Today is 29 February, 2020! This year is a little different from other years, because this year February has not 28 days but 29! Anyway, everyone knows that much by now, but what they do not know is why this one extra day exists. So let's find out.
The way our years are counted is not arbitrary. There is a scientific basis to it. The Earth takes about 365 days to go once around the Sun. So 365 = 1 year. But there are some problems here.
In science books as children we all surely read that the Earth takes about 365 days 5 hours 48 minutes 47 seconds to go around the Sun. What happens to the extra 5 hours 48 minutes 47 seconds that gets dropped every year? So scientists adjusted for it by inventing this leap year method. How?
Since this extra 5 hours 48 minutes 47 seconds is close to 6 hours, if we take it as 6 hours then every 4 years gives 6×4 = 24 hours. Does the number look familiar? Yes, you have guessed right. It equals 1 day. So every 4 years one day is added. Since February is comparatively short, the day is added to this month, making it 29 days.
But a problem still remains. We took 5 hours 48 minutes 47 seconds as 6 hours. So are we not taking an extra 11 minutes 13 seconds every year? Then over 100 years the excess is 1122 minutes or 18 hours 42 minutes. Which is close to 24 hours or 1 day. As a result this extra day is dropped every 100 years. So after every 100 years there is no leap year.
But a gap remains even here. By taking 18 hours 42 minutes as 24 hours and cutting one day every 100 years we are committing quite a sin, because about 5 hours 18 minutes is left over. Now multiplying those 5 hours 18 minutes by 4 gives 21 hours 12 minutes. Now, since every 400 years this extra 21 hours 12 minutes again comes close to 24 hours, one extra leap day has to be taken again every 400 years.
Now you will say: that leaves 2 hours 48 minutes too many, doesn't it? Let it be, friend, let's not go any further. You understand — I am poor at arithmetic 😛 so if I keep calculating my head will give out this time round. I know the calculation has gone over many heads. So let's summarise a little.
1. Every 4 years one extra day is taken. This is called a leap year. Generally the years divisible by 4 are leap years. The next leap year is 2024. 2. Every 100 years one leap year is cancelled. Generally years divisible by 100 do not get a leap year. The year 2100 will not be a leap year. 3. Every 400 years one leap year is added back. Years divisible by 400 are leap years. The year 2400 will be a leap year.
That is all for today. If anything is unclear, let me know in the comments. Thank you for taking the trouble to read.
