Makes more sense now.
Eid Mubarak!
The charitable case is that while something might be predictable, it's our conscious interaction that's important to these religions, not the theoretical knowledge.
The uncharitable case is that religions derive a lot of power from being able to fix time, and this demonstrates their sovereignty over people's lives in this sphere.
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 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.
At the end of the day you just follow whatever mosque you go to. If you want to follow moonsighting but your mosque does calculation, where do you go to celebrate Eid if the days differ?
Personally I wouldn't go to a mosque that uses moonsighting because I like predictability. My boss is Muslim so she would understand but it's still annoying for the company if I just went "I'm off tomorrow byeee" the night before.
I imagine some Muslim countries differ in the same way (some use calc some use sighting), though I can't say off the top of my head which countries use calculation.
- Follow Saudi Arabia (Mecca)
- Use astronomic calculations
- Moon needs to be sighted with naked eye in the local city
- Moon needs to be sighted with any tool (telescope) in the local city
- Moon needs to be sighted with naked eye anywhere in the world
- Moon needs to be sighted with any tool (telescope) anywhere in the world - ...
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.