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On 08/12/2022 23:13, Toki wrote:

When LibreOffice converts Gregorian to/from Islamic Calendar dates,
when does it assume that the new Islamic day begins:
* Sunset;
* Midnight;
* Sunrise;

When LibreOffice converts Gregorian to/from Islamic Calendar dates,
when does it assume that the first of the Islamic month begins:
* Sunset;
* Midnight;
* Sunrise;

I'm completely ignorant in this area but find the questions
interesting. However, doesn't the second (on first principles) follow
from the first?

In Islam:
* The new day begins at sunset.
* The new month begins at sunrise, after the new moon has been sighted.

Judaism, is slightly more logical. Both the new day and new month begin at sunset. The new month begins on the sunset of the day that the new moon was sighted.

By way of example.
Sunset is at 5:00 PM  on Thursday.
The New moon is sighted at 5:10 PM on Thursday.
In Islam, the first of the month starts at sunrise on Friday.
In Judaism, the first of the month starts at sunset on Friday.
(If you want to be technical, replace _Judaism_ with _Karaite Judaism_.)

The western Christian calendar is also based on the start of the day is at sunset.  At this time of year this is important as it means Christmas day starts at sunset on the 24th December.  This means that twelfth night is the night starting at sunset on the 4th of January so technically Christmas finishes at sunset on the Fifth January and this is then the start of Epiphany, the period to celebrate the arrival of the 3 kings. It explains why there is a discussion each year about when you should take down the Christmas decorations. :)

Easter also has similar rules. Which is that Easter is the Saturday night/Sunday after the spring Equinox after a full Moon. Passover uses the same rule but for Friday Night, which means occasionally they a  month apart.

Calendars are just such fun.
Not sure when the next leap second is?


Cheers Ian Mac

When going through journals of pious Muslims, you will occasionally see dates like 30 Shaʿbān 12th hour immediately followed by 1 Ramaḍān 13th hour.The first through twelfth hour doesn't exist for 1 Ramadan. This is why knowing what assumptions are made about the converted date are important.

I'm completely ignorant too. A quick search leads to the further question: which islamic calendar?

As best as I can determine, LibO uses a theoretical calendar.


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