Re: [Tzdist] Fun with tzdata and non-Gregorian DST rules

Ken Murchison <murch@andrew.cmu.edu> Sat, 14 November 2015 01:59 UTC

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Date: Fri, 13 Nov 2015 20:58:57 -0500
From: Ken Murchison <murch@andrew.cmu.edu>
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Cc: Time Zone Data Distribution Service <tzdist@ietf.org>
Subject: Re: [Tzdist] Fun with tzdata and non-Gregorian DST rules
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On 11/13/2015 02:41 PM, Jonathan Lennox wrote:
> On Friday, November 13 2015, "Ken Murchison" wrote to "Time Zone Data Distribution Service" saying:
>
>> I briefly looked for other zones based on lunisolar calendars and didn't come
>> up with any.  The Brazilian rules are essentially based around Easter and
>> there is no way that I have found to represent Easter as a recurrence rule in
>> iCalendar.
> Between 2005 and 2012, Israeli daylight savings time (Asia/Jerusalem) ended
> on the Hebrew calendar, which is lunisolar: the rule was that DST ended on
> the Saturday before Yom Kippur (the 10th of Tishrei).  (It started on the
> Gregorian calendar, on the Friday before April 2nd.)
>
> The law was changed in 2013, but this still seems like something you could
> try modeling with RSCALE, either for the historical period or for a
> proleptic version of the 2005 rules.

https://cyrus-test.andrew.cmu.edu/tzdist/zones/Asia/Jerusalem_Hebrew

The rule for end of DST for 2005-1012 is this:

BEGIN:STANDARD
TZNAME:IST
TZOFFSETFROM:+0300
TZOFFSETTO:+0200
DTSTART:20051009T020000
RRULE:FREQ=YEARLY;RSCALE=HEBREW;BYMONTH=1;BYMONTHDAY=3,4,5,6,7,8,9;BYDAY=SU;UNTIL=20120923T010000Z
END:STANDARD

Its also looks like 6 of the 8 transitions from 2001 to 2004 are based 
on a fixed date on the Hebrew calendar: 16 Nisan and 7 Tishrei

-- 
Kenneth Murchison
Principal Systems Software Engineer
Carnegie Mellon University