The Grand Ayatollah Sistani, Shia Supreme Religious authority, has provided an important answer to a question about sighting of the new moon crescent with instrument.

Answer:
This is a specialized discussion, some aspects of which cannot be clarified except for experts, but as far as it is understandable to others, we indicate some points and say that: The Holy Quran implies that “the moon crescent of each month” is set as “the time index” for the general public to rely on in their religious and worldly work. The God Almighty has said: “They ask you, [O Muhammad], about the new moons. Say: They are measurements of time for the people and for Hajj”, and what is worthy to be fixed time or place and the index of time for the general public is the moon crescent which is visible to the naked eye in the local horizon of any region; But if this crescent is seen only with a camera, it does not have the validity to be considered as an indicator of time for the general public.
In other words, every month, the crescent of the first night and its position in the following nights is considered as the pointers of the clock, and just as the pointers show different times of day and night with their circular rotation, the different forms of the moon which in consecutive nights, its bright part becomes more and more, and then this bright part decreases from the middle of the month until it reaches the end, is the same and it is considered as a celestial night- counter for the lunar month, and therefore it must be seen in a way that is accessible to the general public and does not require special tools.
Thus, it is clear that distrust in observing with a telescope and similar tools in proving the first day of the month is not due to the disregarding of modern tools in determining the subject of the Sharia decree, but because what is the subject of the Sharia decree is something that its existence must be recognizable to the general public, and anyone with a healthy eye, even villagers and nomads, and mountain dwellers who have no tools other than their eyes to detect a crescent on the horizon, can use it.
In a way, this can be compared to the issue of one of the causes of Janabah, which is the discharge of semen from a man; in the way that in case of surgery and removal of the prostate gland, during intercourse, semen returns to the bladder and comes out of it with the urine, and if the person’s urine is tested, it is determined by laboratory tools that the urine contains some live sperms, but despite this, he will not be required to perform Ghusl; because the reason for the necessity of Ghusl is the discharge of semen, and this is something that has not been realized, and the presence of sperm in the urine that has been given to the laboratory, has no effect on the decree; because the reason for the necessity of Ghusl has not been realized.
Another similar case is when a person leaves his city and become so far away that the residents of the city cannot see him except with a camera and similar tools, and he cannot hear the call to prayer (Adhan) of his city except with instruments that can increase the loudness of the distant sound. However, the Sharia decree on the issue of Had-at-Tarakhus has nothing to do with these tools and equipment, but that person reaches the Had-at-Tarakhus when his fellow citizens can not see him with their normal eyes, and when he cannot hear the call to prayer with his normal ears. Because the subject of the decree on the Qasr prayer and Iftar permission during the holy month of Ramadan is just to become far away from the city as much as above mentioned, not the case of not seeing him and not hearing the call to prayer.
Another similar thing is that if one cleans the fish from the blood in it, and of course it is forbidden to eat it while is pure, then by a magnifier he see very small particles of blood in it that cannot be seen with the naked eye, so according to the Sharia, it is not forbidden to eat that fish because the subject of the decree is on the sanctity of something which in practice is considered as blood; and this is not the case with particles that cannot be seen with the naked eye. Therefore, the above mentioned cases are different from other cases in which new tools may be relied upon in the realization of the subject of the Sharia decree or its fulfillment; examples of the effectiveness of these devices include:
When one doubts about meet the water of a container with impurity and does not find impurity in the water with the naked eye, but when he finds a particle of impurity with practical tools; in this case, the verdict is that the water is unclean; because the subject of the rule of the water impurity is finding even a little bit of impurity, and now he has been able to achieve the smallest detail by a magnifier.
When one looks at something, such as the body of a non-Mahram woman, from a distance with a camera or similar devices; will be guilty; because the subject of sanctity is the gaze, and this gaze is now realized with the instrument.
When a person investigates with the modern means of eavesdropping, then he has committed a forbidden act; because the subject of the sanctity is not listening without tools, but the title of “spying.”
When a pregnant woman’s husband dies and they want to share the deceased’s inheritance among the other heirs after reserving the fetus’ share, if they use a device such as an ultrasound to determine the condition of the fetus, whether they are twins or not or what is the sex of the baby, the result will be considered because this is the subject of the decree, that is, the obligation to exclude the share of carrying from the deceased’s inheritance before division, is based on the fact that the fetus is one or two and whether it is a boy or a girl, and if it can be identified with modern tools, it must be acted upon.
When identifying the father of a baby is found to be in doubt and he or she is tested for DNA genetics and his or her gene is coordinated with one of the individuals, the sentence will be based on it. Because the subject of the decree of filiation of an individual requires that one of man’s consanguinity have given birth to the child, which can be identified with this experiment, and therefore, the decree of filiation will be applied to him/her. Requires that one of man’s consanguinity must have given birth to the child.
As a result, the distinction between the cases in which new visual and or auditory devices and the like can be applied to some of them, and the cases in which these tools should not be considered, depends on the difference in the subject of the Sharia decree, and the jurist has no choice but to adhere to what uses as reasons.
In the case of the moon crescent, most jurists have explained the term “measurements of time for the people” for the crescent in the holy verse, as the crescent is a general tool for measuring time that all people can refer to and organize their livelihood and religion according to it, not as an indicator that only some people can afford to use, and others can’t use it except by referring to those who have the tools to see the crescent.
Thus, it turns out that even if scientists had succeeded in inventing the telescope during the time of the Infallibles, they would not have considered the observing of the moon crescent to be valid; This, of course, does not mean ignoring the help of modern tools and equipment, but it does mean that the crescent has not been designated as an indicator of their time until it appears to the public.
With this in mind, it becomes clear that the aforementioned “observing” in the narrative texts related to fasting and iftar is only a way for the crescent to appear on the horizon of any region, so that it can be seen by the general public and with the naked eye, and no meaning for observing with the camera is understood from it.
Furthermore, if we assume that basis for the beginning of the new month be the appearance of moon crescent on the horizon in such a way that it can be observed, even with the most equipped telescopes and cameras, then it should be mentioned that many fasting, iftar, Hajj, and other acts done by the Prophet (PBUH) and the Imams (A.S), which must be performed on certain days of the month, were not in their true days(times); because those Infallibles(Peace be upon them) in recognizing the first day of the lunar months, had trusted in observing with the naked eye, while they, like many other people of their time, knew that the moon of the first night of the month is hardly visible with the naked eye and could be seen clearly and at high altitude, unless it can be seen the night before with a powerful tool – if any.
How is it that neither he nor the others have been told that when the moon is high and clear for the first time, it should be considered as the second night of the month?!