I am sure everyone has at least once witnessed a complex system which always seem to be a very simple one. We take these simple systems for granted and assume that this is how it must work. But digging deeper in the history we often find something which is amazing and shakes our entire understanding of the system. Gregorian calender system is one such system. How? Let’s find out…

An year, in very simple terms, can be said as that time period which Earth takes to complete one full revolution around the Sun. We found that one year is around 365 and one-fourth days. To adjust this one fourth day, we added one full day to every fourth year. This was the basis of Julian calender system which existed before 1752.

But to be precise one year is 365.2424 days. So whenever we were celebrating the new year day, Earth covered a little more path in it’s elliptical path, than one complete revolution. This small change accumulates and becomes a difference of 11 days in about 1600 years.

What the difference of 11 days means? It means whatever the Earth’s position is it today, it will be ahead of it by 11 days in about full 1600 years.

Now this lead to some discrepancy among various religions when to celebrate their occasions as some followed moon’s cycle.

In order to correct this and save future trouble some decisions were made in year 1752. If you are hearing them for the first time, you’ll be amazed to know it. They are as follows:

  1. Pope said in a stern voice (I am being dramatic here)- “Erase these eleven days as we are already ahead according to the time of year”. And hence eleven days from September month of year 1752 were erased. Dates from 3rd September to 13th September 1752 don’t exist. Surprised? It’s true.

  2. Pope also said that from now on only those years will be leap years who are divisible by 4 or by 400. Century years that are divisible by 100 but not by 400 will not be leap years.

I think pope was a mathematician or he had an advisor who was good in mathematics. I say this because giving this rule of calculating leap years ensured that we will not fall into the same trouble in future again.

How? Let’s see…

According to rule 2 above, calculate how many days there will be in 400 years.

(Thought process….

Hmmm, in 400 years there will be 100 leap years according to old definition, but then I have to cancel those century years which are not divisible by 400, there are 3 such century years in a range of 400 years. So volla, in 400 years number of leap years are- 97 LEAP YEARS. )

Total days in 400 years (According to calender) = 400*365 + 97 = 146097 days.

Now we know that one year consists of 365.2424 days. How many days in 400 years?

Total days in 400 years (According to observation)= 400*365.2424 = 146096.96 days.

It comes almost same with a difference of 0.04 day in 400 years. That’s bearable. And hence the law was signed to bring the rules in effect immediately.

I know, this sounds bizarre right? But this is how it is.

If you still have some doubts, read this:

There is a cal command in linux systems which gives calender of years in range 1 to 9999.

Check for year 100. You will find it as a leap year because the new rule was implemented in 1752.

Need something more? Check calender of year 1752 and look for September month. You’ll find 11 days missing.

Also to support what I have said, calculate this:

We got the difference of 0.04 days in 400 years. In how many years will this difference be of one full day?

Years for difference of 1 day = 400/0.04 = 10,000 years. And that is the range of cal command because it hasn’t been decided where to put this one more extra day.

Be force with you!!!!