[TUHS] History of cal(1)?

[Bakul Shah via TUHS]

Things get quite complicated when you have lunisolar calendars!
An extra lunar month is added every 32 or 33 lunar months to sync
up with the solar cycle[1]. In India they have been in use for
many centuries and even today most religious festivals and events
follow them. Here's a typical calendar page[2]:

https://www.prokerala.com/general/calendar/hinducalendar.php?year=2025&mon=september&sb=1#calendar

As you can see plenty of information is imparted[3]. When I was
a kid, we would always get a day-per-page calendar every year
because of this.


[1] One's birthday as per Indian & Greorian calendars lines up almost
    exactly every 19 years.
[2] Not sure what software they use. The calendar also changes based
    on your location!
[3] Things like sunrise/sunset, the zodiac moon is passing through,
    etc. Details explained here:
      https://www.anaadi.org/post/indian-calendar-part-3-the-panchangam

> On Sep 22, 2025, at 6:50 PM, Rob Pike via TUHS <tuhs at tuhs.org> wrote:
> 
> There are so many calendars in the world. The Muslim calendar. The Jewish
> calendar. The Mayan calendar. Countless indigenous calendars too, I am
> certain.
> 
> Whenever computing butts up against real human culture, things get messy
> fast. No point in trying to catalog the mess exhaustively.
> 
> -rob
> 
> 
> On Tue, Sep 23, 2025 at 11:14 AM Steffen Nurpmeso via TUHS <tuhs at tuhs.org>
> wrote:
> 
>> John Levine via TUHS wrote in
>> <20250923003454.03671DD56E9A at ary.qy>:
>> |It appears that Douglas McIlroy via TUHS <douglas.mcilroy at dartmouth.edu>
>> \
>> |said:
>> |>> [cal(1)] has all the logic to adjust for 16th century
>> |>> calendar changes ...  (Try "cal 9 1752")
>> |>> My impression is that [it is] overimplemented.
>> |>
>> |>The fact that a 16th century change is illustrated by an 18th century
>> |>example suggests that not quite "all the logic" is there. It's good
>> |>for Great Britain and its colonies, but not elsewhere. So I'd say it's
>> |>underimplemented :)
>> |
>> |You'll be relieved to know that ncal has addressed that omission:
>> |
>> |$ ncal -p
>> | AL Albania        1912-11-30      IS Iceland        1700-11-16
>> | AT Austria        1583-10-05      IT Italy          1582-10-04
>> | AU Australia      1752-09-02      JP Japan          1918-12-18
>> | BE Belgium        1582-12-14      LT Lithuania      1918-02-01
>> | BG Bulgaria       1916-03-31      LU Luxembourg     1582-12-14
>> | CA Canada         1752-09-02      LV Latvia         1918-02-01
>> | CH Switzerland    1655-02-28      NL Netherlands    1582-12-14
>> | CN China          1911-12-18      NO Norway         1700-02-18
>> | CZ Czech Republic 1584-01-06      PL Poland         1582-10-04
>> | DE Germany        1700-02-18      PT Portugal       1582-10-04
>> 
>> (In an earlier thread on this topic Mr. McIlroy threw into
>> the discussion that for example Germany was very much more
>> complicated than that.  And i said iirc something like "we
>> tried to keep it local by then" [actually notoriously so], and
>> unfortunately talked about Mors Teutonicus even, as "we more
>> usually than not reached the Holy Land" before reaching the holy
>> land, which *possibly* is the only one and true way to reach the
>> holy land .. if you can.  (Pffffhh, what a talk.))
>> 
>> | DK Denmark        1700-02-18      RO Romania        1919-03-31
>> | ES Spain          1582-10-04      RU Russia         1918-01-31
>> | FI Finland        1753-02-17      SI Slovenia       1919-03-04
>> | FR France         1582-12-09      SE Sweden         1753-02-17
>> | GB United Kingdom 1752-09-02      TR Turkey         1926-12-18
>> | GR Greece         1924-03-09     *US United States  1752-09-02
>> | HU Hungary        1587-10-21      YU Yugoslavia     1919-03-04
>> |
>> |R's,
>> |John
>> |
>> |PS: my point was not that it's a lot of code, but that is's a
>> distinctive \
>> |hack so one might
>> |look at earlier calendar programs to see whether they also did it to \
>> |try and trace the
>> |chain of influence.
>> --End of <20250923003454.03671DD56E9A at ary.qy>
>> 
>> --steffen
>> |
>> |Der Kragenbaer,                The moon bear,
>> |der holt sich munter           he cheerfully and one by one
>> |einen nach dem anderen runter  wa.ks himself off
>> |(By Robert Gernhardt)
>>