly do not migrate in yearly cycles.

But even staying in one place for your entire life, knowing what time of the year it is crucial to survival and wellbeing. Summer and Fall bring with them an abundance of food, while Winter and Spring have comparatively far less available for consumption. Being able to know exactly what time of year it is means that you can make preparations for future conditions, such as storing extra food in fall so as not to starve the following winter. But since weather is somewhat random, it isn’t possible to get an accurate measurement of the year simply by counting the days between, say, the first time it snows one winter and the first time it snows the following winter.

The moon provides us with a simple alternative. The Earth casts a shadow on the moon as it orbits the planet, resulting in its appearance varying from the circular full moon, to the sickle shaped crescent moon, to the practically invisible new moon. The motion of the moon around the Earth is regular, following cycles which are around 29 and a half days in length. Early peoples around the world tried to count the number of these cycles in a year, and reached an approximation of 12.

This is the origin of the idea of a “month”, and is the reason why nearly all modern calendars have 12 of them. The Proto-Germanic people of modern day Scandinavia and northern Germany 2500 years ago called the moon “ᛗᛖᚾᛟᚾ” (May-nawn) and each cycle was a “ᛗᛖᚾᛟᚦ.” (May-nawth) That’s only a one letter difference. The Anglo-Saxons, descended from the Proto-Germans, arrived in British isles around 1000 years later. They called each cycle a “Monað” (Mow-nawth). Their English descendants slightly modified the spelling and pronunciation to the modern “Month.”

But even still, twelve lunar months is far from perfect in matching the length of the solar year. Twelve lunar months occur in 354 days, meaning that this system for measuring the length of the year is off by about 3%. That is so inaccurate that it is practically useless. If someone was born near the beginning of Winter, they would turn 20 in the middle of summer according to that system. Because of this, “lunar calendars” are not used to determine the time of year. However, they continue to see religious usage, most significantly in the Hijri calendar used to calculate the time of holidays and rituals in Islam.

This problem became obvious almost immediately after the concept of months came into use, and ancient peoples who wished to measure time needed to find a solution. That solution came with the discovery of the ecliptic. The Earth orbits the sun in an elliptical orbital plane, while also rotating about its axis. The axis is not perpendicular to the orbital plane though, but is instead tilted about 23.4 degrees. This means that at different times of year, the day will be longer or shorter. Summer has more sunlight, leading to higher temperatures, while the opposite is true of Winter.

But more importantly to the history of the calendar, this causes the sun to appear to rise and set in different locations over the course of the year, slightly north or slightly south, rather than due east. Even though they thought the sun went around the Earth, the stone age peoples of Europe still noticed this effect. They realized that these differences followed a yearly cycle. The point at which the sun rose furthest in the south is the Winter Solstice, the shortest day in the year.

The Warren Field, built in modern day Scotland 10,000 years ago, is the oldest known calendar, and it uses both the phases of the moon and winter solstice to calculate the time of year. Discovered in 2004 and described in archaeology journals in 2013, it looks nothing like any calendar we would use today. It is a sequence of 12 pits around 40 meters long. The pits follow an arc, which is almost exactly perpendicular with the path of the sun only on the morning of the winter solstice. Doing this, the stone age scots could determine when exactly one year had passed.

As the moon cycled through its phases, a stake would be moved from pit to pit, and on the Winter solstice, it would be moved back from the twelfth pit to the first one. Being based on both the motion of the moon and the sun, this was the first “lunisolar” calendar. In a world without the ability to perform mathematical calculations, it is hard to imagine a more accurate and reliable system.

But megaliths the size of airplanes, only specific down to the month, that have to be adjusted every year to remain in sync, still don’t make a very good system. It certainly doesn’t make the system we use today, or anything close to it. It doesn’t even have the concept of weeks, much less the names of different days of the week, and if the stone age Scots had names for the months, they have been lost to history.