You’re probably already aware that this month, February hath not 28 days but 29. It’s Leap Year! We typically say that it takes 365 days for Earth to travel all the way around the Sun, and that’s what our calendar generally shows. But in reality, it takes just a smidge longer: 365.2421 days.
That fraction of a day may seem negligible, and it would be, if it didn’t accumulate over time. But if we never adjusted the calendar, then over some years, we’d find our seasons didn’t align any longer. Eventually, those of us living in the Northern Hemisphere would be going to the beach in December and throwing snowballs in June.
Thousands of years ago, the ancient Egyptians realized that tracking the days in a year needed to be adjusted to keep up with the Sun. That culture depended on knowing its growing and harvest seasons with predictability. The Egyptians realized that there were 365 days, and then some, in a complete agricultural cycle. But they just added a day to their tracking when their astrologers noticed the stars were far enough out of alignment to need a correction. The extra day wasn’t regularly predicted.
Julius Caesar learned of the Egyptian process when he visited that country during his reign as Emperor of Rome. He incorporated the calendar adjustment into a revised Roman calendar and introduced the additional day every four years, almost like we know it now. This Julian Calendar went into effect in 46 B.C.
And it was almost right… but not quite. Did you know that Leap Year doesn’t actually happen every four years? If we added that leap day every four years, in time we would creep ahead instead of falling behind. To make up for the tiny fraction of a day missing (the difference between .25 days and .2421 days), we don’t leap ahead in new millennial years that are not divisible by 400. So, 2000 was a leap year, but 1900 was not.
Having a hard time visualizing all this? So were we. This graphic from planetary scientist Dr. James O’Donoghue might help. It shows what would happen to our seasons if we didn’t make that leap when we do.
Ask a parent if you may view the graphic in this link: https://twitter.com/physicsJ/status/1225386964049788928?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1225386964049788928&ref_url=https%3A%2F%2Fwww.loopinsight.com%2F
He made the Moon to mark the seasons; the Sun knows its time for setting. — Psalms 104: 19
(Dr. James O’Donoghue’s graphic shows what would happen if we omitted Leap Day adjustments. James O’Donoghue via Twitter)