28 Facts About Calendar: See How We Came Up With The Idea Of Dates

Anusuya Mukherjee
Jan 23, 2024 By Anusuya Mukherjee
Originally Published on Mar 22, 2022
Amazing Calendar Facts that you probably have not read before.
Age: 3-18
Read time: 7.6 Min

A calendar is a dating system that is used all over the world to keep track of days, weeks, months, and years.

During the ancient days, the course of the moon and sun were used for timekeeping. Gradually these techniques were optimized to create a more systematic tool called Calendar.

The term 'Calendar' is taken from the Latin word 'Kalendae' or 'Calendae,' which refers to the first day of the month according to the Roman calendar. It was the Sumerians who designed the first calendar during the Bronze age. However, over the years, calendars have changed, from Roman to Julian to Gregorian calendar. Each replaced one another with better accuracy. The day, month, and year are followed by many systems such as the Gregorian calendar, Islamic calendar, Hebrew calendar, and solar Hijri calendar. However, cycles can be coordinated with periodic phenomenons such as the Solar calendar, Lundar calendar, and Isolunar calendar.


The system of keeping track of time, day, month, and the year has been deeply rooted within different civilizations and cultures. Therefore archaeologists have strived towards tracing the timeline of the calendar that goes back to the neolithic age. The common units that were used by the historical communities were the day, the solar year or the tropical year, and the lunation.

The earliest calendar that is acknowledged is the Sumerian calendar which was followed by the Egyptian calendar, Assyrian calendar, and Elamite calendar.

Numerous calendars belonging to the ancient near East in the iron age appearing in the archaeological records were founded on Babylonian and Assyrian calendars such as the Zorastrian and Hebrew calendars.

The Roman calendar is contemplated to be founded on April 21, 753 BC.

Julius Ceaser later reformed the Roman calendar as the Julian calendar during 45 BC.

Pope Gregory XIII introduced the Gregorian calendar. The Gregorian calendar was primarily introduced as a betterment of the Julian calendar in 1582.

The Julian calendar was used in England till 1752 as most countries in Europe, particularly the Catholic countries, had already upgraded to the Gregorian calendar.

Since its introduction, the Gregorian calendar is being followed in most parts of the world.


Atomic Time

An Atomic clock, unlike other clocks, has its mechanism that is founded on light or microwaves with particular atoms in their excited state. It primarily estimates the electromagnetic signal of the electrons when they alter their energy levels. In the old days, however, early atomic time scales comprised a Quartz clock with its frequencies measured by a sole atomic clock. This Atomic time is a timescale developed by the atomic clock. It is more precise than the previously used astronomical means that involved Earth’s rotation and revolution.

The International Atomic Time (TAI) is founded on a system that consists of 270 laboratory-created Atomic clocks.

The signal from these clocks is further transmitted to the IBMW in Paris to form the TAI.

Leap seconds have been incorporated in the TAI timescale to generate Coordinated Universal Time which is closely linked to the actual timescale o Earth.

Currently, the cesium fountain clock provides the SI seconds to a remarkable level of precision.

The length of the year has been increased due to the slowing down of vernal equinox year, which is because Earth’s rotation has also slowed down.

Gregorian Calendar

The Gregorian Calendar was introduced in 1582 by Pope Gregory XIII and is widely used all over the world. It is also referred to as the New Style calendar. In 45 BCE, Julius Caeser added a leap day with another additional ten days to the Roman year.

The Gregorian calendar was accepted by Japan in 1873, while the Gregorian calendar was adopted by Russia in 1917.

The Gregorian calendar contradicts the solar year by 26 seconds each year.

Sweden once tried to exclude leap days for 40 years by developing February 30 after they swapped Julian Calendar with the Gregorian calendar. However, it did not work out.

The Gregorian calendar obeyed the rule of the Babylonian calendar, which has seven days in a week. Out of which, six days were founded on the phases of the moon, while the last day of the week was for a new moon phase or holy day.


Origin Of Names Of Month

The months of the Julian calendar, however, continued in the Gregorian calendar. The origin of the names of the month is based on Roman gods, Latin terms, and historical figures.

January is named after Janus, the Roman god, he possessed two faces that enabled him to see both past and present.

February is named after Februa, which is an ancient festival of purification of the Roman.

March is named after the Roman god of war, Mars. March is the commencement of the Roman Calendar.

Nevertheless, April is derived from a Latin term 'aperire' that implies to open.

While May is named after Maia, the Greek goddess, June is named after Juno, the Roman goddess of childbirth and marriage.

July and August refer to the two fundamental Roman emperors, Julius and Augustus. However, before these two months were labeled as July and August, they were called Quintilis and Sextilis.

September, October, November, and December are designated as the Roman numbers seven, eight, nine, ten as initially, they were in the Roman calendar.

Calendar is an important invention of mankind.

Did You Know...

You may know various facts about the calendar, but did you know these amazing facts?

The ancient Roman calendar was the predecessor of the contemporary Roman Calendar.

The actual Roman calendar is assumed to be created by the first Roman King and contained 10 months as it began with March.

The Chinese calendar is said to be invented by Emperor Huangdi in 2637 B.C.E

The years of the Chinese calendar are designated after Zodiac animals, and the traditional Chinese calendar is known as the lunisolar calendar, which is a lunar calendar.

The Muslim Calendar is also a Lunar Calendar, and the month comprises 29 to 30 days.


Q: Did you know facts about the calendar?

A: Here are some interesting facts about the calendar:

The leap day is required in the Gregorian calendar, and this is why an extra day is added in February after every four years so that the calendar can sync with the tropical year.

The Mayans used three calendars, out of which one was established upon the movements of Venus, which have 260 days. This was added with a solar year period to create a reoccurring period of 52 years called ‘Calendar Round,’ which is analogous to the century.

The credit of inferring Solar year goes to the Egyptians as they even approved a calendar that comprised of an extra day that would pressure after four years. It is assumed that Ceasar was introduced to this idea after Cleopatra conveyed the system to him.

Although the Jewish calendar follows the lunar cycle yet, it is still in synchronization with the seasons.

The Persian calendar or Iranian calendar is not rule-based, but it is based on observation and is more accurate than the Gregorian calendar.

In the early Chinese year, days were added with the lunar year to keep it in a similar position with the seasons.

The most commonly used pre-modern calendar was the lunisolar calendar, that adds sometimes incorporated one intercalary month to stay in sync with the solar year.


Q: When did the calendar start?

A: The first-ever calendar was used by the Sumerians in Mesopotamia during the bronze age. According to the calendar, every month is constituted of 29 or 30 days based on the moon.

Q: What is the Gregorian calendar?

The Gregorian calendar was authorized by St. Pope Gregory XIII. This calendar is fundamentally a solar dating system that is widely accepted and used. It replaced the existing Julian calendar.

Q: Who invented the Gregorian calendar?

Pope Gregory proclaimed the Gregorian calendar, however, it was not invented by him. Pope Gregory commissioned Christoph Kleu, the Jesuit astronomer and mathematician, to correct the previously followed Julian calendar.

Q: What purpose does the Gregorian calendar serve?

The purpose of the Gregorian calendar was to accurately estimate the date of Easter.

Q: What is the difference between Gregorian and Julian calendars?

A: The primary difference between the Gregorian calendar and Julian calendar is the number of average days, which is 365.2425 days and 365.25 days, respectively.

Q: What happened to the calendar in 1582?

A: The inaccuracy of the Julian calendar was put to stop in 1582 as Pope Gregory XIII called for the removal of 10 days in October. He removed the days from October 5 to October 14 and formulated an unusual month.

Q: Who started the calendar?

A: The Sumerians of Mesopotamia were the first to start the calendar, according to studies.

Q: When did we start counting years?

A: Dionysius Exiguus, a monk, devised the Anno Domini system in 525 to count years in his Easter table. Since then, these terms anno Domini and before Christ was employed in both the Julian calendar as well as the Gregorian calendar for counting years.

Q: Who invented the seven days of the week?

A: Emperor Constantine founded the seven-day week where Sunday was designated as the first day in the Roman calendar.

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Written by Anusuya Mukherjee

Bachelor of Arts and Law specializing in Political Science and Intellectual Property Rights

Anusuya Mukherjee picture

Anusuya MukherjeeBachelor of Arts and Law specializing in Political Science and Intellectual Property Rights

With a wealth of international experience spanning Europe, Africa, North America, and the Middle East, Anusuya brings a unique perspective to her work as a Content Assistant and Content Updating Coordinator. She holds a law degree from India and has practiced law in India and Kuwait. Anusuya is a fan of rap music and enjoys a good cup of coffee in her free time. Currently, she is working on her novel, "Mr. Ivory Merchant".

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