On Tue, 2005-04-05 at 15:02 -0700, Paul Eggert wrote:

...

This suggests that cal-persia.el could be changed as well, as its practical use is (I think) for predicting dates in Iran. I'm hesitant to propose a change myself, though, as I'm not an expert in either the calendar or the code.

Ed could probably help with that... I don't know any LISP, and every useful thing I know about computing astronomical calendars comes from his book.

As I have said before, the mechanisms needed to do the Persian astronomical calendar are not in the existing Emacs code; the algorithms in my Calendrical Calculations will never be released under the GNU license, so somebody would have to come up with entirely new algorithms and implement them in Emacs-Lisp. As it stands, the arithmetical Persian calendar is an excellent approximation to the astronomical version--a much better approximation than the GNU Emacs arithmetic approximation to the Islamic calendar is to the true observational Islamic calendar. I don't see any reasonable changes to cal-persia.el as being needed. The documentation could be modified to state that the calendar as implemented is a close approximation to the astronomical version. I leave that up to others.