How Calendars Evolved

Anmol Mohan
"Most modern calendars mar the sweet simplicity of our lives by reminding us that each day that passes is the anniversary of some perfectly uninteresting event."
― Oscar Wilde

Calendars are interesting. They keep our schedules in check, remind us of what is essential, and help us plan. In short, they are a tool to manage the most critical resource of our lives, time.

As we celebrate leap year, I thought maybe we should look at how Calendar's evolved. Do you know that even though the year 2000 was a leap year but 1900 was not and 2100 would not? That is because we only need to add 97 days over 400 years to keep up with the exact amount of days required. So yes, if a year is divisible by 4, a day is added. But if a year is also divisible by 100, it has to be divisible by 400 as well for it to be a leap year.

Early Calendars

There is much debate about the inception of calendars. Humans are pattern mining machines, and ever since we started observing things, we are enchanted by the cyclical elements.

Stonehenge is an example of how astronomical alignment was used to track periodicity.

The first calendars were most likely invented in ancient Egypt at the dawn of agriculture. The priests of Egyptian Civilization were experts in astronomy. They were very observant about the reappearance of the star Sirius dedicated to their god Sothis. The priests observed that annual floods in the River Nile escorted the rise of Sirius over the east. As the Nile was the life-blood of the entire Civilization, it made sense to keep track of Sirius to predict and plan for the flood. This annual rote came to be known as the Sothic year.

The Roman Calendar

However, the modern, almost universally accepted Calendar has its roots in the Roman era. The early Romans who learned to keep the cycles from Greeks were using a 300-day calendar, having 30 or 31 days each. The remaining 50 odd days of the year were called 'winter.'

Mr. Pythagoras, who is famous for his theorem, also made several changes to the old Roman Calendar. He introduced two new months, so now the Calendar had 12 months. It becomes evident if you observe that the root of October is Octa, which means eight, yet it is the 10th month of the Calendar. That brought the total days of the Calendar to 354, aligning it with the more logical lunar year.

But there was a problem. Mr. Pythagoras and his followers were superstitious (yes, being a mathematician is no guarantee). They believed in luck associated with odd numbers. So they added one more day to make it 355 days and made sure that all months had either 29 or 31 days except for flexible February. That's how the tradition of adding days was born (and later will become hugely relevant with a leap year).

Julian Reforms

Julius Caesar was an incredible person. His 55 years of life were full of all the adventures possible for a human being. He was a victorious general of the Roman military. However, fate forced him to rebel against his nation. Ensued civil war, and Caesar became an unlikely king.

The problem with the Calendar at the time was, it was up to the Council to declare holidays, add days to the year, or decide the tenure of relevant governmental policies.

Oh, as we know about human nature, we cannot see others happy. Especially if they are trying to do something good for society. The Council's system of Calendar was highly manipulative, and they will continuously strive to use their power to create problems for Caesar. For example - they will announce a holiday on a day when the senate was about to vote on an important policy if they were not happy about it.

When Caesar was fighting a decisive battle in Brundisium, the Roman Calendar was running weeks ahead of its time. According to the Calendar, the winter has already passed. However, in reality, it was autumn, and Caesar had a tough job ahead of him to find supplies for his army.

Fed up of all these reasons, when Caesar came back from Egypt, he decided to adopt a better calendar that does not require constant modifications. He also decided to frame an automated system, which will bring the total number of days to 365 and follow the solar cycles. To align the next year's start date on January 1, he ordered several changes to the current year. The result was that the year 46 BC was 445 days long and earned the name 'Year of Confusion.' But all the years after were of the same length (till 1972 when two leap seconds were added for Coordinated Universal Time (UTC)).

When to hunt for Easter Eggs?

There was a significant flaw in the Julian calendar. It has a leap year every four years, which means 100 days were added over every 400 years. So the average length of the year was 365.25, whereas the period of an actual solar year is 365.24219879. The resulting error gave us an extra day every 130 years.

These extra days were not a significant problem for a civilian because the change was subtle and happened over generations. But for the 16th Century Church, it created a considerable challenge. You see, Church at that time was heavily dependent on Easter for the calculations of all the festivals and activities.

Most of the Church's feasts were tied to the position of Moon. If Easter keeps drifting, it will cause a lot of problems. It was a source of power for the Church, and changes to the routine like celebrations moving into summer are not suitable for the followers who still believed that Sun rotates around Earth.

So Pope Gregory XIII, after deliberating for 40 long years, decided to remove ten days from the year 1582, bringing the Easter of 1583 to March 10, which was their preferred date. That's how the current Calendar was named Gregorian Calendar, immortalizing the Pope forever.

They also changed the leap year rule to 97 days over 400 years as opposed to 100 where it stands currently. Remember the famous Y2K problem?


Book Summary

Anmol Mohan

I am just trying to make sense of this world. I am interested in the hardest puzzles like Consciousness, Humanity and Multiverse. Sharing my honest learning during this journey.