(Almost) once in four years

       
Today is February 29. I feel compelled to post something on this once every four years occasion. As I searched around, I realized I was actually wrong about this four years thing. I always thought as long as the year is evenly divisible by 4, it’s a leap year. But actually in order to compensate the 365.256363004-day revolution duration (not exactly 365.25), when the year is evenly divisible by 100, it doesn’t count as leap year. What about 2000? There was February 29 that year! Right, there is an exception of this “100 exception”: when the year is evenly divisible by 400, it’s a leap year again. So 1600, 2000, 2400 are leap years, but 1700, 1800, 1900, 2100 are not. (Oh my...)

Some people say leap days should be holidays because our annual salary is based on a 365-day year. If we work 366 days, it’s like working a whole day for free. I think it makes perfect sense.