The beginning of the month is established by physically seeing the crescent, or by the testimony of two trustworthy witnesses, among other ways. If one was certain that he saw the crescent, then he must consider it the first of the month, in both mentioned cases.

If the crescent was seen in one of the countries of Europe, Asia, Africa or Australia, then the beginning of the month is confirmed in all the countries of the world. However, if it was seen in the continents in North or South America, the month is not confirmed in other continents.

If the new moon has been ascertained through the religiously valid way in any place in the Americas, then one should act upon it in all the regions of the Americas. If the sighting of the new moon has not been established, but there is certainty derived from scientific calculations that the new moon has reached the level where it is possible to be seen by the naked eye, then one should act upon that too. If there is no such certainty, then one should assume that the month is continuing until the completion of thirty days.

What has happened in recent years is because of the differences in the ijtihad and in interpretations of the sources and narrations from the Imams of the Ahlulbait (peace be upon them). Some religious authorities – including his Eminence Sayyid Al-Hakeem (may Allah prolong his life) – have the opinion that the narrations from the Ahlulbait (peace be upon them) prove that most countries can have one Eid in such a way that if the crescent was seen in a country, it is sufficient to establish Eid in other countries as well, even if the distance between the two countries is relatively far. The details of the verdict of his Eminence are explained in his books of Islamic Laws. However, some other Maraji have the opinion that seeing the crescent in a country will prove it to be the night of Eid for other countries only if they share a horizon, so such sighting does not necessarily prove the Eid in other distant countries.
If the differences in the edicts originate from the differences in Ijtihad and understanding of religious texts, then it is unavoidable, since a Mujtahid cannot change his opinions that are based on his own Ijtihad and research simply because of social pressure or similar reasons that are not related to what the religious texts indicate as per his understanding. As a matter of fact, doing so is considered as compromising against his duties in finding religious realities. Differences of these types indicate the authenticity of the Shia sect, and the piety and sincerity of its followers.
The Marja’ tries his best – via his research and teaching – to reach the religious realities. At the same time, the believers try their best to find out the most knowledgeable Mujtahid who fulfills all the criteria of the Marja’ and to act upon his edicts. This shows the strength of faith that these two groups possess.
Difference in opinions should not lead to conflicts or aversion. It should rather be dealt with calmness and wisdom for the sake of unity and the general interests of the believers.

The New Moon cannot be seen usually before sunset, since the light of the sun prevents its sighting, and if it is seen after sunset it proves that the next day is the first day of the month.

Australia and those counties fall in the same horizon, so it is permitted for these countries to follow the New Moon sighting reports in other countries with the same horizon, as long as the reports are valid as per the detailed laws.