# 2431: Leap Year 2021

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 Leap Year 2021 Title text: I've lived in the present for my whole life and I'm not about to move now.

## Explanation

Cueball, checking his phone, comments on how fast time goes, saying it is already March. (This comic was posted on March 1, 2021.) Black Hat overhears him and says that it's actually February 29.

February 29 exists in the Gregorian calendar and its predecessor, the Julian calendar, as a correction mechanism for the fact that one tropical year on Earth is not exactly 365 days long. It's closer to 365.2422, and to prevent the dates from precessing relative to the seasons, an extra day is added once every fourth year, also called a leap year. This is still not enough to completely match Earth's orbital period, and for that reason the Gregorian calendar changed the leap year rules to be as follows: Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. This makes the average year 365.2425 days long, which approximates the 365.2422 days in the tropical year.

Black Hat wants every year to have a February 29, for no clear reason. Cueball acknowledges that he could accomplish this, if he could convince enough people to go along with it. Calendar systems are all invented, and whatever date systems are commonly acknowledged become the "correct" date. Cueball initially considers the change minor, assuming that they would simply change March 1st to February 29th on non-leap years, which would merely rename a single day and skip "March 1st" by going directly from February 29th to March 2nd. Black Hat clarifies that he actually wants to add another day, and the day AFTER that will be March 1. This could still be a minor change, if March were changed to a 30 day month on non-leap years, but Black Hat apparently wants the changes to propagate throughout the year. This would result in a 366-day year, causing the months to drift out of alignment with the seasons over the course of years, needlessly complicating time-keeping. Black Hat is unconcerned with the effect this will have on the "people of the future", and, as in the past, people around him are much more concerned about the time problems he's creating than he is. This once happened in ancient Egypt, where the priests had leap years every three years instead of every four years, so ancient Egypt had to have no leap years for several decades afterwards in order to fix the calendar.

In the last frame, Black Hat states that if the those people cared about the problems he's causing, "they shouldn't have decided to live in the future." Of course, it is at present impossible to choose the time period in which you live,[citation needed] yet Black Hat intends on penalizing them for it. Any number of positions could be proposed as a motive for his actions (for example, he may envy them for having the technology or benefits of the future, and wants to counteract that), but it is most likely that he is simply honing his sociopathic tendencies on a defenseless target.

In the title text, Cueball responds that this change would also cause issues for him, who is "living in the present", and he should not be forced to "move into the future". Alternatively, viewing the quote as a continuation of Black Hat's text at the end of the comic, he could mean that the effect of his new calendar is placed mostly on future people, and since he literally lives in the present and doesn't intend on traveling to the future, he can do what he wants without many repercussions. In this second interpretation, the phrase "move now" can be taken to have a double meaning: not only does Black Hat not intend to move presently, he also does not intend to move where the present currently is (i.e., move the "now" into the future).

## Transcript

[Cueball checking his phone in a narrow panel.]
Cueball: Can't believe it's already March.
Black Hat (off-screen): Nah, it's February 29th.
[Cueball has put his phone away and is standing next to Black Hat.]
Cueball: It's not a leap year.
Black Hat: I decided to make it one. Every year deserves to leap.
Cueball: Can you do that?
Black Hat: Can anyone stop me?
[Zoom in on Cueball.]
Cueball: I guess if you just encourage people to call March 1st "February 29th", they can go along with it if they want. Just a one-day renaming.
Black Hat (off-screen): No, tomorrow will be March 1st.
[Cueball standing to Black Hat, who is walking off screen to the right, with his finger raised.]
Cueball: So you're causing calendar drift for future generations.
Black Hat: If they didn't want to experience consequences, they shouldn't have decided to live in the future.

# Discussion

It's amazing how quickly some of us got to edit this. I hope I didn't cause too much edit-conflict confusion just by my changing the date value. Honestly just checked, before turning in, to find two (so far) other edits follow so quickly after... 141.101.98.152 02:03, 2 March 2021 (UTC)

Sorry,I did not see anything when I started

I wouldn't expect you to (the first Categories adder, yes?), until you perhaps tried to save. But that's what being shown edit-conflicts is important for. 141.101.98.244 03:02, 2 March 2021 (UTC)

If someone actually did this, how many years would it take for the calendar to line back up again where it started? 365? Captain Video (talk) 02:20, 2 March 2021 (UTC)

365 years plus (around) 33% more because every fourth year (except every hundredth, except except every 400th) is already expected to have a 29th, so you'd not be able to shift the year that year and have to do those days after the first 365 mostly-shifted consecutive years - with the necessary overflow days still being only to be done for 3/4(ish) of the next 91ish years, leaving maybe 23 more years to be shifted. But 24 years would only allow 18 shifts, so 6 more years than that probably would use 5 years. And one year may be absorbed already, or left over. So 365+91+23+6. Ish. Because it'd depend exactly which year you start as to which non-expandable years occur within the strict (0.75)+(0.25*0.75)+(0.25*0.25*0.75)+... series. But that's the likely area of the answer, off the top of my head. Around 485 years, give or take. Unless I've made a big error! 141.101.98.244 03:02, 2 March 2021 (UTC)
A quick evaluation of the geometric progression (a/1-r = 365/(1-1/4)) gives an answer of 486.666... This means it would take at least 487 years to come past full circle (488 on a leap year) if not for the pesky 400-year rule. Given where the date lies, there can be either one or two per cycle; thus, we find a minimum of 488 years and a maximum of 490. If we started this current year, on a non-leap year with no round 400 in the next 87 years, it would take the minimum amount, 488 years, to cycle through 489 revolutions of the Earth around the Sun. Happy Leap Year, my friends! BlackHat (talk) 03:52, 2 March 2021 (UTC)
It's a bit messier, but the rough calculation was indeed close. I did a quick Excel calculation (well, OpenOffice Calc, but essentially the same - easiest thing at hand without Perl-diving). Actual 'next synchronised' period is 482-484 (solar) years, in an intruiging but not surprising pattern. Prior to 2000's unusual leap-day (but not too early to miss encompassing the one in 2400) it is 484 actual years (483 uniformly 'enhanced' ones) - but if you start in the period of any year leading up to a LD (I was running of 28th of February baselines, but any time from March 1st the prior year would count) you get the 485th year meshed too. (These periods contain two quatrocentenial LDs. And obviously starting with a 'normal' leap-year means the very next year is just as accurate, before it gets shifted the year after.)
2001 until the late 2010s it's one set of 483 years to three of 484 (one of each has two synchronised years, 484th and 485th, because of adjacent starts landing on the same end), having just one century LD within. As you get close to 2020 you get a further non-LD century in (2020+480_and_change is 2500+) and 482 and/or 483 actual-years. "And/or" because only every second 482 ends on run-up to a LD so that the 483rd meshes as well, the 483s are not meshed correctly to do the same.
The cycle beyond that is individually roaming through the same 482 to 484 range (and a number of end-point adjacents) but as it plays hopscotch through and around the centennial patterns it adopts an off-rhythm variation that doesn't even really make simple sense at the millenial level, as you might imagine. It might make an interesting artistic 'regularly purturbed noise' at even longer sample-sizes, though. Hack it into a graphical format, maybe, various possible options according to taste. 141.101.99.193 08:22, 2 March 2021 (UTC)
It would take 365.25 years that have the "extra" leap day for the years to sync back up. For every 400 years there are 303 such years (3 of every 4 years + years 100, 200, and 300). So it would take 365.25 * (400 / 303) = 482.18 years. Plus one year if the 400-year leap year comes up twice.

Can someone make a Category:Calendar that is a subcategory of Category:Time? I feel like there are several comics that could fit, e.g. 994: Advent Calendar, 1140: Calendar of Meaningful Dates, 1930: Calendar Facts, 1073: Weekend, 1061: EST, etc. 162.158.255.210 02:39, 2 March 2021 (UTC)

Sweden tried something like this in the early 18th century. When switching from Julian to Gregorian calendar, some bright spark decided to do it gradually, by removing all leap days between 1700 and 1740. The leap day of 1700 was skipped (It was a leap day in the Julian calendar, but not the Gregorian), but due to war and other things they 'forgot' to annul the leap days of 1704 and 1708. In 1712 it was decided to revert to Gregorian calendar, by adding a double leap day, resulting in the only known occurrence of February 30. From 1700 to 1712 Sweden was out of sync with both the Gregorian and Julian calendars, resulting in quite a lot of confusion. For example, Carl Linnaeus birthday can be given as May 12, 13 or 23, depending on what calendar is used. Popup (talk) 07:22, 2 March 2021 (UTC)

I disagree with the explanation of the title text. I understood it to be spoken by Black Hat to reinforce his disregard of people who might suffer in the future since he lives firmly in the present, one day at a time, as it were. Rtanenbaum (talk) 12:54, 2 March 2021 (UTC)

My take on the title text was just a reference to the common statement (esp. as people get older), "I've lived in <city/state/etc.> for my whole life and I'm not about to move now." 172.68.65.222 15:39, 2 March 2021 (UTC)Pat

I don't see why the explanation is incomplete. Can someone please tell me why so I can fix it? Quillathe Siannodel (talk) 17:17, 2 March 2021 (UTC)

I think the title text is black hat using "living in the present" as a justification for causing unnecessary problems in the future. 172.69.34.148 19:51, 2 March 2021 (UTC)

There needs to be some reference to how "living in the present" has a different meaning than "living at some time which is neither the past nor the future." It can also mean that they "live for today" or that "they are aware of that happens around them" or other, similar platitude. Cwallenpoole (talk) 20:27, 2 March 2021 (UTC)

Another interpretation of the title text is that the calendar only affects people who (live in/plan for) the future, as in those concerned about events other than those in the present. As a calandar is arguably useless to those who don't plan for future events, such a change would not really affect them.

For me, the comic itself was not available until the day after it was expected (March 2, 2021). I wonder if this was deliberate, and refers to how we readers often use the regularity of the xkcd comics as a calendar. Anyway to check the actual (Gregorian) date it was posted? Will future comics now be released on Tuesdays Thursdays Saturdays, until leap year 2022? 172.69.55.164 06:21, 4 March 2021 (UTC)

2022? Don't you mean 2024? 162.158.63.60 07:56, 4 March 2021 (UTC)
Every year deserves to leap. BlackHat (talk) 04:17, 5 March 2021 (UTC)
https://www.explainxkcd.com/wiki/index.php?title=2431:_Leap_Year_2021&oldid=206922. ;) 162.158.155.72 11:43, 5 March 2021 (UTC)