In my previous post I asked you an easy yet interesting question. This is the answer for it with an explanation. If you haven’t answered that question, go to this link without scrolling down to see the answer.
The answer to this question is No, it wasn’t.
Most of us know that a leap year is an year which consist one more day than a usual year and that a leap year comes after every four years. So accordingly, we also know that an year which is divisible by 4 is a leap year. Therefore, you may argue that 1900 is divisible by 4, so it must be a leap year but this is not so. Also you may say that since a leap year occurs every 4 years and 1896 was a leap year so 1900 must also be a leap year.
Lets try to understand this concept:
What is an year ?
The time taken by the earth to complete one revolution around the sun. Right ?
What is the duration of an year ?
It is 365.25 days. Right ?
No, slightly mistaken, 365.25 is a round-off for the actual time that is 365.2425 days.
For every 400 years
Number of days we calculate (using 365.25 days) = 365.25 x 400
= 146100 days
Actual number of days (using 365.2425 days) = 365.2425 x 400
= 146097 days
Difference = 146100 – 146097
= 3 days
So to reduce 3 days, three leap years must be made normal years. Now for example if these 400 years were from 1600 to 2000.
The 3 leap years to be made normal years were,
So in this way the time calculated by us now matches the actual time.
The conclusion we come to is that for an year to be leap year it should be divisible by 4. But if the year is divisible by 100 then it should also be divisible by 400 to be a leap year.