Today we celebrate Gioachino Rossini, born in Pesaro, Italy in 1792. By normal math, the famed opera composer and eccentric would be 224 years old today. But with Rossini it’s not so simple. Because he was born on February 29, i.e. leap day, we need to employ some special math to calculate his birthday. So today, instead of 224, we say that Rossini is 54.
But Chris! That math doesn’t add up! 224 years divided by 4 years doesn’t equal 54.
You’re right! It’s 56. Read on.
Leap years are not as simple as you may think. According to Eva Bodkin-Kowacki at the Christian Science Monitor this is how it works.
Contrary to what you’ve been told, one year is not 365 days long; it is 365.242159 days long. And so in order to accommodate this approximately quarter extra day each year, the Gregorian (and Julian) calendar adds one day every four years, February 29. That’s not all though. This is where the special math comes in.
Because one year is a little less than quarter day longer each year, every centennial year we skip leap day all together and have a normal year:
1792 = 366 days
1796 = 366 days
1800 = 365 days
1804 = 366 days
Since Rossini’s birthday in 1792, there have been three centennials: 1800, 1900, and 2000.
But Chris! 224 years divided by 4 years and then minus 3 centennial years still doesn’t equal 54.
Correct again! Read on.
The centennial thing isn’t a perfect fix for the 365.242159 day year either. It’s close, but not perfect. One more accommodation needs to be made: every centennial year that is divisible by 400 does not skip the leap day, and February 29 is added back in:
1800 = 365 days
1900 = 365 days
2000 = 366 days
2100 = 365 days
Since 2000 is divisible by 400, it is counted toward the total number of Rossini birthdays: 54.
LONG STORY SHORT
2016 minus 1792 = 224 years
224 divided by 4 = 56
224 minus 3 for the centennial years 1800, 1900, and 2000 = 53
Add one year back for 2000, a centennial year divisible by 400 = 54
And voila! Rossini is 54 years young today. Now, if your brain is steaming as much as mine was, then enjoy this to cool it off:
"Una voce poco fa" from Rossini's Barber of Seville with Kathleen Battle