When Is (American) Thanksgiving Most Likely To Happen?


Today (the 26th of November) is the Thanksgiving holiday in the United States. The holiday’s set, by law since 1941, to the fourth Thursday in November. (Before then it was customarily the last Thursday in November, but set by Presidential declaration. After Franklin Delano Roosevelt set the holiday to the third Thursday in November, to extend the 1939 and 1940 Christmas-shopping seasons — a decision Republican Alf Landon characterized as Hitlerian — the fourth Thursday was encoded in law.)

Any know-it-all will tell you, though, how the 13th of the month is very slightly more likely to be a Friday than any other day of the week. This is because the Gregorian calendar has that peculiar century-year leap day rule. It throws off the regular progression of the dates through the week. It takes 400 years for the calendar to start repeating itself. How does this affect the fourth Thursday of November? (A month which, this year, did have a Friday the 13th.)

It turns out, it changes things in subtle ways. Thanksgiving, by the current rule, can be any date between the 22nd and 28th; it’s most likely to be any of the 22nd, 24th, or 26th. (This implies that the 13th of November is equally likely to be a Friday, Wednesday, or Monday, a result that surprises me too.) So here’s how often which date is Thanksgiving. This if we pretend the current United States definition of Thanksgiving will be in force for 400 years unchanged:

November Will Be Thanksgiving
22 58
23 56
24 58
25 56
26 58
27 57
28 57
times in 400 years

I hope this helps your planning, somehow.

When Is Thanksgiving Most Likely To Happen?


I thought I had written this up. Which is good because I didn’t want to spend the energy redoing these calculations.

The date of Thanksgiving, as observed in the United States, is that it’s the fourth Thursday of November. So it might happen anytime from the 22nd through the 28th. But because of the quirks of the Gregorian calendar, it can happen that a particular date, like the 23rd of November, is more or less likely to be a Thursday than some other day of the week.

So here’s the results of what days are most and least likely to be Thanksgiving. It turns out the 23rd, this year’s candidate, is tied for the rarest of Thanksgiving days. It’s not that rare, in comparison. It happens only two fewer times every 400 years than do Thanksgivings on the 22nd of November, the (tied) most common day.

Reading the Comics, April 4, 2016: Precursor To April 5 Edition


Comic Strip Master Command followed up its slow times with a rush of comic strips I can talk about. Or that I can sort-of talk about. There’s enough for a regular essay just about the comics from the 5th of April alone. So today’s Reading the Comics entry is just the strips up through the 4th of April. That makes for a slightly short collection but what can I do besides schedule these for a consistent day of the week regardless of how many comics there are to talk about?

Dave Whamond’s Reality Check for the 3rd of April mentions the infinite-monkeys tale. And it even does so in iconic form, in talking about writing Shakespeare’s Hamlet. I don’t mean to disparage the comic, especially when it’s put five punch lines into the panel. (I admit I’m a little disappointed when a Sunday strip is the same one- or three-panel format as a regular daily comic, though.) But I’m pretty sure this same premise was done by Fred Allen on the radio sometime around 1940. I don’t think that mentioned the infinite monkeys, though.

Missy Meyer’s Holiday Doodles for the 4th of April mentioned that it was Square Root Day. I am curious whether the comic will mention anything for the 9th of April. I have noticed some people muttering about this Perfect Squares Day. Also I’m surprised that “glases with tape over the bridge” is still a signifier of square-ness.

Brandon Sheffield and Dami Lee’s Hot Comics for Cool People for the 4th titles its installment Perfect Geometry Comics. And it presents, as often will happen, some muddle of algebra and geometry as the way to work out a brilliantly perfect solution. Also, the comic features a dog in safety goggles, which is always good to see.

Graham Nolan’s Sunshine State for the 4th presents a word problem that might be a good introduction to asymptotes. The ratio of two people’s ages will approach without ever quite equalling 1. But it will, if the people last long enough, come as close as one might want. There’s probably also a good lesson to be made by comparing this age problem to the problem of Achilles and the tortoise.

Reading the Comics, March 14, 2016: Pi Day Comics Event


Comic Strip Master Command had the regular pace of mathematically-themed comic strips the last few days. But it remembered what the 14th would be. You’ll see that when we get there.

Ray Billingsley’s Curtis for the 11th of March is a student-resists-the-word-problem joke. But it’s a more interesting word problem than usual. It’s your classic problem of two trains meeting, but rather than ask when they’ll meet it asks where. It’s just an extra little step once the time of meeting is made, but that’s all right by me. Anything to freshen the scenario up.

'Please answer this math question, Mr Wilkins. John is traveling east from San Francisco on a train at a speed of 80 miles per hour. Tom is going to that same meeting from New York, headed west, on a train traveling 100 miles per hour. In what state will they meet?' 'Couldn't they just Skype?'
Ray Billingsley’s Curtis for the 11th of March, 2016. I am curious what the path of the rail line is.

Tony Carrillo’s F Minus for the 11th was apparently our Venn Diagram joke for the week. I’m amused.

Mason Mastroianni, Mick Mastroianni, and Perri Hart’s B.C. for the 12th of March name-drops statisticians. Statisticians are almost expected to produce interesting pictures of their results. It is the field that gave us bar charts, pie charts, scatter plots, and many more. Statistics is, in part, about understanding a complicated set of data with a few numbers. It’s also about turning those numbers into recognizable pictures, all in the hope of finding meaning in a confusing world (ours).

Brian Anderson’s Dog Eat Doug for the 13th of March uses walls full of mathematical scrawl as signifier for “stuff thought deeply about’. I don’t recognize any of the symbols specifically, although some of them look plausibly like calculus. I would not be surprised if Anderson had copied equations from a book on string theory. I’d do it to tell this joke.

And then came the 14th of March. That gave us a bounty of Pi Day comics. Among them:

'Happy Pi Day.' 'Mmm. I love apple pie.' 'Pi day, not Pie Day. Pi ... you know ... 3.14 ... March 14th. Get it?' 'Today is a pie-eating holiday?' 'Sort of. They do celebrate it with pie, but it's mostly about pi.' 'I don't understand what that kid says half the time.'
John Hambrock’s The Brilliant Mind of Edison Lee for the 14th of March, 2016. The strip is like this a lot.

John Hambrock’s The Brilliant Mind of Edison Lee trusts that the name of the day is wordplay enough.

Scott Hilburn’s The Argyle Sweater is also a wordplay joke, although it’s a bit more advanced.

Tim Rickard’s Brewster Rockit fuses the pun with one of its running, or at least rolling, gags.

Bill Whitehead’s Free Range makes an urban legend out of the obsessive calculation of digits of π.

And Missy Meyer’s informational panel cartoon Holiday Doodles mentions that besides “National” Pi Day it was also “National” Potato Chip Day, “National” Children’s Craft Day, and “International” Ask A Question Day. My question: for the first three days, which nation?

Edited To Add: And I forgot to mention, after noting to myself that I ought to mention it. The Price Is Right (the United States edition) hopped onto the Pi Day fuss. It used the day as a thematic link for its Showcase prize packages, noting how you could work out π from the circumference of your new bicycles, or how π was a letter from your vacation destination of Greece, and if you think there weren’t brand-new cars in both Showcases you don’t know the game show well. Did anyone learn anything mathematical from this? I am skeptical. Do people come away thinking mathematics is more fun after this? … Conceivably. At least it was a day fairly free of people declaring they Hate Math and Can Never Do It.

Reading the Comics, September 24, 2015: Yes, I Do So Edition


Yes, in this roundup of mathematically-themed comic strips I talk seriously about the educational techniques of the fictional Great Smokey Mountains community where the comic strip Barney Google and Snuffy Smith takes place. I accept the implications of this.

John Rose’s Barney Google And Snuffy Smith for the 23rd of September is your standard snarky-response joke. I’m a bit surprised to see that at whatever class level Jughaid’s in they’re using “x” to stand in for the not-yet-known number. I thought empty boxes or question marks were more common. But I also think Miz Prunelly’s not working most effectively by getting angry at Jughaid for not knowing what x is.

Miz Prunelly asks Jughaid what the 'x' in the equation 3 + x = 8 stands for. He insists he doesn't know. She says she'll only ask him one more time. He says that's a relief as he still doesn't know.
John Rose’s Barney Google And Snuffy Smith for the 23rd of September, 2015.

I would suggest trying this: can Jughaid find some possible values of x that are definitely too small? And some possible values that are certainly too big? Then what kinds of numbers are both not-too-small and not-too-big? One standard mathematician’s trick for finding an unknown quantity is to show that it can’t be smaller than some number, giving us a lower bound. And then show it can’t be larger than some number, giving us an upper bound. If the lower bound and the upper bound are the same number, we’re done. If they’re not the same number we might have to go looking, but at least we’ve got a better idea what a correct answer should look like. If the lower bound is a larger number than the upper bound, we have to go back and check whether there actually is an answer, or if we started off in the wrong direction.

Scott Adams’s Dilbert Classics for the 23rd of September (a rerun from the 30th of July, 1992) mentions “conversational geometry”. It’s built on a bit of geometry that somehow escaped into being a common allusion, and that occasionally riles up grammar nerds. The problem is trying to use “turned around 360 degrees” for “turned completely around”. 360 degrees is certainly turning something all the way around, but it leaves the thing back where it started, apparently unchanged. (Well, there are some oddball structures where you can rotate something 360 degrees and have it not back the way it started, but those only occur in abstract mathematical constructions and in some — not all! — subatomic particles. Yes, it’s weird. It’s like that.)

The grammar nerd will insist that what’s meant is to turn something 180 degrees, reversing its direction. Or maybe changed 90 degrees, looking perpendicular to whatever the original situation was. Personally I can’t get upset about a shorthand English phrase not making literal sense, because there are only about six shorthand English phrases that make even the slightest literal sense, and four of those are tapas orders. Eventually you have to stop with the rage and just say something already. And rotating 360 degrees is a different process from rotating not at all. You move, you break your focus, you break your attention. Even if you face the same things again you face them having refreshed your perceptions. You might now see something you had not before.

John Zakour and Scott Roberts’s Maria’s Day for the 23rd of September asserts that mathematics is important so that one can check one’s accountants. This is true, although it’s hardly everything mathematics is enjoyable for. And while I don’t often get to call attention to comic strip artwork, do look at the different papers; there’s some fun there.

Pab Sungenis’s New Adventures of Queen Victoria for the 24th of September — and the days around it — have seen Victoria and Nikola Tesla facing the end result of too much holiday creep: a holiday singularity. By a singularity a mathematician means a point where stuff gets weird: where a function isn’t defined, where a surface breaks off, where several independent solutions suddenly stop being independent, that sort of thing. It’ll often correspond with some measure becoming infinitely large (as a positive or a negative number), though I don’t think it’s safe to say that always happens.

We generally can’t say what’s happening at a singularity. But the existence of a singularity, and what it behaves like, can tell us something about what’s happening away from the singularity. It can happen, for example, that a singularity is removable. That is, if a function is undefined for some values, perhaps we can come up with a logically compelling definition for what it might do at those values. If you can remove a singularity then we call this a “removable singularity”. This serves to show you don’t necessarily need grad school to understand everything mathematicians are saying. Sometimes a singularity can’t be removed, and those are known as “nonremovable singularities” or “essential singularities” or sometimes some other nastier names.

Usually, if one has a singularity in a mathematical construct, then information about one side of the singularity isn’t enough to extrapolate what might be on the other side. This makes the literary use of a “singularity” as “something magical that does whatever the plot requires” justified enough. Tesla here is clearly using the idea of reaching an infinitely vast, or an infinitely dense, holiday concentration as a singularity. I grant that would be singular enough. The strip does make me think of a fun sequence in Walt Kelly’s Pogo where one year the Bun Rabbit decided to get all the holiday-celebrating done first thing in the year, to clear out the rest. He went about banging the drum and listing every holiday ever, which is what made me aware of the New Jersey Big Sea Day.

Shaenon K Garrity and Jeffrey C Wells’s Skin Horse for the 24th of September includes a sequence identified as the “Catalan Series”. I’d have said “sequence” myself. The Catalan sequence describes (among other things) how many ways you can break down a regular polygon into a particular number of triangles. A square can be broken down into two triangles just two ways (if orientation counts, which for this problem, it does). A pentagon can be broken down into three triangles in five ways. A hexagon can be broken down into four triangles in fourteen ways, and so on. (The key is you break the polygon into a number of triangles that’s two less than the number of sides. So if you had a 9-sided polygon, you’d break it up into 7 triangles. If you had a 20-sided polygon, you’d break it up into 18 triangles.) The sequence describes more stuff than that, but this is an easy-to-understand application. As the name of the sequence suggests, it comes to us from the Belgian-French mathematician Eugène Charles Catalan (1814 – 1894).

Catalan’s name also might be faintly familiar for a conjecture he posed in 1844, which was finally proven true in 2002 by Preda Mihăilescu. His conjecture is based on observing that the number 2 raised to the third power is 8, while the number 3 raised to the second power is 9, quite close together. Catalan conjectured this was the only case of consecutive powers. That is, there’s nothing like 15 to the twentieth power being one less than 12 to the twenty-fourth power or anything like that. I’m afraid I don’t know enough of this kind of mathematics, known as number theory, to say whether that’s of use for anything more than settling curiosity on the point.