Ummul Qura Calendar of Saudi Arabia
Ummul Qura Calendar is a civil islamic calendrical system used in Saudi Arabia. But this hijri calendar is used and referenced by many more muslim countries.
In the past, there had been controversies regarding this calendar. Many of them centraled on the discrepancy of the beginning of the month and the calculated position of the crescent (or new moon) at sunset in Makkah. It was not uncommon that the new month begins although astronomically the moon already sets before the sun sets. Another source of the controversy was the obscure nature of the rules used to design or to determine the dates in the calendar.
Such noted problems were becoming global muslim community concerns especially during the determination of religiously important dates for Eids, Ramadan and Hajj. And many astronomers
Since recently, however, the authority behind the Ummul Qura Calendar had proposed a new rule in determining the beginning of islamic hijri months. This new rule is regarded as astronomically sound in making sure that after conjunction the moon is above the horizon and sets after the sun as seen from Makkah, Saudi Arabia.
However, for the determination of the beginning of religiously related months such as Ramadan, Shawwal and Dhulqaida, the government of Saudi Arabia often changes the date according to moon sighting reports (or claims).
See islamic calendar and important dates based on Ummul Qura system:
You may also download the calendar from the pages linked above. If available, the PDFs of the calendar can be downloaded or printed.