Different Calendar Types and their History

About time

Here we are, in the year 2019 and we still can’t find a fulfilling definition of what time actually is. We can
definitely, feel the pass of it but we can only agree to say that it’s ever going and seemingly irreversible
a succession of events through existence.

So maybe we are not able to tell exactly what time is, but for sure we can measure it just by taking into
account the time spent between two different and not simultaneous events.

About calendars

The easiest way to do this among prehistoric men was probably the time between two sunrises or two
sunsets, and that’s what we call now “a day”. Or the time between two comings of winters, and that’s what
we call “a year”

So after we became aware of time and its pass, and developed new ways to measure and divide it, we
realized that we needed a system to organize our daily activities not only for one day but for many at a time.
And that’s when we created our first calendars.
So, calendars are basically a matter of convenience.

Convenience to whom?

To the society that decides to use it, right?
As you can imagine, in an ancient world where every citizen was basically on their own, many different
societies adopted different calendars.

And through many centuries, these calendars were refined and tuned up until we got the one is used today.
But wasn’t until recently that most of the world decided to agree in the simple fact of giving the same answer
to the old, classic question made for any unaware time traveller, we might bump into: “what year is this?”
So next, we are going to talk about some of the ancient calendars that were and are still relevant because of
their popularity, longevity or accuracy.

Prehistoric calendars

Several ceramic artefacts found in archaeological excavations are believed to be some of the oldest forms of
calendars made by men.
Also, some of the most notorious megalithic structures build as far back in the Neolithic period were arranged
with timekeeping purposes.

Antiquity and Middle Ages

During this period, and with the discovery of the mathematical principles that allowed to do astronomical
calculations, different civilizations set the basis to what modern calendars are today.

But first, we saw many solar (based on the seasonal changes synchronized with the motion of the Sun, as
the Persian calendar), lunar (based on the phases of the moon, as the Sumerian calendar) and lunisolar (a
combination of both, as the Hindu calendar and the Chinese traditional calendar).

Some Mesoamericans cultures used a double calendar, a 260-days year calendar for sacred activities, and a
365-days year calendar for usual activities. The latter being surprisingly close to modern calendars.
Although been far away from being as accurate as today’s calendars, the old Roman calendar (with years
being only 304 days and 10 months long), was the base for today’s calendar, giving its name to our current
months from March to December (January and February were added later).

Julian calendar

A radical modification to the old Roman calendar made by Julius Caesar in 46 BC, that would serve as the
predominant calendar in the Roman empire, most of Europe and in the Americas (conquered by Christian
Europeans) for more than 6 centuries.

Many years after the introduction of the 11th and 12th months of the year, the Julian calendar would establish
the now familiar 365-days year to the Roman empire, with a leap 366-days years every 4 years due to the
adjustment needed because of the 365.25 days length of the year.
It would be the basis for the current Gregorian calendar.

Gregorian calendar

The most used calendar in the world. And only a minor reform made to the old Julian calendar (which is still
used by some churches around the world) approved by Pope Gregory XIII in 1582 (although, there were claims
to change the calendar as early as the 8th century).

The reason for this change was that the actual year length was not 365.25 days, but 365.2425 days. This little
reason made that the canonical day of Easter, which was supposed to concur with the spring equinox, and
the actual spring equinox was in an increasing divergence.

The practical way to fix this was to make that year divisible by 100 would only be leap years in case they
were divisible by 400, and the deletion of 10 days (from October 5th to October 14th) from the calendar of
the year 1582.

Note: all citations made on this article were done using the Vancouver system and a Vancouver referencegenerator

For further information, feel free to watch:
A Brief History of the Calendar and Time Keeping

The Leap Year as Explained by Neil deGrasse Tyson | StarTalk

Paul Davies. About Time: Einstein’s Unfinished Revolution: Simon & Schuster; 1996.

The structure basics of the Jewish calendar

Introduction The Jewish calendar is lunisolar meaning that it is based on the movements of the moon and the sun. Essentially, the earth completes a full rotation on its axis in one day, the moon goes around the earth in one month (about 29 days ), and the earth circles the sun in a year (365¼ days or 12.4 lunar months). This calendar works by factoring these three elements.


The Jewish calendar consists of 12 alternating months with either 29 or 30 days each with a total of 353, 354 or 355 days in a year. An average lunar year is 354 days. It is adjusted to the solar year which has 365¼ days through the introduction of leap years to ensure that all major festivals coincide with their respective seasons.


In this calendar, each day starts at sundown the day before and ends at sunset the following day. This has its origin from the Bible which states that God created light since the earth was in darkness. He called the light day, and the darkness night. Thus, every day is recorded this way with every light and darkness interval being marked as one day. Each week has seven days.

Similar to the American calendar, the first day is Sunday, and the last (Shabbat) is Saturday. There are restrictions as to which days certain holidays should fall. Such holidays include Rosh Hashana, Yom Kippur, and Sukkot. For instance, Yom Kippur should not come next to Sabbat. To avoid this, a day is either added to the month of Marcheshvan or subtracted from Kislev.


The month of Nisan is the first month of the calendar while Tishri, the seventh month, is when the Jewish New Year or Rosh Hashanah is celebrated. This concept of the year beginning at a different time from the calendar year is also seen in the example of a fiscal year as used by many companies. This calendar uses lunar months that begin with the first sliver of the new moon and can either last for 29 or 30 days.

Each year has either 12 or 13 such months. A year with 12 months is shorter than a solar year by 11 days. In this scenario, holidays come 11 days earlier every successive year. If left like this, these holidays would continue appearing earlier and pass every season. To counteract this, every few years a 13th month is introduced. A 13-month year is longer than a solar year by 19 days and is called a leap year.