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Most jurists do not consider sighting the crescent with an optical aid as valid [for establishing the first day of a subsequent month] for either the viewer or others. Even then, some people ask about the essence of this ruling given that the sighting mentioned in narrations (i.e., fast after sighting [the crescent of the month of Ramadan] or end your fast after sighting [the crescent of Shawwal]) potentially could include both sighting with the naked eye and with an optical aid. Thus, usage of an optical aid [for this purpose] should not be prohibited despite its unavailability during the time of the infallibles (pbut). Given this, what is the reason for not relying on modern devices to sight the crescent, especially since they are used to clarify, establish, or confirm various other religious issues?
The evidence and justification for these edicts comes from specialized research, which is not accessible in some aspects except to experts [in the science of jurisprudence]. However, what follows is a partial and non-technical explanation that should be comprehensible to the layperson.
The Holy Qur’an indicates that [sighting of] the crescent moon [at the start] of the months has been established as a reference point that people rely on in their religious and worldly affairs, Almighty God says, “[(Muhammad), they ask you about the different phases of the moon. Tell them that they are there to indicate to people the phases of time and the pilgrimage season.]” (Qur’an 2:189). The appropriate reference point for designating the appearance of the crescent on the local horizon for the public is viewing by the naked eye. As such, it is not acceptable (i.e., suitable) for the public that this reference point is a sighting that can only occur with an optical aid.
In other words, the crescent on the first night of the month and subsequent nights is just like the clock. The moon in its various states progresses in brightness, increasing one night after another, and then begins to decrease until it reaches the new moon phase (mahaq). This progression indicates the number of nights in each lunar month just as the hands of the clock [physically] show the movement of time through day and night. Thus, the phrase “different phases of the moon. . .indicate to people the phases of time” signifies that the various stages and progression of the moon during the month, which the public can witness, is an indicator they can reference to know the [exact] lunar day to organize their religious and worldly affairs. This entails that the crescent should be easily [and confidently] sighted by the public and not only by those who possess an optical device (i.e., allowing the latter to see the crescent on the horizon when it is not possible for the public to do so with the naked eye). It would not constitute application of the different phases of the moon as an indicator of time to all people if optical aids were allowed.
Hence, the lack of reliance on telescopes and similar devices to verify the crescent moon is not due to reluctance to use modern devices to establish the subject (i.e., criteria) of the religious ruling. Instead, it is due to the fact that the criteria for establishing the crescent according to religious law is sighting by the public (i.e., those with visual acuity), such as people in the countryside and those living in remote places like prairies and mountains who have no way of sighting the crescent on the horizon except with the naked eye.
Similarly, consider the example of the ejaculation of semen from a man's private part which causes him to be in the state of janabah. If the prostate gland is removed, the semen will no longer be ejaculated but rather absorbed into the bladder and dissolved in the urine. In such a case, if a sample of that urine is taken to a laboratory and examined under a microscope, some sperm cells may appear in the urine. Yet, the person would not have to perform a ritual bath (ghusl) because the criterion for doing so is ejaculation of semen, which did not occur. As such, establishing the presence of sperm in the urine via the modern device (e.g., microscope) would not obligate the need for a ritual wash given the criteria of janabah, which did not occur.
Also, take the case of a person who travels outside their hometown (watan) and reaches a distance where the residents of the town cannot see them except through a telescope, or the traveler can no longer hear the sound of the call to prayer (adhan) except with a device that can capture sounds from far away. The increased ability to see or hear [due to the devices] does not prolong the time it takes for the traveler to reach the religiously prescribed limit (i.e., hadd al-tarrakhuss or where the traveler shortens their prayer or breaks their fast) because the criteria is that the residents of the hometown cannot see the traveler with the naked eye. On the same basis, other religious criteria are based on the traveler being unable to hear the call to prayer (adhan) with their normal hearing. Thus, the criteria for shortening the prayer and breaking the fast during the month of Ramadan is traveling outside the hometown and passing the required distance [that would fit this condition] and not the inability to see the residents of the town or hear the call to prayer (adhan) per se.
Likewise, there is no problem in eating a fish if a person cleans out the blood, which is unlawful to eat despite being ritually pure, but sees remnants of very small particles of blood under a microscope (i.e., they are not visible with the naked eye) because the criteria for prohibition is the presence of blood that is commonly seen and noted by people (urf), whereas the very small particles [that are only viewable by microscope] are not considered that.
These cases differ from other cases that might have a role for modern devices in establishing the subject or conditions of the ruling. For example:
• A person doubts whether an impurity has fallen in a glass of water and cannot see it with the naked eye. However, they see a very small amount there after using a microscope. In such a case, the water is considered impure (mutanajjis), even though the pure water came into contact with a microscopic particle of impurity, because the condition for the ruling of impurity is a pure subject comes into contact with an impurity, irrespective of its quantity.
• If a person looks at something that is unlawful to look at, such as the body of a non-mahram person of the opposite sex using binoculars or another optical aid, the onlooker has committed a sin because the condition of unlawful act is looking, which has occurred, albeit with an optical aid.
• If a person spies on others with a modern eavesdropping device, then they have committed something forbidden because this act meets the conditions of spying, which is to spy or eavesdrop on others in any way, and not just without a device.
• If a pregnant woman’s husband dies, it is vital to know the number of fetuses [she is carrying] and their genders to divide the inheritance. If an ultrasound can be used to identify the number and gender of the fetuses, then because the conditions of the ruling of allocating the inheritance of the fetuses is to know their quantity and gender, albeit with modern devices, then it must be to act according to its results.
• If a person suspects that a child is their biological offspring and a DNA test confirms that their genes match, then they must act according to the results. This is the case because the condition of establishing heredity is confirming that the child was formed by the father's sperm, which can be verified by the DNA testing. Therefore, they must act according to its results.
In conclusion, relying on modern devices for observing or hearing in some cases and not doing so in others depends on the type of legal resources available to the jurist. This is determined by religious evidence. As such, the jurist is restricted to these limits and must arrive at his conclusion from that evidence.
In the case of the crescent, most jurists conclude that it is an indicator of time for people as stated in the holy verse mentioned above. It is a timescale that the public can employ to organize their daily and religious affairs. Moreover, its usage is not limited to certain people such that the rest cannot benefit from it unless they refer to those who have access to an optical aid. Therefore, even if scientists had been able to invent optical aids during the time of the infallibles (pbut), the latter would not have relied on them in sighting the crescent. This would not have been out of reluctance to use technologically advanced devices, but because the crescent that is not visible to the public (i.e., by the naked eye) is not [religiously] considered an indicator of time for them. With this presumption, sighting, which is mentioned in religious texts for starting and ending the fast [of the month of Ramadan], is a means to establish the appearance of the crescent on the local horizon such that it is visible to the naked eye for the public, and there is no absolute signification (itlaq) in the religious texts to include sighting with an optical aid.
In addition, if establishing the beginning of the month is based on the appearance (i.e., visibility) of the crescent on the horizon, albeit through the use of the most powerful telescopes and optical aids, then it would suggest that the fasting of the Prophet (pbuh&hp) and the Imams (pbut), as well as the breaking of their fasts, their pilgrimages (hajj), and other special rituals that are established at specific [lunar] times, would not have occurred at the appropriate times. Therefore, the infallibles (pbut) depended on ordinary vision (i.e., with the naked eye) to clearly establish the beginning of the lunar months.
The infallibles (pbut) and many of the informed individuals who lived during their time were aware that the crescent is rarely sighted with the naked eye, clear and high at night, [and even if sighted] it may have been possible to sight it in the previous night with a strong optical aid if it was available. So, why did they not count the crescent when it was sighted high and clear for the first time with the naked eye as night two (i.e., having realized it was observable one night before with the optical aid)?
All praise is due to Allah the Lord of the worlds.
Office of al-Sayyid al-Sistani (may Allah prolong his life), The Holy City of Najaf