From tcarey@bluetrain.com Tue Aug 15 12:22:31 2000
From: Thomas Carey <tcarey@bluetrain.com>
To: tz@iana.org
Subject: easy question: when dst transition occurs at 00:00 hours...
Date: Tue, 15 Aug 2000 09:24:39 -0700
Message-ID: <633420008215162439171@bluetrain.com>
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many locales undergo DST transition at midnight - for instance - on Thu 21
Sept 2000 19:30 - DST will end in Tehran, and local time will go from
00:00->23:00 (actually, from 23:59 to 23:00). My question is whether this
extra hour occurs (locally) on thursday or friday. I'd assume thursday, as
00:00 doesn't arrive before the transition.

can anyone confirm?

thanks
tc


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From alex@agsm.edu.au Tue Aug 15 20:39:53 2000
From: Alex LIVINGSTON <alex@agsm.edu.au>
To: tz@iana.org
Subject: Re: easy question: when dst transition occurs at 00:00 hours...
Date: Wed, 16 Aug 2000 10:39:38 +1000
Message-ID: <a04320404b5bf8f955eba@[149.171.217.233]>
In-Reply-To: <633420008215162439171@bluetrain.com>
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At 09:24 -0700 2000-08-15, Thomas Carey wrote:
>many locales undergo DST transition at midnight - for instance - on Thu 21
>Sept 2000 19:30 - DST will end in Tehran, and local time will go from
>00:00->23:00 (actually, from 23:59 to 23:00).

If "00:00 to 23:00" seems odd, you can say "24:00 to 23:00" - the 
change doesn't take a minute, it happens instantaneously. But just 
what time is it at that instant? Is that defined anywhere?

>My question is whether this
>extra hour occurs (locally) on thursday or friday. I'd assume thursday, as
>00:00 doesn't arrive before the transition.
>
>can anyone confirm?

I can't confirm, but to me it would seem far stranger and more 
confusing to have  periods from 23:00 to 24:00 both at the beginning 
and the end of the same day, than to have two lots of 23:00 to 24:00 
consecutively within the same day. (I'm ignoring the question of the 
inclusivity or otherwise of the beginning and end instants of these 
periods.)

--Alex
-- 
_______________
Alex LIVINGSTON
Macintosh and Lotus Notes Support / Information Technology (IT)
Australian Graduate School of Management (AGSM)
UNSW SYDNEY NSW 2052 / Australia

Facsimile: +61 2 9931-9349 / Telephone: +61 2 9931-9264
Time     : UTC+11---[last Mar. Sun.---UTC+10---[last Aug. Sun.---UTC+11---

At midday today, Wednesday, August 16,
   time since epoch (1-1-1 at 00:00:00) is
     730347.5 days = 1999.62353779 average Gregorian years
   time until 3rd millennium, 21st century, 201st decade, 2001st year is
     137.5 days = .37646221 average Gregorian years

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From ephraim@cs.huji.ac.il Wed Aug 16 11:30:18 2000
From: Ephraim Silverberg <ephraim@cs.huji.ac.il>
To: tz@iana.org
Subject: Re: easy question: when dst transition occurs at 00:00 hours...
Date: Wed, 16 Aug 2000 18:30:10 +0300
Message-ID:
 <Pine.SGI.4.20_heb2.08.0008161825250.25881-100000@kubbe.cs.huji.ac.il>
In-Reply-To: <633420008215162439171@bluetrain.com>
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On Tue, 15 Aug 2000, Thomas Carey wrote:

> many locales undergo DST transition at midnight - for instance - on Thu 21
> Sept 2000 19:30 - DST will end in Tehran, and local time will go from
> 00:00->23:00 (actually, from 23:59 to 23:00). My question is whether this
> extra hour occurs (locally) on thursday or friday. I'd assume thursday, as
> 00:00 doesn't arrive before the transition.

Before 1999, Israel used to change back to standard time at 00:00 (usually
on a Saturday night) and this caused massive confusion since there were two
23:00 - 00:00 hours that night.

In 1999, at the request of the Airport Authority the time change took place
at 02:00 old time to avoid this confusion and having people miss flights
because of this.

>From 2000 onwards, the change back is slated to take place at 01:00 (why
this was changed from 02:00 is beyond me).

Ephraim
___________________________________________________________________________
Ephraim Silverberg, CSE System Group,        Phone number:    972-2-6585521
Hebrew University, Jerusalem, Israel.        Fax number:      972-2-6585439
WWW: http://www.cs.huji.ac.il/~ephraim       E-mail: ephraim@cse.huji.ac.il


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