Our theme for the month of October is “This Day in History.”

On October 15, 1582, Pope Gregory XIII decided that today—a day over four centuries later—would also be an October 15.

For centuries before 1582, the Roman Catholic church (and much of the Western world) had followed a version of the Julian calendar, the system named for and developed by Julius Caesar. But because of a calculation error, Mr. Ides of March’s calendar was drifting farther and farther from dates like the vernal equinox and winter solstice. The years were becoming longer and longer, and the days were becoming less and less aligned with the seasons.

Aloysus Lilius might not have received the naming credit for the Gregorian system, but in sixteenth-century Italy, he was the man with the plan to fix the calendar. His target? Leap years. Every four years, the Julian calendar had included these years with an extra day. But Lilius argued that—like many a high school geometry student—Julius Caesar hadn’t written down the correct formula. Yes, leap years should be observed every four years. But not if the year is also divisible by 100. If that year is divisible by 400 as well as 100, the leap year should be observed regardless.

All this sounds rather fussy to my twenty-first century ears. But imagine the kind of frustration a faulty calendar would have caused. For those like Pope Gregory, in charge of setting dates like Easter (the first Sunday after the full Moon on or after the spring equinox), a season and date misalignment would be confusing—at best. So, on October 15, 1582, Pope Gregory XII released a papal bull naming Aloysus Lilius’s system as the new standard.

Today, the Gregorian calendar is also known as the Western calendar (because most of the Western world uses it) and the Christian calendar (because most Christian churches use it). But even in those circles, Gregorian calendar adoption wasn’t immediate.

Only five countries switched their schedules immediately: Italy, Poland, Portugal, Spain, and the majority of France. Those places were deeply Roman Catholic, and they quickly decided to follow their pope’s calendar. But Protestant individuals and countries were more inclined to ignore papal bulls and continue on with their lives. Still, the Julian calendar had its problems, and a disjointed world (even a disjointed Western world) is tough to navigate.

In 1752, the year George Washington turned thirty and almost two centuries after October 15, 1582, Great Britain and its colonies flipped their calendars to Gregorian time. I envy my fellow Americans who made the switch—like Benjamin Franklin, who wrote at the time: “It is pleasant for an old man to be able to go to bed on September 2, and not have to get up until September 14.” But I have no jealousy of those who—also like Benjamin Franklin—scribbled both “O.S.” (Old Style) and “N.S.” (New Style) dates on their letters during the time between the New New Year (January 1) and the Old New Year (March 25). How strange and befuddling, to have lived in two months on one day.

As the centuries passed, and as Western countries grew in power and influence, the Gregorian calendar spread across the world—if inconsistently. The Orthodox church has never adopted the Gregorian calendar and still uses the Julian calendar to calculate its holidays. (This is why Catholics and Protestants will celebrate the resurrection on March 31 next year, and Orthodox Christians six weeks later on May 5.) Many Orthodox-dominated countries retained the Julian calendar for centuries, with their governments going Gregorian hundreds of years after others. Russia only started following the Gregorian calendar after the October Revolution in 1918—and years after Japan (1873), Korea (1876), and China (1912) had already made the switch.

A globally consistent calendar has its merits: for one, it makes setting the dates of political meetings and Olympic Games much easier. Even personally, I can understand the benefits: this fall, I’ve been setting up and attending meetings with book publishers from all over the world. We have enough trouble sorting out time zone differences; I can’t imagine the mishaps if we used two different dates to refer to next Thursday. Still, I grieve the different ways of existing in time that have been lost in the name of modernity and efficiency. Nothing disorients us quite like a different arrangement of time. As an American, I solidly prefer 10/15/2023 over 15/10/2023. The day must come after the month, not before! To many of my international colleagues, my standard arrangement is the unusual one. But on the practical side, I’m grateful that at least we can understand each other when we write the date for the Thursday after next.

Happy October 15—and also October 2 (in the Julian calendar), 30 Tishrei 5784 (in the Hebrew calendar), Bing Wu Day, Xin You Month, Gui Mao Year/the Year of the Rabbit (in the Chinese solar calendar), Rabiʻ I 30, 1445 AH (in the Umm-Al-Qura calendar), and so many more dates around the world.

Photo credit: image by rawpixel.com on Freepik

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