1935: "2018"

[orthogon]

The Gregorian calendar was created to stabilise the date of Easter ...

This "Easter" to which you refer: is this the festival whose date can vary by five weeks from one year to the next? Thank goodness they added that one-day fix every 400 years.

[rmsgrey]

The Gregorian calendar was created to stabilise the date of Easter ...

This "Easter" to which you refer: is this the festival whose date can vary by five weeks from one year to the next? Thank goodness they added that one-day fix every 400 years.

Wasn't it 3 days every 400 years - dropping the 00s except every 4th, rather than adding every 400th?

[orthogon]

The Gregorian calendar was created to stabilise the date of Easter ...

This "Easter" to which you refer: is this the festival whose date can vary by five weeks from one year to the next? Thank goodness they added that one-day fix every 400 years.

Wasn't it 3 days every 400 years - dropping the 00s except every 4th, rather than adding every 400th?

Oh, I don't know what the historical sequence was; I was just referring to orders of approximation:
0th order: 365 days every year
1st order: an extra day every 4 years
2nd order: one fewer day every 100 years
3rd order: one extra day every 400 years.

I find it a bit suspicious that the 400 year cycle contains a whole number of weeks. I suppose there was a one-in-seven chance of that happening without setting out to achieve it, but, well, it just feels a bit too good to be a coincidence.

[gmalivuk]

The Gregorian fix included the 2nd and 3rd orders together, amounting to a correction (compared to the Julian calendar) of 3 days every 4 centuries.

Compared to the vernal equinox year mentioned above, that correction improves from a Julian error of one day every 131 years to a Gregorian error of one day every 7937 years.

[Keyman]

Or....

Turn to the second page of the new calendar your administrative assistant has so efficiently provided for you.

If there's 29 days, it's a leap year.
If there's 28 it's a regular year.
If there's more than 29, it's a joke.

[Soupspoon]

a Julian error of one day every 131 years

The Julian error was to trust Brutus…

[da Doctah]

Or....

Turn to the second page of the new calendar your administrative assistant has so efficiently provided for you.

If there's 29 days, it's a leap year.
If there's 28 it's a regular year.
If there's more than 29, it's a joke.

Or it's one of those "16-month" calendars they sell in mall kiosks, that start in September. Many have pictures of cats on each page, grumpy and otherwise.

[Keyman]

Or....

Turn to the second page of the new calendar your administrative assistant has so efficiently provided for you.

If there's 29 days, it's a leap year.
If there's 28 it's a regular year.
If there's more than 29, it's a joke.

Or it's one of those "16-month" calendars they sell in mall kiosks, that start in September. Many have pictures of cats on each page, grumpy and otherwise.

OK...just turn to Meowbruary.

[Reka]

Or it's one of those "16-month" calendars they sell in mall kiosks, that start in September. Many have pictures of cats on each page, grumpy and otherwise.

16-month calendars are a lie: they only ever have 13 pages, never 16. September-December of the first year are all smooshed together on one page. I have also never understood the point of starting in September: I mean, who doesn't have a calendar already by that point? If you want to make an actually-useful 16-month calendar, it needs to go from January of year 1 to April of year 2.

Also, I want to register a complaint against my sister: she didn't make a niece-calendar this year, so my office wall is woefully bare. (See above about actually-useful 16-month calendars.) I mean, I know the niece is now ancient, all of 7 (and a half) years old, and therefore no longer falls under the cute-baby-pictures rubric, but I have been trained to expect certain things under the tree. Harumph.

[Soupspoon]

I have also never understood the point of starting in September: I mean, who doesn't have a calendar already by that point?

So, you think that it's of no use and all academic?

While I think it's probably useful because it's academic.

[ucim]

Also, I want to register a complaint against my sister: she didn't make a niece-calendar this year, so my office wall is woefully bare.

Feel free to download and print the Ecclesiastical Calendar of the Order of the Holy Contradiction, and to join the One True Thread to learn how it came about.

Jose

[Brian-M]

Simple solution — take the last two digits of the calendar year (2018 would be 18, for example).  Can you divide that two-digit number evenly by four?   If the answer is 'yes', then it's a leap year.

That method might have worked for the Julian calendar, but it's only 99.25% accurate with the Gregorian calendar we use today.

(Because the Gregorian calendar skips 3 leap years every 4 centuries, so dividing by 4 only has a 397/400 or 0.9925 chance of being right.)

[Keyman]

Also, I want to register a complaint against my sister: she didn't make a niece-calendar this year, so my office wall is woefully bare.

Feel free to download and print the Ecclesiastical Calendar of the Order of the Holy Contradiction, and to join the One True Thread to learn how it came about.

Jose

I clicked your calendar link and corporate's Net Nanny says no-no.

The reason the website is being blocked: Corporate Defined Block
Sites that are not currently rated or that cannot be rated into any other category.

Not quite sure how OTTers will feel about it, but I suppose "cannot be rated into any other category" isn't surprising.

[Mutex]

Simple solution to this nonsense: Strap rockets onto the Earth and push it into a slightly lower orbit, so a year is exactly 365 days. In fact, lets push it even closer so it's 360 days so it's easily dividable.

[ucim]

I clicked your calendar link and corporate's Net Nanny says no-no.

You need a better nanny.

chirpingmustard.com is a redirect site for OTTers to put stuff. Here's the direct link to the calendar: http://stickywords.com/xkcd/xkcdcalendar.php (stickywords.com is my own hosting site). But it's probably unclassified too, as it's a tiny island in the great sea that is the internet of tubes.

Jose

[Soupspoon]

Change the Earth's spin, while we're at it. Adjust the number of seconds per day to something round (or per year, but per day starts you out on that path) or choose a spin-rate and newSecond completely to your own liking. Match that up with the new orbit (might have to be out, so now we have a use for the Greenhouse Gases, maybe better than having to adjust to too much sun energy) and don't forget to factor in the new sidereal drift from the start

Do it right, and we can go full Metric Time and Metric Calendar, the 'easy' way.

[ucim]

Do it right, and we can go full Metric Time and Metric Calendar, the 'easy' way.

Such small goals! Do it really right and we can go full cubic time!

Jose

[gmalivuk]

Or it's one of those "16-month" calendars they sell in mall kiosks, that start in September. Many have pictures of cats on each page, grumpy and otherwise.

16-month calendars are a lie: they only ever have 13 pages, never 16. September-December of the first year are all smooshed together on one page.

This is not true, you apparently just haven't seen the useful kind before.

I have also never understood the point of starting in September: I mean, who doesn't have a calendar already by that point?

Are you from a place where the school year doesn't typically start in September?

[Lothario O'Leary]

The mean tropical year is measured at 365.24219 days, but is gradually getting smaller because the slowing of the earth's rotation is making the days longer. This means that in the long-run my system would be more accurate than either of those proposals.

In discussions like this one the mean Gregorian year length is often compared to the mean tropical year. However, that comparison may not be appropriate. The Gregorian calendar was created to stabilise the date of Easter, which is tied to the date of the (northern hemisphere) spring equinox. So rather than using the mean tropical year we should be using the vernal equinox year, which is (to 6 decimal places) 365.242374 days.

Astronomer Duncan Steel has discussed this point in several publications, including his popular book Marking Time: The Epic Quest to Invent the Perfect Calendar. Here's a short PDF that summarises his argument: The proper length of a calendar year. There's also some interesting information in his story about the the non-implemented 33-year English Protestant Calendar; there are further details of this intriguing theory in Marking Time.

Wikipedia defines the tropical year as the vernal equinox year, and then proceeds to give the traditional 365.24219 figure. I am not exactly sure how is the 365.242374 supposed to work - are the March and September equinoxes getting closer to each other?
[EDIT: I've found the citation, also in Wikipedia; if those figures are correct, chances are it's probably a cyclical thing, and 365.24219 is what happens when we smooth those cycles away.]

In any case, true March equinox years float by as much as 30 minutes (about 0.02 days), so any "mean year" definition would have to average it in a very long period. I'm not sure whether a figure "to six decimal places" even makes sense - the length of a year in mean solar days (which would be equivalent to calendar days assuming continuing application of leap seconds) decreases by about a second (or 0.00001 days) per century.

I do somewhat like the idea of a 33-year calendar keeping the equinox on the same GMT-5 day. (Reminds me of the Sothic cycle and its relationship to the Julian calendar.)
But I still think that a 128-year cycle would be more convenient (especially on modern binary-based computers, where it corresponds to a year 16D.3E₁₆ days long), and it happens to be a lot closer to the modern mean tropical year (exact in SI days as of April 5, 2035, if I interpreted the Wikipedia formula correctly; not sure when, if ever, it was or will be exact in mean solar days).

[EDIT: fixed my hexadecimal math]
[EDIT 2: fixed it incorrectly, so fixed again]
[EDIT 3: added the edit notices]

[orthogon]

I've been down the same rabbit-hole too. It turns out that, yes, the equinoxes and solstices do move relative to one another in terms of time. Given they're equally spaced in angle, around the elliptical orbit, they're not equally spaced in time. Because the precession makes them move around the orbit, this temporal spacing changes over time. Over the long-ish term, this would average out, but the precession is only an50 arc seconds per year, so for many centuries the years will consistently be of different lengths.

Edit: corrected the rate of precession. The paragraph here just before "mean time interval between equinoxes" explains it.

ETA2: My explanation was inside out. The ellipticity makes them unequally spaced in time, whilst the precession makes this spacing change over the years.

ETA3: I think it's correct now!

ETA4: The fact that the perihelion is close to the southern solstice at present must mean that the effects are maximised/minimised. My first impression is that the equinoxes ought to be at similar radii, so the two equinoctial years ought to be similar; both equinoxes ought to be about the same time before/after the southern solstice. I may well be wrong though.

ETA5: * Googles * well blow me if it wasn't at 5.34UTC this morning! Happy Perihelion everyone!

[Reka]

I have also never understood the point of starting in September: I mean, who doesn't have a calendar already by that point?

Are you from a place where the school year doesn't typically start in September?

Does your existing calendar go "Oops, new academic year, must self-destruct"?

(Also, my work is academia-adjacent, and almost all of our clients start the new academic year in June or July. Starting in September is for the young folks who still have the luxury of taking the summer off. Or actually, scratch that: the above-mentioned niece started school in August. [Which is an atrocity in its own right, but I digress.] So I still utterly fail to see the utility of a calendar that starts in September.)

[Old Bruce]

... I still utterly fail to see the utility of a calendar that starts in September.)

In my life there was one time it would have been nice to have a September starting calendar, but back then we were poor enough it would've fallen into the luxury category and been un-purchased. We waited until the bank gave out a free one three months later.

[sam_i_am]

So, under the kayfabe that large numbers being difficult to factor implies that it's difficult to determine if a large number is divisible by 4:

Why do we assume that it's easy to determine if it's divisible by 4 if it's odd?

[chridd]

Why do we assume that it's easy to determine if it's divisible by 4 if it's odd?

People have been using supercomputers to go through all the odd numbers to test the conjecture that none of them are divisible by four. After *mumble* computation time, we now know that if there's an odd number divisible by four, then it's at least 10⁵.

[xtifr]

Why do we assume that it's easy to determine if it's divisible by 4 if it's odd?

People have been using supercomputers to go through all the odd numbers to test the conjecture that none of them are divisible by four. After *mumble* computation time, we now know that if there's an odd number divisible by four, then it's at least 10⁵.

Actually, I believe it's been proven that all multiples of four are odd.

Spoiler:

For any multiple of four (or any other number, for that matter), there are an infinite number of numbers which are not that number, but only one which is that number. Therefore, that number (like all numbers) is an odd one--normal numbers are almost all some other number entirely.

[Cougar Allen]

Simple solution to this nonsense: Strap rockets onto the Earth and push it into a slightly lower orbit, so a year is exactly 365 days. In fact, lets push it even closer so it's 360 days so it's easily dividable.

Ackkkkkkkkkk! Global warming! Let's push it out to make the year 400 days. Then we can have four seasons of 100 days each and there will be nothing to cry about.

https://www.youtube.com/watch?v=40bTOCv3_ak

[Eshru]

And four 25 day months per season to boot! And we can move seasons back to wherever their names suggest they ought to while we're at it.

Edit:
5 day weeks alternating 3 and 4 workdays per week in a 4/3/4/3/4 pattern except in one season where we have a 3/4/3/4/3 pattern. This keeps the days worked/off ratio close enough to what it is now, with fewer days worked consecutively. (Disclaimer: math done in my head)