Time zone rules change

Hammad Hassan-WHH011 WHH011 at motorola.com
Sun Sep 17 06:26:35 UTC 2006

Hi Paul,
The changes will be at the midnight of Sep 24 0:00, when we reach 1:00AM at Sep 25 the clocks will be turned back to 12:00AM. I think also this change will be this year and may be the next couple of years only (They just want to exclude Ramadan from the summer time, if So - the change will be among 3 years only if my calculations is correct), Certainly we can't depend on the lunar system.

Hassan Hammad

-----Original Message-----
From: Paul Eggert [mailto:eggert at CS.UCLA.EDU] 
Sent: Thursday, September 14, 2006 8:03 PM
To: tz at elsie.nci.nih.gov
Cc: Hammad Hassan-WHH011
Subject: Re: Time zone rules change

Jesper Norgaard Welen <jnorgard at prodigy.net.mx> writes:

> the article says that Ramadan presumably will start the 24.th. of 
> September 2006, and on the eve of that day, they will switch back to 
> winter time.  The rule change should therefore be  Sep 25 0:00.

and "Paul Schauble" <Paul.Schauble at ticketmaster.com> writes:

> It may not be midnight. Some Middle Eastern countries have the next 
> day starting at sunset.

"Christmas Eve" is the day before Christmas, and that's how I interpreted that story's "eve".  I chose midnight since our DB has previous-year changes at midnight.  If the change is Sept 25 00:00 rather than Sept 24 00:00, or is at some other time than 00:00, I hope Hammad Hassan will correct us.

Robert Elz <kre at munnari.oz.au> writes:

> it is pretty clear that the "eve of Ramadan" rule for ending summer 
> time won't last past the next few years, 2011 at the latest I'd guess, 
> but perhaps more likely just this year and the next couple,

My guess was different: that it affects only this year, because the otherwise-as-usual change directly interferes with the preparation for the start of Ramadan this year, but wouldn't in other years.  It's just a guess of course.

Oscar van Vlijmen <ovv at hetnet.nl> writes:

> (My calculations, based on Reingold/Dershowitz "Calendrical Calculations"
> algorithms).

I came up with the same results that you did.  Here's the source code to my calculations, in GNU Emacs Lisp (tested under version 21.4).
The output is text that you can feed directly to zic.

   (defun generate-ramadan ()
     (let ((year 1427))
       (while (< year (+ 1427 33))
         (let ((date (calendar-gregorian-from-absolute
                      (calendar-absolute-from-islamic (list 9 1 year)))))
           (insert (format "Rule\tEgypt\t%d\tonly\t-\t%s\t%d\t 0:00\t0\t-\n"
                           (extract-calendar-year date)
                           (calendar-month-name (extract-calendar-month date) 3)
                           (extract-calendar-day date))))
         (setq year (1+ year)))))

I came to the same conclusion that you did, which is that a lunar calendar is not likely to be the basis of a daylight saving scheme.
(Though it might be the basis of a _moonlight_ saving scheme, for those of us who admire moonlight!)

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