Why does February has 29 days every 4 years ?
Or why do we have a leap year ?
Or there are 365 day is a calendar and every 4 years there are 366 days ?
There are various question but each question has the same answer.
The very first thing you need to understand is, We consider day when the sun rises, and night after the sun sets or the moon rises.
The calculation of our clock is based on the movement of the earth which is rotating on its own axis, The Earth completes its circular motion within 24 hours.
Eg if the sun rises at 7 in the morning then the next day the sun will rise at 7 in the morning, on time. But this will never stay constant because the Earth while rotating in a circular motion around its own axis also rotates around the sun, Thus every few days we see a change in time of the sun rise and sun set. This also leads to change in climatic conditions.
Now the rotation of the earth around the sun is the reason of calculating the years, Which means how many rotations have we completed. Same example is our age If we are born in January 1956 then we complete the cycle of 12 months and again in January 1957 we can say that we have completed 1 year of our life cycle.
Now with the exact calculation of hours and days the earth takes around 365 day,5 Hours, 48 Minutes, 46 seconds.
Every year we leave 5 hours 48 mints and 46 seconds aside calculating 365 days a year, At the end of 4 year the sum of this hours will make a total of : 23 hours 15 mints 14 seconds which is almost a day. So at the end of ever 4 years we had to add up a day.
Thus there are 366 days in a year every 4 years.
Additional Questions :
There is difference of 45 mints 46 sec every 4 years, What about that.
To calculate that we have made a table :
| No of cycles of 4 years | Hours | Minutes | Seconds |
| 1 | 0 | 45 | 46 |
| 2 | 1 | 31 | 32 |
| 3 | 2 | 16 | 18 |
| 4 | 3 | 2 | 4 |
| 5 | 3 | 47 | 50 |
| 6 | 4 | 33 | 36 |
| 7 | 5 | 19 | 22 |
| 8 | 6 | 5 | 8 |
| 9 | 6 | 50 | 54 |
| 10 | 7 | 36 | 40 |
| 16 | 12 | 11 | 16 |
| 32 | 24 | 22 | 32 |
Now when we complete 32 Cycles of 4 years we get the difference added up together to bring a total of 24 hours 22 mints and 32 sec.
Thus first every 4 years we add 1 day, But every 128 years we deduct 1 Day coz we are getting a difference of 45 mints and 46 seconds Negative . ( still we leave a difference of 22 minutes and 32 seconds which is positive time)
In the Similar way when we calculate the difference
| No of cycles of 4 years | Hours | Minutes | Seconds |
| 1 | 0 | 22 | 32 |
| 2 | 0 | 45 | 04 |
| 3 | 1 | 07 | 36 |
| 4 | 1 | 30 | 08 |
| 5 | 1 | 52 | 40 |
| 6 | 2 | 15 | 12 |
| 7 | 2 | 37 | 44 |
| 8 | 3 | 0 | 16 |
| 9 | 3 | 22 | 48 |
| 10 | 3 | 45 | 20 |
| 64 | 24 | 02 | 08 |
Now when we complete 64 cycles of 128 years we get the difference added up together to bring a total of 24 hours 02 minutes and 08 seconds.
Thus Every 128 years we deduct 1 day, But we also have to add 1 day after every 8192 years.
Now we calculate like this every 8192 years
1) We add 2048 days to the calendar because of leap year.
2) We will deduct 64 days Because of the difference of previous 45 mints 46 seconds (Negative), Still we leave a difference of 22 mints & 32 seconds (positive).
3) We Add 1 day every 8192 years because of the difference of 22 minutes & 32 seconds (Positive), Still we leave a difference of 2 mints & 08 seconds
Thus to make is more simple, we can calculate 2048 – 64 +1
Which leave us to 1958, We need to add 1958 days every 8192 years.
Thus Every 4.15 years you can add 1 day at the base level, Still we will leave a difference of 2 mints and 8 seconds at the end of every 8192 years.
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