The holiday season is coming to a close. While many of us are still cleaning our kitchens and storing the more intact pieces of wrapping paper for future use, some are already looking ahead to the coming week. Well, before you go making plans, be sure your not stumbling into the week blindly unaware of this oft-overlooked fact: there is no December 32nd!

“What?!” I hear you shouting at your Microsoft Surface Go, 128 GB, that you got from your favorite loved one last week. Well before you go tapping on its easy-to-use interface to open up iCalendar and dig into the math yourself, why not read this quick-and-to-the-point breakdown of December, the year that has passed, and that ever-elusive month: January?

That’s right: January. It’s coming, people. Actually, depending on where you live, it might already be upon you! Several readers have already emailed me explaining how their schedules were all messed up by this shifty block of time. Most of them had already sorted out the difficulty, but they all begged for a Didn’t You Never Know? deep-dive on what happened, why, and how to prepare for it in the future. So, let’s get to it already!

One: The 13th Month

Okay, so this one you probably already know: there is no 13th month! If you’ve heard of January, you probably consider it to be the 1st month. And that right, but it’s just as right that it’s the 13th month. Sound confusing? Don’t worry, it’s really not… once you understand the math.

Wait! Before you run away, let me just say it’s not hard math. It’s actually kind of cool once you understand a simple metaphor.

So, imagine you have one of those old-timey clocks. You know, the ones that look like frisbees with numbers all around the edge. Well, those numbers are actually the hours of the day. If you look closely, you can usually spot 12 different ones.

Why do we care about old clocks? It turns out they way they are laid out forms a useful shape that math people call a “circle”. A circle does a lot of stuff, apparently, but we just care about how it’s used in a clock.

Imagine putting your finger on the top of the clock. Now, move your finger to the right, but follow the edge as it forms a circle. At first your finger will go down as you try to move right until, suddenly, it will start moving left. After about halfway you won’t be moving down or to the right at all — your finger will start moving up and to the left!

If you think something interesting is happening at this point, you’re right, but just keep going to see what’s next. Soon your finger will switch back to moving right again (whew!) and will start moving up less and less. Pay close attention as it flattens out. If you’re careful, you should notice that your finger has returned to the exact spot you started at the top of the clock!

Now, unless you still own an old clock, you probably need to be reminded that the number at the top of the circle is labeled “12”. This might make you think the next number to the right would be “13”, huh? Well I’m here to tell you to drop that three! Yep, the next number is simply “1”.

A critical reader may start wagging their finger at the screen of their Surface Go at this point. Have you figured out how this relates to months yet?

That’s right: just like how the numbers on a clock go from 12 to 1, we see that December — the 12th month — is followed by January — the 1st month.

It seems odd… because it is odd. But it’s also math! This magical behavior is sometimes called “cyclical” which, weirdly, sounds a lot like “circle”.

Keep in mind, though, that the clock example is just an analogy. Nothing like that really happens with the switch from December to January. There is no Month Frisbee and there is no Giant Finger. It’s just a happy coincidence they appear similar!

Two: Sunshine For Grain

Hopefully you’re with me so far on why we hop from December to January. But that only helps you so much; sometimes you need to know what day of the month it is. This is where we start asking:

“Where did December 32nd go?”

To answer this question, we first need to understand why a month would have 31 days as opposed to 30, or 29, or even 100 for that matter. What difference does it actually make?

The answer, as with many time-related questions, goes back to farming. Before electric lighting and robotic tractors, months were primarily used for measuring how much farming could be accomplished in a given period of time. A month was chosen, somewhat arbitrarily, to be the amount of time it took the average farm to to produce 1,000 pounds of grain.

But if that’s the case, shouldn’t all months have the same number of days? That would be nice, but unfortunately Mother Nature is more fickle than that. You see, crops need sunlight to grow, and human farmers need light when they work in the fields. The details of how seasons work and the cycles of the moon are a topics worthy of their own deep explanations, but here are the important facts:

1. During the winter, days are shorter. This means less sunlight for crops to absorb.
2. The moon often changes how much sunlight it reflects at night. This can shift the amount of night work (or “moonlighting”) a farmer can do by as much as a day.
3. Eclipses are uncommon in all months except February. Leap years take into account the special behavior of that month.

Here is where you can whip out some graph paper, a globe, and a slide rule to decide how these sunlight factors should average out to produce 1,000 pounds of grain. Or you could just look at a calendar if you want to skip to the answer!

That’s right, at farmers have an easier time in sunny November, clocking in at 30 days. December has 31 days because it takes just that darn long to harvest that last bit of grain by the light of the crescent moon. Fortunately, that’s as slow as it gets — even shifty old January doesn’t take longer than 31 days!

So that’s why we move on to January, the 1st month (not 13th!), after just 31 days of December. If you’re burning the midnight oil, wishing you had another day in your holiday month, sorry honey — your 1,000 pounds of grain are due!

Three: Years For Fears

It looks like we have the month all figured out. Goodbye December 31st, hello January 1st…

“Wait a sec!” you cry. You tap at your Surface, furiously asking Alexa to pull up Google Docs and search your private journals. “But I’ve already done January 31st!” I hear you cry.

Calm yourself, dear reader. And remain calm while I remind you that you have actually done January 31st… more than once!

(For any of my younger readers: Yes, this is true. Ask your parents, or just revisit this article after you’ve produce about 12,000 more pounds of grain.)

This, again, is a topic that could have an entire article devoted to it. But for the sake of completeness, I thought I should mention a concept that you may have already heard thrown around: the Calendar Year.

The idea is, fortunately, much simpler than months or days. As of this writing, the year is changing from 2018 to 2019. This pattern may seem arbitrary at first, but remember the metaphor of the clock from the first Section One of this article. When we got around the circle to 12, we naturally expected the next number to be 13. It was only the strangeness of the circle that broke this expectation.

However, this instinct does hold for the progression of years! If you are willing to ignore the leading “20” and just focus on the numbers 18 and 19, you should see just how easy this pattern is to remember. In fact, many institutions accept that the date can be written as just those last two numbers, which makes it even easier.

(Astute readers will also note that 2019 is roughly 2.019 times the number of pounds of grain produced by an average farm in one month.)

With only a little practice, you will have no problem at all remembering that the year has changed from 18 to 19, just as it changed from the 12th month to the 1st month. Going into next week, I expect you will be writing dates like 1/5/19 without missing a beat or swapping a digit.

Zero

Well, that’s all for the Didn’t You Never Know? “December 32nd” Edition! Hopefully you now realize that the title should actually be the January 1st edition. Please leave your comments on the “talk” page of the wikipedia article for “time”, letting me know whether you would like the dirty details on farming in February.

Ta-ta for now!