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The Origin of Leap Year – A Scientific Context


Before we go into the history of the origin of the leap year deeply, here is an overview of the leap year that draws a context for our understanding. Everyone knows that a leap year comes after every four years, this is as basic as our understanding that the earth completes its axis around the sun in 365 days. However, this is not the exact time of completion; the earth completes its one complete rotation in 365.25 days. That is 6 more hours excess in a year of 365 days that do completely unnoticed by the general populace.

These 6 hours are calculated and compensated every 4 years that results in a leap year adding an extra day in February. So, in a leap year, the total time for the earth’s one complete rotation is 366 days.

The Greek astronomer Hipparchus discovered this 2000 years ago. His calculations have been perfect to keep the earth’s rotation completion aligned with weather conditions along with other schedules that are dependent on the earth’s complete rotation around the sun. He said that an accurate accumulation of the extra hours that we do not count individually in a year are calculated by adding just one day in a year.

A leap year keeps the flow of the calendars works smoothly and the weather condition are also dependent on it to a great degree.


Weather Seasons

The weather seasons are all decided by looking at the sun; also, the farming plans are based on weather prediction. It tells if it is reliable and appropriate to seed, crop, and harvest according to the seasons. Moreover, the sun’s movement is in the horizon direction and it moves towards the south during winter and to the north during the summer.

If we go in-depth with the seasons and do not add a day after every 4 years then this might result in a climate tragedy. The months would change their seasons with the earth’s rotation around the sun after 750 years’ time span.

It would become something like June might be having winters and November to have summers. Furthermore, the festive timing would differ due to the change in timing and weather; everything will go topsy-turvy.

Leap year also helps in keeping the schedule precise and helps in sticking to the scheduled plan. The leap year was established years ago. It has a long history, you would love to read about the leap year history dates back to the Stone Age.


History of Leap Year


If you see the calendar from different cultures that are Hebrew, Chinese, and Buddhist. They all use a lunar-solar calendar which tells the direction of the moon along with the position of Earth rotating around the sun. This shows that the moon is 11 days behind in contrast to Earth which is one day behind in a year.  

Furthermore, such calendars are required to add additional months or days in the existing months known as intercalary or interstitial months to be on track otherwise they have had lost the track of earth's complete rotation around the sun.

However, historians are still confused about certain things as how the Romans had kept track of the Earth’s rotation and how did they manage with them.  According to history, they have a year of 10 months and an undefined winter season. They didn’t know the length of the winter season.

Also, this is why they were not connected with the solar year system. With time, they added two new months which are January and February.  Although the problem remained unresolved. They also added an intercalary month of around 23 days known as Mercedonius.

Mercedonius was incorporated in the year to find the difference between them. The intercalary month is added in between February to lunar cycle reasons. But this thing made the matter more confusing and the roman year and solar year ended without any synchronization.

Ancient Time Taking Measuring Strategies

In ancient times, it was quite difficult to measure the time. The Egyptians used the lunar calendar to keep track of the time. The system of adding days in a year is an old strategy to maximize time pairing with the solar system.

According to Lowe, when Egyptians approached this theory and applied it, they knew they were mistaken somewhere and also added 5 additional days to celebrate their festivities.

How A Leap Year Is Born?

You must have heard the name of Julius Caesar, a Roman politician, and conquerer who invented the concept of a leap year in 45 B.C. He is the pioneer for giving the concept of the leap year.  In the early times, the roman had a fixed 355 days in a year which means the recurrence of the festivals they celebrate would be on the same date as before.

Also, a 22 or 23 days month was added after every second year to keep the occurrence of festivities on the same day as before. This calendar was also known as the Julian calendar.

The Great Caesar wanted to simplify things and adjusted the month with different addition of days in it making a year of 365 days. All the calculations were done by Caesar and his astronomer, Sosigenes.

The Julian calendar went for a good period until Gregory VIII that further implements the scientific logic to apply on the calendar making it more reasonable after the above calculations and changes around the world. By the time in 16th century in 1582, Pope Gregory VIII worked on the leap year concept to refine the calculations. So, he stated that a century can be a leap year if divisible by 400.

Besides, Gregory with his team formulated another calendar and synchronized it with an event and festive accordingly. He noticed that the Julian calendar is 11 days long which does not correlate with the present solar system calendar. So, they made a calendar that does not just run but also adjusts with the time. In a Gregory calendar, the day changes right after the clock strikes 12 o clock at night. Additionally, if a century is divisible by 400 then it would be a leap year. 

Acceptance of the Calendar

The calendar was accepted by the catholic states immediately. But Russia accepted it later after World War 1. The Gregorian calendar is now used by Saudi Arabia despite the fact that the Islamic calendar follows the lunar calendar.

Why Leap Day Is In February?

The month of February is not always this short. If we see the history, this month had 30 days back in the times of Romans. It was changed by Augustus Caesar, the nephew of Julius Caesar. He was not happy with the idea that a month named after his uncle's name has 31 days and his month of August does not have the same days as his month.

So he took 2 days from February and added them in August. He had also won some battles in August and this month was named after his name.

The Calculation of Leap Year

The calculation of leap year is not that problematic at all. You can simply calculate with the logic of applying that it would be a division of 4 or if in 1000’s then it would be divisible by 400. This way you can easily calculate the leap year. Here is the list of future leap years. Since 2000 was a leap year. So we know that it happens after every 4 years and is divisible by 4.

So it is easy to find out the leap years. Following are some leap years of the future includes the years 2024, 2028, 2032, 2036, 2040… and the list goes on.

The above calculation is based on the concept of the Gregorian calendar.

Importance of Leap Year

We must have a leap year after every 4 years.  Although we celebrate the New Year every year almost around 6 hours before the completion of the earth's rotation around the sun.

It does not seem a big deal at that time however it is a big deal if we see it in a long term. The effects of 6 hours approximately could have been seen if the Georgian calendar is not present today. The problem is so much that we are always one day behind the earth’s actual position around the sun. If we do not add one day in February, we might end up celebrating festivals like Christmas in July along with other events that would be celebrated in other months of the year.

The Gregorian calendar is the standard calendar that is used across the globe and keeps its flow with the solar system. Here is why the leap year is so important to be present! Thanks to Caesar and Pope Gregory VIII for their effective formulation of the calendar.

·      Gregorian calendar With the Best Track Result for Leap Year

The Gregorian calendar has the most logical collection for leap year. You can identify a leap year easily if it’s divisible by 4 and not 100 even for centuries the same theory is applied. Let’s take an example of leap years from the 2000s.  The leap year is 2004, 2008, 2012, 2016, and, 2020.

·      Leap Years Rules

The leap year is divisible by 100 as well but 1900 is not a leap year century. It must also be divided by 400. When the modified version of the calendar is formed. 10 days are dropped in October to compete with the solar system through the calendar.

As a result, there are some countries present in the world which does not have the dates when the Gregorian calendar came. Their history for those 10 days does not exist.

Gregorian calendar Modification for Future

Gregorian calendar is a good choice to take along like the rest of the world. However, it is not 100% accurate and requires working along with the earth’s position. There are still some changes which need to be done. It requires a lot of research to fix the infrequent errors. It would take around 3000 more years to recognize the minor variation in time to add to the calendar.

Apart from that, this system works in a way that is only a minute longer than the actual solar year time. The average period of the year is 365.2425 days to be exact. Astronomers are still working today to find something new and interesting!


Lastly, the Gregorian calendar is the only calendar that is being used as a standard all around the world. However, one cannot guarantee of it being accurate and perfect and by the revolution or orbital rotation with the sun. The leap year is an important factor in measuring a lot of things which includes the weather and plan certain schedules accordingly in the space technology system. If the Gregorian calendar was not developed we would not be able to calculate the accurate timing for certain weather conditions across the world. ­­­Leap year invention is mandatory for measuring and scheduling pre-requisites for certain things.

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