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bennyp101

"Months have either 28, 29, 30, or 31 days."

Ok, Im intrigued, are there months that don't? I assume it must be a country specific thing?

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Adoption of the Gregorian calendar [1] resulted in a number of short months in a bunch of countries.

Different but related, 46 BC, the year of adoption of the Julian calendar, had 15 months [2].

[1]: https://en.wikipedia.org/wiki/Adoption_of_the_Gregorian_cale...

[2]: https://www.uh.edu/engines/epi2364.htm

That's what I thought. This list mixes "falsehoods" that nobody with a bit of common sense - even children - would believe, and pedantry that could be useful to 0.001% of developers. For most programs, Time starts in 1970.

IMO, this list is only good at... wasting time. Except for the multiple statements (that could be one or two) that point out that there's not such a thing like "identical clocks" and "same time on two clocks".

So "most" programs can ignore birth dates of people older than 52? I don't think so.

Do most programs need to know the birth date of the user?

Most of the programs I write do. Well, of people, but not typically the user.

Most programs don't deal with birth dates and people. It's like stating that most "computers" are neither on a desktop nor in a pocket. Technically correct, as counter-intuitive as it is.

I suppose it depends on if you think about a “fact month”, that is the series of days people experience, or the formal calendar months as the things being handled by the system.

The daylight savings time transition doesn’t “shorten” or “lengthen” the day, it merely transforms the clock. The day isn’t 25 hours or 23 hours. This is essentially the same thing as the Julian/Gregorian swap. The day didn’t really change, just the system we use to understand what day it is.

The span of time users experienced was weird, but this wasn’t the unit of time being shorter or longer. It’s an artifact of the transition not anything happening to the time.

A lot of these falsehoods on the list can be side stepped by distinguishing between the dimensions and the facts about representing time.

Clicking through the links, this post appears to be the source: https://news.ycombinator.com/item?id=4128470

As another commenter noted, the exception appears to be September 1752.

That's a fun example but whether it's worth worrying about is another question...

As the comments to that comment points out, 1752 is only for one specific country. All countries switched at different times (and a few even switched back and forth a few times). Greece, in particular, seems to have switched as late as 1923.

Russia is a big one too, especially for early 20th century history nerds.

They used the Julian calendar until after the Revolution, so when reading accounts of, say, most of WW1, Russian sources have dates that are 13 days off from Western sources. This leads to much confusion when authors don’t make it clear they’ve converted the dates (or not).

Amusingly, one of the first casualties of this was the October Revolution, which in the new (Gregorian) calendar actually occurred on November 7th

I'd expect in a lunar calendar system? (where 12 lunar months are to short to fill a year, and I think some of them fix this by inserting an extra half-month)

But I wish this list came with examples, and if it really means a different calendar system it's IMHO not as interesting, because it's IMHO fairly obvious that different calendar systems follow different rules. Or maybe during the switch to Gregorian calendar? That you'd at least encounter with dates for things long ago - although that transition is very "here be dragons" and very local.

Lunar month is a little over 29 days on average. And most lunar calendars do not align with solar year but rather have leap months added. E.g. Hebrew calendar [1].

[1]: https://en.wikipedia.org/wiki/Hebrew_calendar

Ok, you made me look up an example: "The Ethiopian calendar has twelve months of thirty days plus five or six epagomenal days, which comprise a thirteenth month."

https://en.wikipedia.org/wiki/Intercalation_(timekeeping)

https://en.wikipedia.org/wiki/Ethiopian_calendar

I guess its the choice if you fix the offset every year or wait until you accumulate a full month of offset.

I suppose you could have 31 days plus an hour. This depends on how you are tracking time and if that includes free-running counters.

If I am not wrong this holds true for the switch from Julian calendar to the Gregorian one. Some months were shortened to be synchronised with the new system. And if I am not mistaken Jewish and Arabs do not use the same systems we use for months and years

For an added twist this changeover occurred in different years, at different times in different countries .. and not always with the same number of days difference.

Good Times.

And even more good times. It seems sometimes some countries went back to Julian...

Others have already answered this one, but somewhat relevant: https://www.timeanddate.com/date/february-30.html

September 1752

Or October 1582, Or December 1582,

Or any of a number of different dates depending on where you were located: https://en.m.wikipedia.org/wiki/List_of_adoption_dates_of_th...

Most countries had at least one month that differed some time from 1580ish to 1800ish when they switched calenders

Don't know about more recent examples

https://en.wikipedia.org/wiki/List_of_adoption_dates_of_the_...

Actually looking at that tells me it is a mess... Like Belarus and Lithuania changing back to Julian calendar in 1800... And then again to Gregorian in 1918.

Maybe they're developing software to be used on Mars? 687 day years mentioned in Gist comments.

Ah ok cool - thanks for the replies!

So I guess its not really something that I need to worry about!

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