As humans, we base everything on time. Seconds, minutes, hours, days, months, and years have governed our lives since time immemorial. It may not be widely known that there are several calendars worldwide, based on lunar, solar, and lunisolar cycles with differing years and New Year dates. Historical experts estimate that there are as many as 40 calendars worldwide!

The most public calendars are the Gregorian and Julian, Islamic, and Chinese calendars. We will explore these famous calendars of the world that contribute to the historical narrative of our time on Earth. Read on to learn more about why and how the calendars of the world came to be.

Julian calendar
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The Gregorian and Julian Calendars


Following the Gregorian calendar puts us in the year 2020. New years are celebrated on this calendar on January 1 each year, instead of as in the Julian calendar whenever Roman consuls entered office. In 46 B.C. Emperor Julius Caesar with the help of Greek philosophers and mathematicians, introduced the Julian calendar. There were three beginning dates in the Julian calendar:

• January 1
• March 1
• May 1

This calendar had one leap year and three standard years, hence an average year of 365.25 days per year. After every 128 years, the Julian calendar gained a day, and this lead to Pope Gregory XIII correcting the error with the Gregorian calendar in 1582, which replaced the Julian calendar.

Both these calendars are Roman, and solar because their dates follow the Earth's position as it revolves around the sun. The first countries to adopt the Gregorian calendar were Italy, Spain, Poland, and Portugal. Eastern Orthodox countries were hesitant to adopt this calendar because they thought it was a plot by the Roman Catholics to usurp them. All in all, it took 300 years for countries to adapt to the Gregorian calendar, with the United States eventually adopting it in 1753.

What makes the Gregorian calendar preeminent is that it is the calendar most widely used around the globe for administrative purposes. It features 12 months, seven days of the week, 365 days for typical years, and 366 days for leap years.

Eleven of the months in this calendar have 30 or 31 days, except for February, which has 28 days in a typical year and 29 days in a leap year. In this calendar, leap years occur every four years.

Both the Gregorian and Julian calendars have equal months and month lengths. However, in the Gregorian calendar, the years divisible by 100 are not leap years, and years divisible by 400 remain leap years. Thus, the Julian calendar will always remain 13 days behind the Gregorian calendar from March 1900 until February 2100.

Notably, most Eastern Orthodox churches still use the Julian calendar to calculate important feast dates like Easter. Some Orthodox churches use the revised version of the Julian to observe fixed feasts, while others utilize it for all administrative purposes. Interestingly, the Berber people from North Africa still use the Julian calendar.

Jewish calendar
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The Jewish Calendar


The Jewish or Hebrew calendar, like the Chinese calendar, merges solar and lunar cycles where lunar months consist of 29 or 30 days. Every 3 or 4 years, an extra 30 days are added to the calendar to sync it to the solar cycle. The Hebrew calendar is the official calendar of Israel and is used mainly by Jews for religious references. Lunisolar calendars like the Jewish and the Chinese calendars use months to estimate the tropical year. In the Jewish calendar, each month begins on the first day of the new moon. This history is based on:

• The Talmudic period: - This period began around 500 BCE and is based on “observation and reckoning."
• The Post-Talmudic period: - The Post-Talmudic period happened between 690 BCE and the 11th century C.E., basing it "entirely upon a reckoning."
• The Biblical period: - according to Bible History Online, it was during this time that Jacob entered Egypt, and Abraham was called to enter Canaan. Hence, the calendar is based upon "the observation of the sun and the moon."

The history of the Jewish calendar is based on biblical laws. In the book of Genesis, the modern Jewish calendar counts as Anno mundi, or the years since the world was created.

Notably, while many Jews outside of Israel use the Gregorian calendar, they do not use the abbreviations A.D. and B.C. A.D., Anno Domini means “the year of our Lord.” Because Jews do not believe in Jesus, they instead use the abbreviations B.C.E. - Before the Common Era, and C.E. – Common or Christian Era when denoting dates.



islamic calendar
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Islamic Calendar


Also known as the Hijri calendar, the Islamic calendar is popularly used by Islam to observe religious dates and events. It began in AD 622 when the Prophet Muhammad migrated to Medina from Mecca.

The Hijri calendar is different from the Western calendar and is highly regarded in Islam. The current Islamic year is 1442 AH, and within the Gregorian calendar, 1442 AH runs from August 2020 until July 2021.

The first day of the year on this calendar is the first day of Muharram - the Islamic calendar’s first month. It is a lunar calendar containing 12 months based on the moon's motion, with either 354 days or 355 days. A day within the Islamic calendar begins at sunset.

In 639 CE, Caliph Umar implemented the Muslim Calendar, counting it from the lunar month. Each lunar month begins when the lunar crescent appears after a new moon. This cycle has resulted in the Islamic year being 11-12 days shorter than the Gregorian year. Therefore, the Islamic New Year doesn’t occur on the same day of the Gregorian New Year, and the first day of the week corresponds to the Sunday of the planetary week.

All Islamic historical occurrences and celebrations are included in the Hijri calendar. These include:

• Al-Hijra - The Islamic New Year, which marks the end of the Prophet Mohammad's journey from Mecca to Medina.
• Ashura - A major religious commemoration of Hussein's martyrdom, the Prophet Muhammad's grandson, at Karbala
• The celebration of the birth of the Prophet Muhammad
• Eid ul-Adha - The festival of sacrifice
• Ramadan - The Muslim month of fasting
• Eid ul-Fitr - The end of Ramadan

Countries like Saudi Arabia primarily use the Islamic calendar in their every day lives. However, some Muslim countries prefer to use the Gregorian calendar for international civil reasons and the Islamic calendar solely for religious purposes.



Chinese calendar
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The Chinese Calendar


The Chinese or Agriculture calendar, like the Jewish calendar, is lunisolar. The years match the tropical year and the months correspond with the synodic months.

This calendar comprises 12 months of 29 or 30 days calculated according to the moon's cycle. The Chinese calendar was created from studying the moon's movements around the Earth, and it plays an essential role in Chinese agricultural beliefs.

The Chinese use the Gregorian calendar for non-religious purposes and the Chinese calendar to determine essential festivals. A typical Chinese year has 12 months and 353, 354, and 355 days. However, a Chinese leap year features 13 months, with 383, 384, and 385 days.

To determine a Chinese leap year, you’ll need to calculate the number of new moons within 11th months of one year and the 11th month of the next year. The Chinese name their years according to zodiac animal totems; 2020 is aptly named the Year of the Rat.



Final Thoughts


Other notable calendars of the world include the Persian calendar, currently used officially in Afghanistan and Iran. It is one of the world's most accurate calendars, dating back to the Prophet Muhammad’s Hegira in 622 CE. Unlike the Gregorian calendar, this calendar uses set mathematical rules to determine when leap years fall, according to the number of days between the two vernal equinoxes.

Another honorable mention is the Ethiopian calendar. This calendar is based on alternate calculations of the announcement of the birth of Jesus Christ’s, putting the Ethiopian calendar seven years behind the Gregorian calendar. In this calendar, it will be 2012 on September 11, 2020.

Although many calendars are recognized worldwide today, it is widely agreed that the most significant and most widely used calendar is the Gregorian calendar, which has been in existence since 1582. This trend is evidenced by the fact that the Islamic, Jewish, and Chinese and other communities worldwide use their calendars to mark religious obligations, festivals, celebrations, and other important dates, but still, use the Gregorian calendar for all civil and administrative purposes.