Praise be to Allah the Lord of the Worlds.
Moon sighting differences refer to difference in the birth time of the new moon and its sighting in different countries. This leads to difference in the start of the lunar calendar and consequently the start of Ramadan, and scholars have disagreed about the ruling of Sharia on that.
Shafie scholars stated that each country has its own sighting of the new moon, and so the start of the lunar calendar differs from one country to another. Countries that are far from each other, such as Hejaz, Iraq and Khorasan, have different moon sightings.
Whereas, countries that are close to each other have the same moon sighting. An-Nawawi (May Allah have mercy on him) said, "If the moon of Ramadan was sighted in one country, but wasn`t sighted in another while both countries are close, then both should start Ramadan on the same day.
However, if they were far from one another, then there are two opinions. The more correct one is that the people of the country in which the moon wasn`t sighted aren`t obliged to start Ramadan on the same day as the country in which it was sighted."{Rawdat At-Talibeen, 2/384}. According to Hanafi and one opinion of the Maliki and Hanbali scholars, difference in moon sightings is inconsiderable. If one country confirmed sighting the moon, then it is binding to all other countries: {They should start Ramadan on the same day}. Ibn Abdeen (May Allah have mercy on him) said, "Difference in sightings is inconsiderable, so the sighting of the people of the West is binding to the people of the East. If Egypt confirmed sighting the crescent, then this is binding to the people of all other countries."{Rad al-Mohtaar, 2/619}. As-Sawi (May Allah have mercy on him) said, "Difference in sightings isn`t considerable in our Madhab(School of thought). If it was sighted in one country then it is binding to other countries."{Hashyiat Al-Sawi, 1/225}. The Hanbali scholar Ibn Qhoddamah (May Allah have mercy on him) said, "If the new moon was sighted by the people of a country, then it is binding to other countries."{Al-Moghni, 3/107}.
In their stronger opinion, Maliki scholars have agreed with the Hanafi and Hanbali scholars that close countries should have the same sighting and that each of the far countries, such as the East and West, should have its own sighting. Kindly refer to {Mawahib Al-Jaleel, 2/384} by Al-Hattab (May Allah have mercy on him).
In conclusion, this is a controversial issue, but there is no blame in following any of the two aforementioned opinions. Moreover, the scholars are agreed that the opinion of the ruler, or whoever represents him, settles the dispute, and this is part of the religious policy. And Allah the Almighty knows best