Please correct me if I'm wrong, but my understanding was that GP is partially correct, in that the lunar sighting is not an individual thing, but done at the communal level by the central authority. It's just that like most religions, Islam has multiple streams, and this there are multiple central authorities.
Is this not how it works? I'm not Muslim, this is what I understood from a Muslim coworker. He also implied that there's some politics involved, in that various Middle Eastern countries align themselves with their political bloc when announcing the day, although any political motivations are "alleged" and not acknowledged.
There's no central authority in Islam like the clergy in Catholism.
However there are legal schools and councils that people trust. Legal schools (or fiqh) were established by famous scholars that nearly everyone recognizes as an expert and were carried on by their students.
From a political standpoint, a lot of Muslims defer to Saudi Arabia because they are the current caretakers of Mecca and Medina.
But generally speaking for everyday normal Muslims they go with whatever their local imam says and go with whatever method the imam used because they are usually the most knowledgeable person around on such matters.
The choice of which community or authority to follow is also a personal preference. People often express their preferences in a way that aligns them tribally in one sphere or another when given the choice, and the lunar calendar is (humorously) not an exception to that.
There are no central authorities, only a menu of organizations and traditions that one can choose from. In some cases there is social pressure to choose one, and that social pressure is sometimes intense enough so that it feels like there is a central authority.
According to Islamic rulings if there’s a global caliphate every muslim in the world is required to obey that (there’s not one since 1915s). But besides that, all of the religion of Islam (rulings, practices) is capable of graceful degradation, scaling down to even just one person. If there was literally one muslim left on the face of the earth, that muslim would not lack anything in his practice of religion, virtousness or his connection with God. There’s no middleman to God like Christian (Catholic?) priests. Similarly if a group of muslims were to crash on an island in a plane accident, they’ll (and are required to) establish islamic order (sharia) there and function all by themselves. Islam is completely decentralized in this way.
