cal-persia.el disagrees with Iranian calendar in A.D. 2025

Roozbeh Pournader roozbeh at
Tue Apr 5 16:14:20 UTC 2005

On Thu, 2005-03-31 at 02:18 -0500, Paul Eggert wrote:
> Ed Reingold <reingold at> writes:
> > For the TZ data base, what is the point of making one assumption over the 
> > other?  Neither will be known right or wrong for another 20 years.
> By the way, in researching this I found the following reference useful:
>   M. Heydari-Malayeri (Paris Observatory),
>   A concise review of the Iranian calendar (2005-02-15),
>   <>
> It mentions the March 20, 2025 discrepancy, and it has some
> interesting and not-altogether-positive things to say about the method
> used in GNU Emacs.  I hadn't realized how controversial this area is.

The issue is only controversial in academic circles. It's not
controversial in legal circles at all. The text of the Iranian law, in
effect since 1925, clearly mentions that the true solar year is the
measure, and there is no arithmetic leap year calculation involved.

There has never been any serious plan to change that law, and since the
original law is passed by the Majlis (parliament), there are only two
ways to change it:

1) The Guardian Council calling it void because of it being against
Islam or the Islamic Republic Constitution, which would be a really
weird thing to do, since it's Islamic (uses the year of Hegira of
Muhammed as its first year), and the calendar being "hejri-e
shamsi" (Solar Hegira-based) is mentioned in the Islamic Constitution.

2) The Majlis replacing it with a new law, which is again very
improbable since: a) almost every calendar authority believes that one
should stick to such an "accurate" calendar. This is based on my
discussions with both the current calendar authority (the High Council
of Calendar, appointed by Tehran University and empowered by the Board
of Ministers), and the previous one (Dr Iraj Malekpour, same appointment
and empowerment). b) It's very improbable that a majority of the Iranian
Majlis will even understand any proposal (or importance of such a
proposal) to adopt an arithmetic Persian calendar, specially since the
real difference is very rare. And c) Iranians traditionally celebrate
the moment of vernal equinox as the beginning of the new Persian year.

(Please understand that I am personally among the supporters of an
arithmetic Persian calendar.)

> Thanks for clarifying this.  Would it be appropriate to make the
> following change to the GNU Emacs user documentation, if only to help
> forestall future bug reports in this area?

I really believe that the suggested change in GNU Emacs is fine, but one
should correct that single instance in tzdata and mention that an
astronomical calendar is practically used.

I'm not sure about Birashk's suggested leap year rule (which is based on
the wrong and overly simplistic assumptions that the average length of
the spring equinoctial year is the same as the average tropical year,
that the average will remain the same forever, and that the length of an
astronomical day is constant), but a very simpler one I checked (using
33-year cycles) will not differ from the astronomical one until sometime
in the 2070s.



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