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Today one of my student has its birthday. So he brought a cake 🎂 along with candies 🍬 and chocolates 🍫 to school. We wished him happy birthday and he then distributed the candies and chocolates to the class. Then students asked me about my birthday and I told them that I was born on 14th of August 1995. They were planning to celebrate my birthday but I ask them to keep it simple. Anyways, one of them stood up and said, "Sir I celebrate my birthday once in every 4 years." My subconscious made me say "oh k, so you were born on 29th of February. Right?"
Yes sir, I am one of those unlucky kids who born on 29th February. He said sadly. Why you saying yourself unlucky? I asked. My all friends get gifts every year while I only get once in every 4 years. He went on, why we have leap year? Why we have to add one extra day every 4 years. I didn't know the answer as I never thought about it. Although at that time, I made him speechless by saying that "you are special. You are one of a very few people in the world who born on 29th February". But deep inside, this question made me curious about leap years. I talked to different persons, read tons of articles and watched videos but no one satisfies me about the topic. But I gathered some information from different places and now putting it here in simple terms. So here we go.
A leap year is a year that contains an extra day to keep the calendar year synchronized with the astronomical year or seasonal year. Every year whose number is dividable by 4 is called leap year. For example, 2016, 2020 and next will be 2024.
To know the reason behind the leap year, first let's know what Year is. A year is the time period in which Earth completes it 1 circulation around the Sun. Earth takes approximately 265 days to complete 1 circulation around the sun.
Let's focus on the word approximately. I said it takes approximately 365 days to complete a year. But if we look into details it actually takes approximately 365 days 6 hours. Although this 6 hours are negligible but after every 4 years it becomes 24 hours. 6+6+6+6=24 hours. Which is equal to 1 day. That's the reason we add 1 day extra after every 4 years to keep year in its specific order.
Let's say we don't want to add extra day every 4 years. Then in just 200 years, these extra days will combine to make it "2 months" which is too much. And we will not see the weathers in same days as we see now. As we see Winter during November to February now, then by not adding extra day every 4 years, we will see a huge difference in months of Winter. We may see Winter during August to November. So it was important to add an extra day to avoid these weather problems.
1692 was a leap year, 1696 was a leap year, guess what was the next leap year? 1700, Right? No, it was not. Similarly 1792 was a leap year, 1796 was a leap year but 1800 was not a leap year. Now as 1700 and 1800 were not leap years, what about 1900 and 2000 ? They were too not leap years, Right? No you are wrong again. Although 1900 was not a leap year but 2000 was a leap year. Didn't understand? Let me explain.
Remember I said focus on the word approximately? Earlier, I said Earth takes approximately 365 days 6 hours to complete 1 year. Actually it was not accurate again. It takes 365 days 5 hours 48 minutes 45 seconds to complete 1 year. Which means it is less than 6 hours by 11 minutes 15 seconds.
Although this 11 minutes 15 seconds are negligible but after every 4 years adding a day, our theoretical calander exceeds original time period of earth by 45 minutes. And after 100 years this 45 minutes combine to make approximately 18 hours. So by adding one day after 4 years, our theoretical calander exceeds 18 hours by original time period. That's why we have to remove at least 1 leap year after every 100 years. That's the reason why 1700, 1800 and 1900 were not the leap years.
But again although we exceed 18 hours then why we remove a whole day (24 hours) after every 100 years? Which means we again left behind by (24-18=06) 6 hours in compared to original time period. And again we don't have remove a day after 400 years to fix these 6 hours. (6×4=24). That's the reason why 1600 and 2000 were leap years.
And that's it for today guys. I know this is so confusing and boring. But if you really want to know why we have leap year then read this article again.
And If you find it boring then there are some interesting articles of mine, you would love reading.