Editing Islamic calendar (section)

==Calculated Islamic calendars==
===Islamic calendar of Turkey===
Turkish Muslims use an Islamic calendar which is calculated several years in advance by the [[Presidency of Religious Affairs|Turkish Presidency of Religious Affairs]] (Diyanet İşleri Başkanlığı). From 1 Muharrem 1400 AH (21 November 1979) until 29 Zilhicce 1435 (24 October 2014) the computed Turkish lunar calendar was based on the following rule: "The lunar month is assumed to begin on the evening when, within some region of the terrestrial globe, the computed centre of the lunar crescent at local sunset is more than 5° above the local horizon and (geocentrically) more than 8° from the Sun." In the current rule the (computed) lunar crescent has to be above the local horizon of [[Ankara]] at sunset.<ref name=turkey>{{cite web |url=https://webspace.science.uu.nl/~gent0113/islam/diyanetcalendar.htm |title=The Islamic Calendar of Turkey |work=[[Mathematical Institute]] |publisher=[[Utrecht University]] |access-date=4 February 2021 |date=April 2021 |first=R.H. |last=van Gent |archive-date=31 January 2021 |archive-url=https://web.archive.org/web/20210131000244/https://webspace.science.uu.nl/~gent0113/islam/diyanetcalendar.htm |url-status=live }}</ref>

===Saudi Arabia's ''Umm al-Qura'' calendar===
Saudi Arabia has traditionally used the Umm al-Qura calendar, which is based on astronomical calculations, for administrative purposes. The parameters used in the establishment of this calendar underwent significant changes during the decade to AH 1423.<ref>{{cite web |url=http://www.icoproject.org/pdf/khan_2001.pdf |title=Crescent sighting using the Uml al Qura calendar in Saudi Arabia To Determine Ramadan And Eid Ul Fitir Of 1422 AH And Its Implications For Unity In Different Countries By Dr. Muhammad M H Khan |archive-url=https://web.archive.org/web/20060515093842/http://www.icoproject.org/pdf/khan_2001.pdf |archive-date=15 May 2006 |year=2001 |access-date=4 February 2022 |work=Ico Project}}</ref><ref>{{cite web |url=https://webspace.science.uu.nl/~gent0113/islam/ummalqura.htm |title=The Umm al-Qura Calendar of Saudi Arabia |work=[[Mathematical Institute]] |publisher=[[Utrecht University]] |first=R.H. |last=van Gent |date=April 2021 |access-date=4 February 2022 |archive-date=11 June 2011 |archive-url=https://web.archive.org/web/20110611040922/http://www.staff.science.uu.nl/~gent0113/islam/ummalqura.htm |url-status=live }}</ref>

Before AH 1420 (before 18 April 1999), if the moon's age at sunset in [[Riyadh]] was at least 12 hours, then the day ''ending'' at that sunset was the first day of the month. This often caused the Saudis to celebrate holy days one or even two days before other predominantly Muslim countries, including the dates for the Hajj, which can only be dated using Saudi dates because it is performed in Mecca.

From AH 1420–22, if moonset occurred after sunset at Mecca, then the day beginning at that sunset was the first day of a Saudi month, essentially the same rule used by Malaysia, Indonesia, and others (except for the location from which the ''hilal'' was observed).

Since the beginning of AH 1423 (16 March 2002), the rule has been clarified a little by requiring the geocentric conjunction of the sun and moon to occur before sunset, in addition to requiring moonset to occur after sunset at Mecca. This ensures that the moon has moved past the sun by sunset, even though the sky may still be too bright immediately before moonset to actually see the crescent.

In 2007, the [[Islamic Society of North America]], the ''Fiqh'' Council of North America and the European Council for ''[[Fatwa]]'' and Research announced that they would henceforth use a calendar based on calculations using the same parameters as the ''Umm al-Qura'' calendar to determine (well in advance) the beginning of all lunar months (and therefore the days associated with all religious observances). This was intended as a first step on the way to unify, at some future time, Muslims' calendars throughout the world.<ref>{{cite web |url=http://tabsir.net/?p=621#more-621 |website=tabsir.net |title=Can the Umm al Qura calendar serve as a global Islamic calendar? |first=Khalid |last=Chraibi |date=23 July 2008 |access-date=4 February 2022 |publisher=[[WordPress]] |archive-date=8 March 2022 |archive-url=https://web.archive.org/web/20220308190450/http://tabsir.net/?p=621#more-621 |url-status=live }}</ref>

On 14 February 2016, Saudi Arabia [[adoption of the Gregorian calendar|adopted the Gregorian calendar]] for payment of the monthly salaries of government employees (as a cost cutting measure),<ref>{{cite news |url=https://www.dw.com/en/saudi-arabia-switches-to-western-calendar/a-35942460 |title=Saudi Arabia trims expenses and work days |date=10 February 2016 |access-date=15 January 2023 |work=[[DW News]] |publisher=[[Deutsche Welle]] |archive-date=16 January 2023 |archive-url=https://web.archive.org/web/20230116104948/https://www.dw.com/en/saudi-arabia-switches-to-western-calendar/a-35942460 |url-status=live }}</ref> while retaining the Islamic calendar for religious purposes.<ref name=Economist171216>{{cite news |url=https://www.economist.com/news/middle-east-and-africa/21711938-hauling-saudi-arabia-21st-century-saudi-arabia-adopts-gregorian |title=The prince's time machine: Saudi Arabia adopts the Gregorian calendar |newspaper=[[The Economist]] |date=17 December 2016 |access-date=4 February 2022 |publisher=[[The Economist Newspaper Limited]] |archive-date=14 October 2017 |archive-url=https://web.archive.org/web/20171014042857/https://www.economist.com/news/middle-east-and-africa/21711938-hauling-saudi-arabia-21st-century-saudi-arabia-adopts-gregorian |url-status=live }}</ref>