We will briefly look at the criterion or criteria involved in the determining of the new moon.
Based upon the understanding that night precedes the day and that east precedes the west if the moon were to be established in any region of the of the world then the moon in relation to the regions which are west of it will be established without any major disagreement among the scholars. The areas of problem are the eastern regions to the place where the moon has been established. This is due to the reasoning that since the east is before the west and that night is before the day, the eastern regions prior to the establishment of the first moon have already embarked upon a new day and thus the moon will be considered to make the first of the month the next day.
The major issue is however regarding the criterion used to establish the new moon. Whereas according to some it is the possibility of or the physical sighting of the moon others contend that it is merely the birth of the new moon and yet others are of the opinion that both the factors equal. That is to say the moon's birth and its sighting.
As for the first group they maintain that it was the practice of the blessed Prophet and it is in accordance with his instructions that the moon be sighted by the naked eye. At most what can be said is, that by whatever method, if it can be ascertained that the moon might be seen by the naked eye but is unseen due to an impediment, then that would be sufficient to determine the first day for that region and regions west of it.
As for the second group they assert that the physical sighting of the moon was a mere means for ascertaining the birth of the new moon and hence the real criterion for determining the new moon is its birth. Therefore there would be no need for the sighting of the moon if its birth can ascertained by other means since sighting itself is a mere means of ascertaining its birth. There is a difference among the advocates of this reasoning insofar as the time of the birth of the moon. Whereas some maintain the birth has to be prior to the setting of the Sun in order to declare the next day as the first by its birth others see no difference as regards the time of its birth, prior to or after the sunset.
A case much similar to the first group who support the physical sight