“…. Pre-determine Of The Month
As communications in the Muslim community became more complex, there was a need to have predetermined months for scheduling purposes. It would be very inconvenient for people in the same region to be using different calendars. Since the visibility of the crescent was not predictable in advance, another method would have to be used.
One such method was the new moon conjunction, which, in astronomical terms, is when the moon is precisely between the Earth and Sun. During conjunction [which is also known as moon-birth] the moon is not visible from Earth because the sunlit portion of the moon is facing away from the Earth.
New moon conjunction is precisely predictable and can be calculated exactly. The crescent moon only becomes visible from Earth about a day or two after the new moon conjunction because even when the three celestial bodies are not in a straight line, the moon is still too close to the sun’s glare to be seen with the naked eye from Earth. It is important to understand that the moon is ‘born’ about one or two days before it is actually visible, so moon-birth and moon-visibility are two entirely different things.
Another method which was adopted in 1420 AH/1999 by the Ummul Qura calendar in Saudi Arabia was that if moonset occurs after sunset in Makkah on the 29th day of any month, then the month is over. This calculation is also precisely deterministic and took into consideration a time that is closer to the visibility of the moon than conjunction.
The Fiqh Council of North America [FCNA] and the European Council for Fatwa and Research [ECFR] have adopted a similar approach where the presence of the moon above the horizon at sunset anywhere on the globe is the criteria. This is precisely determined when the elongation of the moon is at least eight degrees and it is at least five degrees above the horizon.
Which Callender Should Determine Ramadhaan?
As can be seen, even predetermined calendars which are calculated according to precise measurements require some specific methodology, such as conjunction, moonset-after-sunset, or some other precise measurements. The differing methodologies will result in different calculated calendars.
The question arose among Muslim scholars: should Ramadhaan, and other religious days of fasting/celebration such as the 10th of Muharram [‘Aashuraa’u] and the 10th of Dhul Ḥijjah [Eid al-Adhaa], be determined through actual crescent sightings or a predetermined calendar?
Several scholars argued that dates which have a religious significance should be determined through actual crescent sightings, the way the Prophet Muhammad did, and the calculated calendar can be used for civil purposes. Other scholars posited that a calculated calendar should be used for both civil and religious dates, the same way that it is used by most urban Muslims throughout the world for their prayer times, without having to actually check the light in the horizon for Fajr or the shadow-length for ʿAsr……………”
Extracted [Fiqh Ramadhan] page 47, 48 by Ibn Taofeeq Abdul Azeez.