MUHAMMADIYAH.OR.ID, YOGYAKARTA—Surah Saba verse 28 and Al-Anbya verse 107 mention that Islam is a religion for the whole world. The verses indicate it’s necessary to have one worldwide applicable Islamic calendar. A zonal calendar dividing the earth into several parts contradicts the universality of Islam. Globalized Muslims need a time system that can apply to all regions worldwide.
In the Eid al-Fitr gathering conducted by the Central Board of Muhammadiyah at Universitas Muhammadiyah Yogyakarta (UMY) on Sunday (30/4), the Chairman of Muhammadiyah Syamsul Anwar affirmed the urgency of a global Islamic calendar. Abu Hurairah narrated that the Prophet said: “The fast is the day the people fast, the breaking of the fast is the day the people break their fast, and the sacrifice is the day the people sacrifice” (at-Tirmidzi, al-Baihaqi, ad-Daraquthni, and Abu Dawud).
The hadith mentions “people”, a plural noun. It means that the fast, Eid al-Fitr, and Eid al-Adha are performed on a day simultaneously. It will be possible if there is a global Islamic calendar.
Several Shafi’i scholars mentioned, “The method of rukyat (sighting of the moon) in a place applies to all people in the globe” (an-Nawawī, Syarḥ Ṣahiḥ Muslim, VII: 197). Meanwhile, a Hanafi scholar said that, when the crescent exists, all people must fast wherever they are. It’s obligatory for people in the East to fast due to the sighting of the moon by the people in the West, according to the Hanafi school of thought.

Principles of the Global Islamic Calendar.
Syamsul mentioned five principles of a global Islamic calendar.
First, the global Islamic calendar uses the method of hisab (an astronomical calculation). It cannot be created by the method of rukyat.
Second, there should be a transfer of imkan rukyat. The crescent moon cannot be sighted all around the world concurrently. Thus, imkanu rukyat in a place represents other places where it has not happened yet.
Third, the earth is seen as one matlak. It is a consequence of transferring imkanu rukyat. Therefore, imkanu rukyat in a place applies to all areas in the world because the earth is viewed as one matlak.
Fourth, there is the synchronization of the day and date worldwide. This means that there is only one date and one day all over the world.
Fifth, the global Islamic calendar refers to the International Date Line (IDL). It is an internationally accepted demarcation of the surface of earth, running between the south and north poles and serving as the boundary between one calendar day and the next. It passes through the Pacific Ocean, roughly following the 180.0° line of longitude and deviating to pass around some territories and island groups. Crossing the date line eastbound decreases the date by one day, while crossing the date line westbound increases the date.

The Use of the Rukyat Method Hinders the Global Islamic Calendar
It is highly improbable to manage time by observing the crescent moon (the method of rukyat). The scope of this method is limited to specific geographic locations on the first day of the moon’s visibility. It results differences in the Hijri date in various places.

Furthermore, the use of rukyat cannot unify Islamic holidays worldwide, nor can it predictively arrange the timing system for the future or past. This condition has serious consequences, as for 1500 years, Islam has yet had an integrated comprehensive Islamic calendar.
Indeed, the result of the method of rukyat cannot apply to the entire world, particularly when the crescent moon is visible in certain areas. While the crescent may be visible in one area, it may be invisible in other areas and may still be below the horizon in some places. The crescent moon cannot be sighted globally on the same evening, so it yields discrepancies in the beginning of the Islamic month.