The Story of Calendars

Remember the days when we used to source things in nature as a way to track time? Of course not. Or maybe you were a scout when you were still in grade school.

Today even the little ones want access to technology. But the fact still remains that days begin with the rising sun and end with it setting. The bright moon and stars light the sky in remote areas today.

Now imagine primitive man in the tropics. When the moon is full and big, it rises around sunset. Human curiosity and pursuit for logic must have led to counting days between the occurrences of these simultaneous events. That interval is still referred to as a lunar month.

Using this month, primitive man must have counted the lunar month interval between other annual natural events like spring or winter to get a lunar year.

However today we know that there are approximately 365 days in a year and the exact time between two full moons is short of 30 days. This creates a shortage of days year after year. The lunar calendar incorporated these days by introducing the concept of “intercalation” or addition of days or months to realign the calendar.

“Calendae” was the term for the first day of a month in the Roman calendar. The word derives from Proto-Indo-European *kelh₁- (“to call, shout”) so it must have been a practice to announce the start of a month in those days.


Quest for accuracy

The calendar as we know it today, is named after Pope Gregory XIII, who introduced it in October 1582. It was the result of a long quest for accuracy. The Romans originally had a ten-month calendar that was independent of the moon. The number of days varied from 29 to 31 and added intercalary months. By the time of Julius Caesar, the calendar had expanded to twelve months with months alternating between 31 and 30 days except for February which had 28 days except for leap years. The Gregorian calendar approximately 0.002% more accurate than the Julian calendar in the length of the calendar year. The claim is that this adjustment makes Easter fall closer to the actual day in biblical history.


Politics of accuracy

It can easily be inferred that this last change was clearly a case for political and religious control. Despite its introduction in 1582, the calendar took its time to get accepted throughout Europe especially with the growing presence of Protestant churches. Great Britain and its colonies did not adopt this calendar until 1752. Eastern European countries adopted it in the 20th century. . especially with the growing presence of Protestant churches. The Eastern Orthodox accepts the solar accept of this calendar but follows the Julian calendar for both Christmas and Easter.


Religions and calendars

It is obvious that Hindus, Buddhists, Muslims and Jews do not follow the Gregorian calendar for religious purposes.

Gregorian Calendar
Gregorian Calendar

In fact, they have their own unique versions of the lunar calendar. The most developed of the three is the Hindu and Buddhist calendar which is a lunisolar calendar as described in the introduction. Because their beliefs and practices do not require date accuracy – as in birth or death of a prophet – their calendars are very fluid. The religious practitioners are comfortable with festive days moving a few days here and there. The Jewish calendar adds intercalary days to adjust to the solar cycle. The Islamic calendar rejects the adjustments proposed in administering the Jewish calendar and eliminates any form of intercalary. This twelve-month lunar calendar cycle is always moving ahead by a 29-30 days every year.


Alternate calendars

The official calendar of Iran and Afghanistan is the Solar Hijri calendar. It begins on the vernal equinox in March with twelve months each corresponding to a zodiac sign. The first six months have 31 days, the next five have 30 days, and the last month has 29 days in usual years but 30 days in leap years.

Solar Hijri calendar
Solar Hijri Calendar

Well, that is how we follow a calendar of 12 months of pre-defined number of days that total usually to 365 days and 366 in leap years. Unfortunately neither number is divisible by seven, a long followed repeating cycle of days. This Greco-Roman concept was adopted across the world much earlier than solar calendar.


Time for thought?

Technological advances led to the accuracy of our current calendar. Will they eliminate its existence? Today we can purchase oranges in the middle of winter and even grow rice in the Arctic. Changing seasons have fewer consequences in out interconnected and global world. Computer systems measure time in microseconds.

Intervals between events are measured in microseconds. Today we are able to measure the sidereal day, time taken by the earth to rotate on its axis relative to the stars, and is almost four minutes shorter than the solar day because of the earth’s orbital motion, very accurately. When seen from that perspective, day, weeks, months and years are very arbitrary. They are simply our way to retrofitting tim to older constructs.

Time Trivia


The science of timekeeping is known as horology.


A nanosecond is one billionth of a second.


A picosecond is one trillionth or 0.000 000 000 001 of a second.


Planck time is the shortest known time span. It is the time it takes for light to travel a Planck length or 1.616199 × 10-35 meters in vacuum.


Easter is normally celebrated on the first Sunday after the first full moon that occurs on or after the Spring Equinox. So although the church follows a solar calendar, Easter Sunday is based on the lunar and the continuous seven-day cycle or weeks.


Note light year is not a unit of time but distance. The International Astronomical Union defines a light year as the distance light travels in vacuum in one Julian Year. In astronomy, a Julian Year corresponds to exactly 365.25 days.


A fortnight is a unit of time that refers to 14 days. It comes from an old English word, fēowertȳne niht, meaning fourteen night. It is commonly used in the UK, Ireland, and many commonwealth countries. People in the US and most parts of Canada use the term biweekly to refer to the time period of two weeks.


Judas Iscariot, the apostle who betrayed Jesus, has been labeled “the 13th guest” at the Last Supper. Its significance and human proclivity for superstition has led to widespread belief that the number 13 is unlucky. Any month in the calendar that begins on a Sunday will have a Friday, the 13th, and there is at least one Friday the 13th in every year. A single calendar year can have up to 3 Friday the 13ths.


Despite being larger than mainland United States in terms of land area, China has one single time zone (UTC+8). Mainland United States is divided into four time zones.


The Sun’s light reaches the surface of the Earth about 8 minutes after it has left the surface of the Sun. It takes 3 minutes to reach Mercury and about 4 hours to reach Neptune.


The Antarctica and the Arctic are the only areas where all standard time zones currently followed in the world, converge. Amundsen–Scott Station on the South Pole however uses New Zealand time.


Parth Upadhye

Parth Upadhye is an artist,
cook, designer and father

Visit Parth’s at

or view his artwork at


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