Leap Day

Today is leap day. But why is it added and how the system works? WKT, Earth completes a rotation (spins in its own axis) not exactly in 24 hours. Its exactly takes 23 hrs 56 mins 4secs. 3 mins 56 secs to exact 24! So, we're actually borrowing this 3 mins 56 secs from the real next day of the Earth and using it. Leap day is added every 4 years in the month of February as the 29th day of the month and 60th day of every leap year. So to find whether a year is leap or not, just testing the year for divisibility by 4 is enough. For example, considering the year 2020, when divided by 4 (2020/4=505), it leaves no reminder. In a year, 365 days, so, 365*3 mins 56 secs will give the math of the total extra time we borrowed. But in the actual scenario earth doesn't orbit (revolution) the sun in exactly 365 days. Considering all the math we've done and the reason, the real orbital time is less than 365 calendar days. That is, we're thin...