Implementing other Calendar system in Tiddlywiki

[Mohammad]

While Georgian calendar system is the most dominant around the word and Tiddlywiki also use it,

there are other calendar system used around the world like Jalaali (solar system), Hijri, Hebrew, Chinese and ...

see  https://en.wikipedia.org/wiki/List_of_calendars

This thread discuss the possible method to add/implement such calendar system to Tiddlywiki.

Reference: 

1. https://groups.google.com/d/msg/tiddlywiki/meN6nSlvyhw/hkOoD5W0AgAJ
   
2. https://groups.google.com/d/msg/tiddlywiki/0jIuCjeK-zA/XudxYAlLAgAJ
   

[Mohammad]

I found this page which contains useful information and code on some other Calendar system

https://www.projectpluto.com/calendar.htm#persian_diff

[Mohammad]

Example Calendar system: Persian Calendar

Like the Gregorian and Julian calendars, the Persian calendar is strictly solar in nature; that is, it matches the seasons very nicely (better, in fact, than any other calendar on these pages), but makes no real effort to reflect lunar cycles. There are twelve months per year, as follows.

farvardin (frvrdyn)     31 days
ordibehesht (ardybhSt)  31 days
khordad (Krdad)         31 days
tir (tyr)               31 days
mordad (mrdad)          31 days
shahrivar (Shryvr)      31 days
mehr (mhr)              30 days
Aban (Aban)             30 days
Azar (AZr)              30 days
day (dy)                30 days
bahman (bhmn)           30 days
esfand (asfnd)         29/30 days

The year begins at the spring equinox. If that instant is before midday, Teheran time, then that day is 1 farvardin; otherwise, the next day is 1 farvardin. This can result in either 365 or 366 days per year. In the former (usual) case, the last month of esfand has 29 days; otherwise, it has 30 days.

The Jalali calendar uses the "exact" astronomical equinox; that is to say, it's based on observations. The Modern Persian calendar instead inserts leap years algorithmically, with a complex pattern of 683 leap days inserted over a cycle of 2820 years. This actually makes the Modern Persian calendar extremely easy to program (see the source code described here.) The Jalali calendar is a little trickier, as will be discussed below.

[TiddlyTweeter]

Ciao Mohammad

I believe the Persian calendar system is likely the most astronomically accurate of currently used calendar systems.

Its based on observation, unlike Gregorian which is based on rules.

https://www.timeanddate.com/calendar/persian-calendar.html

Just a comment

TT

[TiddlyTweeter]

Ciao Mohammad

I think this is a fascinating topic where computer science meets social behaviour. A little while ago there was a related interesting thread ... https://groups.google.com/d/msg/tiddlywiki/YaFzHXfjnFc/Rhkybx0BAQAJ

That thread was concerned with date RANGES in TW standard date mechanism (it only works from 1899 11 30 00:00:00.00 on in Gregorian).

Regarding your OP, its worth mentioning that accurate  historical dating that goes back a long, long way is more needed by astronomers than historians or social scientists.

The modern concept of date recording becomes less workable the further you go back in time. In pre-industrial revolution societies every century back "universal" dates become rarer. Mainly used on official documents. Otherwise date recording conforms more to local perception of agricultural peasants--I.e. based on empirical observation of crop cycles.

The meaning here is: better dating in TW would be good but only necessary back far enough with accuracy for practical aims. 

Just comments.

TT

Regarding

[Mohammad]

Hi Josiah,

On Monday, April 13, 2020 at 11:09:42 AM UTC+4:30, TiddlyTweeter wrote:

Ciao Mohammad

I believe the Persian calendar system is likely the most astronomically accurate of currently used calendar systems.

That's true the first day of new year is exactly the first day of spring!

[Mohammad]

Thanks Josiah for these informative comments!