How should the beginning of an Islamic Month be determined?
In modern astronomy, the term ‘new moon’ refers to the phase when the earth, moon, and sun are aligned; this is also known as the lunar conjunction. The alignment of the earth, sun, and moon leaves the side of the moon that faces earth in complete darkness. During this phase of conjunction, it is impossible for the moon to be sighted in the sky.
The following image illustrates the phase of the new moon conjunction:
As the moon is in constant orbit, moments after the lunar conjunction, the dark side of the moon is exposed to sunlight. Although during this period, the moon cannot be seen with the human eye, it is possible to sight it using advanced technological aid. Traditionally, the beginning of an Islamic month is determined when the new moon is sighted. However, Muslim scholars have not always agreed on what is meant by the sighting of the new moon and how it is ascertained. This has led to the following questions:
ICCI MAJORITY OPINION
The beginning of a new Islamic month is determined immediately after the lunar conjunction, as soon as the part of the moon facing the earth is exposed to direct sunlight and is out of the dark moon phase. In other words, it is determined as soon as the first photons of light originating from the sun are reflected from the moon to the earth. The visibility of the new moon does not have to be physically sighted (either with a naked eye or any other technological aid) from the earth, rather astronomical calculations that determine the precise time and date of the moon coming out of conjunction are sufficient to determine the beginning of a new Islamic month.
1. It is generally believed from the verses of the Quran that the Islamic calendar is based on the lunar cycle of the moon. The verses of the Quran describe the great benefits of this natural occurrence. However, they do not prescribe a detailed method of how to determine the beginning of a new Islamic month. The verse 2:185 pertaining to the commencement of the Islamic month of Ramadan states: “Whomsoever among you witnesses the month [of Ramadan], then let them fast”.
2. Narrations explicitly mention ruʿya (sighting of the new moon) as a method to determine the beginning of a new Islamic month. However, most of these narrations were given in the context of refuting the following two pre-existing positions with regards to moon sighting:
These narrations indicate that ‘sighting’ (as opposed to completing 30 days or predicting) is a more accurate and reliable ‘means’ (ṭarīq) of establishing the start of a new Islamic month. Therefore, it is found that the narrations do not provide details of sighting, such as whether the new moon should be sighted in an individual’s place of residency or anywhere in the world; or whether the sighting should occur with the use of the naked eye; or if technological aids or astronomical calculations are sufficient.
A thorough analysis of the hadith literature therefore leads to the conclusion that a ‘sighting’ of the new moon was the most reliable and accurate means available at the time to determine the beginning of a new Islamic month. Accordingly, it can be concluded that the primary criteria set forth in the hadith literature is of reliability and accuracy. During the presence of the Prophet and Imams, the most convincing method of determining the natural occurrence –or what the Quran describes as a beneficial cosmic event – of the birth of the new moon, was ruʿya (sighting).
3. Present day astronomers can scientifically calculate the different phases of the moon. They have access to resources that allow them to accurately pinpoint the different phases of the moon. Thus, modern astronomers can tell us in advance the time and dates of the new moon conjunction, and when it will come out of the conjunction. Based on the understanding that sighting (ruʿya) of the new moon has no value apart from it being an accurate means of establishing that the new moon is out of conjunction, it can be proposed that in the present day the most accurate way of establishing that the new moon is out of conjunction is to rely on astronomical calculations. If in the future a more reliable method of establishing the new moon is found, then that should be given preference over the current method of astronomical calculations.
4. Since the emergence of the new moon is a natural cosmic occurrence that can be astronomically calculated, it must be applicable to all regions that share the night.
Please note that ‘night’ occurs from sunset to dawn (i.e. the time of fajr prayers). If the moon comes out of conjunction at any moment during the night, that day marks the first of the Islamic lunar calendar. On the other hand, if the moon comes out of conjunction during the daytime, the following day will mark as the first day of Islamic calendar.
ICCI MINORITY OPINION
The beginning of an Islamic month is determined when the new moon can be sighted from any location of the earth that shares the same night. The sighting of the new moon does not necessarily have to be physical (i.e. either with a naked eye or any other technological aid), rather a person can choose to follow astronomical calculations that determine the sighting, providing they give him/her sufficient assurance (iṭmiʾnān).
1. The Quran does not define a clear method on how to determine the beginning of a new Islamic month. The verse 2:185 pertaining to the commencement of the Islamic month of Ramadan states: “Whomsoever among you witnesses the month [of Ramadan], then let them fast”.
2. The narration from Imam Jaʿfar al-Ṣādiq explicitly mentions: “Fast when you see the moon.” This hadith demonstrates that the sighting of the new moon from the earth is an essential criterion to determine the start of the new Islamic month.
3. The physical sighting of the new moon with the naked eye or a technological aid is not always possible from different parts of the world. Accordingly, if an individual attains sufficient assurance (iṭmiʾnān) from astronomical calculations that suggest that the new moon can be sighted from earth, then he/she can follow the results of this calculation.
4. Sighting can be done from anywhere around the world that shares a night or a part of a night. The basis for this justification can be found by scholars who uphold the notion of the ‘unity of horizon’. In accordance with this notion, the moon does not have to be sighted within the horizon (or in locations that have the same probability of crescent visibility) of an individual’s residence. Rather it can be sighted anywhere around the world, so long as the place where the moon is sighted shares a night, or a part of a night, with a country in whose horizon the moon cannot be sighted.
 Quran 2:189, 10:5, 36:39, 55:5.
 For a detailed study of the narrations, see Shaykh Tūsī, Tahdhīb al-aḥkām, 4:154-180
 Wasāʾil al-Shīʿa, 7:210.
 For a detailed discussion on the opinions of scholars who uphold the notion of ‘unity of horizon’ see Ayatollah Khūʾī, Kitāb al-ṣawm, 2:115-124.
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