[tz] FW: [Ext] The TZ Coordination

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Sun May 31 21:53:06 UTC 2020

There is also the Eid al-Fitr festival at the start of the next month Shawwal
which may last from 1-5 days, during which for some reason they typically also
do not want a time change, although I would think that an opportune period.

On 2020-05-31 12:57, Milamber wrote:
> On 5/31/20 6:25 PM, Matt Johnson-Pint wrote:
>> Forgive me if this is in any way ignorant, but why must the DST transitions
>> align so precisely with Ramadan? 

> Because, during the Ramadan, the Muslims don't eat/drink from the sunrise to the
> sundown, so in Morocco with a GMT+1 timezone, the first lunch of the day will be
> near 08:30 pm (named 'Ftour' - Breakfast). So the people (and government) prefer
> switch back to GMT+0 to have the first lunch earlier during this month.

>> Would it not be sufficient if the dates for the time change were predictable
>> as long as the switch to GMT occurred sometime before the start of Ramadan and
>> the switch back to GMT+1 occurred sometime after?  Is there a political,
>> social, or religious reason why they must be so exactly aligned?

>> On Sunday, May 31, 2020 7:03:50 AM, Milamber wrote:
>> On 5/31/20 12:09 PM, Florian Weimer wrote:
>>>> On 5/30/20 7:00 AM, Florian Weimer wrote:
>>>>>> Would this be a good opportunity to engage with the government of Morocco
>>>>>> to encourage them to give more warning?
>>>>> My understanding is that at present, they don't know themselves in
>>>>> advance.
>>>> Yes, I think you're right.
>>>>> They would have to redefine the criteria to something based
>>>>> exclusively on astronomical calculations
>>>> That shouldn't be necessary, as they're using a conservative
>>>> approximation; that is, it's OK if their approximation is a bit off
>>>> because all they need to do is to bracket the actual Ramadan rather
>>>> than predict its Gregorian dates exactly.  If they had an algorithm
>>>> they could publish it and we could use it. And it would be
>>>> technically feasible for them to have an algorithm; see the
>>>> Morocco-prediction code in the tzdb 'africa' file for an example
>>>> algorithm.
>>> It looks like the algorithm predicted correctly the data of Eid
>>> al-Fitr as 24 May, but the derivation of the end date from that is
>>> suspicious.  I think it would make more sense if the time change does
>>> not happen on Eid itself. 
>> In Morocco (where I live), the end of Ramadan (arabic month) is follow by the
>> Eid al-Fitr, and concretely it's 1 or 2 day off for the people (with
>> traditional visiting of family, big lunches/diners, etc.). So for this year
>> the astronomical calculations don't include the following 2 day off in the
>> calc. This 2 days have fall in a Sunday/Monday, so it's not acceptable by
>> people to have a time shift during these 2 day off.
>> Perhaps, you can modify the (predict) rules for next years : if the end of
>> Ramadan is a (probable) Friday or Saturday (and so the 2 day off is on a
>> weekend), the next time shift will be the next weekend.
>>>  A rule like this would ensure that Eid
>>> still uses the same time as Ramadan in every year, which is likely
>>> what people expect.

Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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