Disagreements regarding determining when the new monthstarts have become commonplace amongst Muslim communities, especially when it comes to establishing the first of Ramadhan and Shawaal. This is because the Islamic calendar is a lunar calendar where each month commences on the birth of the new lunar cycle and lasts for 29 or 30 days depending on the visibility of the moon. Traditionally, this is based on actual observation of the moon's crescent (hilāl) marking the end of the previous lunar cycle and hencethe previous month, thereby beginning the new month. However, Muslim scholars are not in agreement on how exactly the new month is determined and whether physically sighting the moon is a requirement. The Qurʾan mentions the new moon (ahilla)as a means for tracking time in the the verse,
“They ask you, [O Muhammad], about the new moons. Say, "They are measurements of time for the people and for Hajj."1
Similarly, the verse regarding the commencement of the month of Ramadan states,
“whomsoever among you witnesses it (the month), then let them fast.”2
According to these verses, the ‘new moon’ is the subject for the beginning of the new month. The verses do not specifically mention sighting the moon per se. What is important here is that in essence the new month is determined by the new lunar moon, no matter how it is ascertained. However, according to the Arabian context of the time, the only way to determine the new lunar month was through actually sighting the new crescent. At the time there were no optical aids, such as telescopes and therefore, the crescent had to be visible to the naked eye to establish the commencement of the new month. Also, there were no calculations that could determine the birth of the new moon and the possibility of its visibility. And whilst sighting (ruʾya) is mentioned in hadith literature,3 it is possible to say that this was referring to a means (tariq) of determining the new moon, especially because there were no other means possible at the time.
It is possible to distinguish between sighting and sightablility of the new moon. Physical sighting can be with the naked human eye under normal conditions or by virtue of any other instrument. The sightability on the other hand is determined by astronomical calculations on the possibility of seeing the crescent under varying circumstances. Potential sightability of the crescent is immediately after the point of conjunction and is therefore a point of reconciliation between the new moon and ruʾya to mean sightability in the broadest sense. Accordingly, the new month may be determined through the potential sightability of the new moon since there are accurate scientific calculations which give us this knowledge in the present day.
The determination of the new moon through the Qur’an and Hadith hinges on two notions: ahilla (new moon) and ruʾya (sighting or sightability of the first crescent). Ahilla does not specify how the new lunar month commences since it is a designation for the new month in whatever way it is determined. However, the ahilla assumes discernible new moon in the Arabian context of the time. Ruʾya on the other hand denotes visibility of the first crescent to the eye however it is open to interpretation as to whether the visibility is actual or potential.
1. 2:189
2. 2:233
3 Sahih Muslim, Kitab al-Sawm, Book 6, Number 2363: Ibn Umar (Allah be pleased with both of them) reported Allah's Messenger (may peace be upon him) as saying in connection with Ramadan: Do not fast till you see the new moon, and do not break fast till you see it; but if the weather is cloudy calculate about it.
Shaykh Tūsī, Tahdhīb al-aḥkām, 4:154-180; Wasāʾil al-Shīʿa, 7:210.