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- To: developer at arabeyes dot org
- Subject: Re: FreeHijri
- From: "Youcef Rabah Rahal" <yrrahal42 at hotmail dot com>
- Date: Mon, 09 Jun 2003 14:21:03 +0200
From: Roozbeh Pournader
CC: Behdad Esfahbod
Date: Tue, 27 May 2003 22:13:34 +0430 (IRST)
Today, me and Behdad were trying to develop a sane, realistic, and
implementable model for a Lunar Islamic or Hijri calendar library, and we
came to some general ideas to make it *really work*.
First of all, let me tell you about the real problems:
1) The Hijri calendar is based on the location of the reference point on
the Earth. So we can't have a single calendar for everybody on Earth.
Normally, a single calendar is possible, there is only the line of date
that'd make Earth split into 2 regions, similar to the one of the gregorian
which is fixed somewhere in the pacific ocean and which makes the same
region to have a
difference of 24 hours (fortunately this line is in the pacific, so there
are not many people
suffering from this thing :-). The Lunar calendar's line is of course not
In the case of the Lunar calandar, this line is straight forward. It should
separate the countries
where the new cresecnt is visible and in which Ramadhan starts for ex; from
countries which are at the east of them and which should make Shaaban 30
What is absolutely illogical, is that sometime an Islamic Country starts
and the one at its west is still in Shaaban !
2) A single country needs a single fixed calendar for its official
and the usually-nationwide festivites, and because of the possiblity for
moon being visible in certain parts of a country but not in the others,
central authority in each government or country needs to determine and
announce the official starting days of Lunar months, and most
specifically Ramadan and Shawwal.
3) Because of the importance of the general stability of the calendar,
and specially for being able to predetermine the holidays, all Islamic
countries have a civil calendar, using different algorithms (either
computational or astronomical) for pre-determining the starting days of
all of the months of the year. That calendar is then published before
the beginning of the year on paper, and then all the citizens can use
4) But because of the very special importance of Ramadan and Shawwal in
Muslim fasting, in most of the Islamic countries the starting days of
these two are observed based on actually seeing the moon crescent, not
relying on the computational or the astronomical algorithm. Different
Islamic countries have different religious or civil laws for determining
those, and sometimes the authority for publishing the pre-computed
calendar is different from the authority for announcing the starting
days of Ramadan and Shawwal. Sometimes, one of these authorities,
specially the first, may change without previous notice.
5) All of that makes implementing a worldwide Hijri calendar really
I mostly agree here (points 2 to 5). However, I am (personally) for a
calendar that should be followed
in all Islamic countries, a calendar that is to be determined by the High
Islamic Council for example.
But I think I am talking about utopy here, so back to realism :)
What we were thinking about, is starting a general Hijri library project,
that is able to help determining the real date actually used at a certain
moment in each Islamic country.
Well, I don't know if you are aware about the Islamic Tools Library
developed by Yousef Al Harthi ?
Maybe a collaboration could be envisioned ? (just a thought,
because your project seems kind of different from ITL)
We have some broad ideas on how to maintain the library, since it will be
*hard* to do that, and that will need many volunteers from different
countries for at least providing the data, and updating it on-time.
But technically, and from a developer point of view, it will work this
1) We will use the publicly available algorithms for computing the
calendars. A good reference for the algorithm to use will be the ones
available in the book "Calendrical Calculations: The Millennium Edition"
by Edward M. Reingold and Nachum Dershowitz. The algorithms in that book
are already implemented in GNU Emacs.
2) Since each country will have a different situation (like civil calendar
vs astronomical calendar), the exact situation of each country with an
official Lunar calendar will be specified in data files, that will include
things like the exact position of the reference point of the country on
Earth, its height, its timezone, which kind of algorithm it uses, ...
The data will be updated based on more available information.
3) For countries that observe the moon crescent officially, there will be
a central database of starting days of such Hijri months in Gregorian
dates, based on the announcements of the authority. The calendar computing
software will have a daemon that automatically fetches and updates this
data file frequently, and most importantly on certain dates like the
ending days of Sha'ban and Ramadan. This table will be in a certain
format, to be usable by different
We restate that we're not looking at the human parts of the work yet, and
what a huge effort it will need to be updated regularly and ontime. But we
guess this is the only way to have a working and minimally-maintained
Hijri calendar on each and every Free Software desktop.
Well, I am interested to give a hand. I actually study Astrophysics, but I
have no real
experience with calendars, which is a whole and a huge subject by itself.
Maybe some more details about the implementation are needed (and the human
part) (or a first shot ?).
Pro ou perso, toutes les adresses et numéros de tél que vous cherchez