Bismillah. This is what happened:
Saudi claimed to have seen the moon on Thursday 19/7 and began Ramadan on Friday 20/7; many other countries followed suit. However, we know definitely that such a sighting was impossible, for at least two reasons:
(i) from precise astronomical calculations (www.crescentmoonwatch.org )
(ii) had it been genuine, there would have been an easier sighting from the Southern US and Central America on the same date, which there wasn’t. Refer to Ibn Taymiyyah’s fatwa on moonsighting (elsewhere on this blog), as well as Sheikh Afif al-Akiti’s detailed treatise on the subject.
However, the ECFR (www.e-cfr.org ) had already announced that Ramadan would begin on Friday 20/7, due to the expected visibility of the crescent moon from South America on 19/7. The ECFR mentioned Santiago (Chile) in its declaration. Note that the ECFR’s declaration implied that they agreed that moonsighting was impossible in Saudi on that date, but ruled that the Chile sighting was enough for the whole world, even if it occurred many hours after local sunset elsewhere: e.g. the ECFR method required Australia to begin Ramadan on 20/7, even though they are about 12 hours ahead of Chile.
Note also that this ECFR method is consistent, and is a possible approach to determining Arabian/Islamic lunar dates worldwide, using the solar date-line as an effective lunar date-line. If people agree to use this method, it is a possible solution to the moonsighting problem, although we will need to check that it gives a reasonable pattern of 29/30-day months.
Amongst Sunni Muslims, there were three start dates:
(i) Friday 20/7 – those following the impossible Saudi sighting or the plausible ECFR method
(ii) Saturday 21/7 – those following the easier sightings around most of the world on the next day
(iii) Sunday 22/7 – for northern latitudes such as the UK, those following a local sighting.
Amongst Shia Muslims, the same three start dates were observed, based on people following the fatwa of their authority (marja’), whether Fadlallah, Khoei or Sistani respectively.