Between the Eye and the Horizon

Understanding Hilal Visibility Criteria, Testimony, and Physical Impossibility — An Islamic Perspective

This article is written for Muslims who use or are interested in hilal (crescent moon) visibility tools, and who want to understand the Islamic legal and scientific foundations behind rejecting sighting claims that contradict established physical impossibility. It is not a fatwa. It is an invitation to think clearly about a matter that affects every Muslim household at least twice a year.

The Question Every Muslim Faces

Every Ramadan and every Eid, the same question arises across the Muslim world: Has the crescent been sighted?

For most of Islamic history, this was a straightforward matter. People would go out after sunset on the 29th day of the month, look toward the western horizon, and either see the thin arc of the new crescent — or not. If they saw it, the new month had begun. If they did not, they would complete thirty days and begin the month the following evening.

The Prophet Muhammad ﷺ said:

صُومُوا لِرُؤْيَتِهِ وَأَفْطِرُوا لِرُؤْيَتِهِ فَإِنْ غُبِّيَ عَلَيْكُمْ فَأَكْمِلُوا عِدَّةَ شَعْبَانَ ثَلاَثِينَ

“Fast upon sighting it [the crescent] and break your fast upon sighting it. If it is obscured from you, then complete the count of Sha’ban as thirty.” — Sahih al-Bukhari 1909, Sahih Muslim 1081

This hadith is the foundation. No Muslim disputes it. The month begins with ruʾyah — visual sighting.

But today, something new has entered the conversation: we now understand, through centuries of accumulated observation and modern astronomical science, that there are conditions under which no crescent exists to be seen. Not because of clouds. Not because of poor eyesight. But because the Moon is still so close to the Sun that no sunlight reaches its visible surface. The crescent has not yet formed.

This raises a profound question: If someone claims to have seen the crescent under conditions where it physically cannot exist, what does Islamic law say?

This question is where Muslims have genuinely disagreed — and where clarity is needed.

Two Positions, One Concern

Both sides of this disagreement share the same concern: faithfulness to the Sunnah of the Prophet ﷺ and respect for the testimony of Muslims. Where they differ is in how they understand the relationship between physical reality and legal testimony.

Position One: Testimony May Be Evaluated Against Physical Impossibility

This position holds that if the crescent is physically impossible to exist — not merely unlikely, but impossible, like seeing the sun at midnight — then a claim to have seen it is necessarily mistaken, regardless of the sincerity or uprightness of the witness. The witness may be truthful in believing they saw something, but what they saw was not the hilal. It may have been a bright star, a wisp of cloud illuminated by twilight, or an optical illusion near the horizon.

This position does not replace ruʾyah with calculation. It uses established empirical knowledge to evaluate whether a claimed ruʾyah could have actually occurred.

Scholarly support for giving calculation a role in crescent matters actually comes in two forms — and intellectual honesty requires us to distinguish them clearly.

First, a number of classical scholars held the broader position that astronomical calculation may serve as a positive basis for determining the month — a stronger claim than what this article argues. These include Ibn Surayj (d. 306/918), Taqī al-Dīn al-Subkī (d. 756/1355), al-Qarāfī (d. 684/1285), al-Zarkashī (d. 794/1392), and Muḥammad al-Ramlī (d. 1004/1596). What this article argues is actually weaker than what these scholars held. If they accepted calculation as strong enough to begin the month, they would certainly accept it as strong enough to say “that sighting was impossible.” Their broader position logically includes the narrower one.

Second, other scholars addressed our exact question more directly — using calculation not to start the month, but to reject testimony that contradicts physical reality. As we will see in detail below, Ibn Taymiyyah himself acknowledged that calculation may serve as a “private basis for accepting or rejecting testimony”. Among those who stated this principle explicitly:

• Al-Qalyūbī (Shihāb al-Dīn Aḥmad ibn Aḥmad, d. 1069/1659), the Shāfiʿī commentator. In his Ḥāshiyat al-Qalyūbī ʿalā Sharḥ al-Maḥallī ʿalā Minhāj al-Ṭālibīn, he stated: “All sighting-claims must be rejected if calculations show that a sighting was impossible. This is manifestly obvious. In such a case, a person may not fast. Opposing this is obstinacy and stubbornness.” (Also cited in al-Mawsūʿah al-Fiqhiyyah al-Kuwaytiyyah, vol. 22, pp. 36-38.)

Al-Qalyūbī’s statement is precisely the principle behind hilal visibility criteria: not replacing ruʾyah, but verifying that what was claimed to be seen could have existed in the first place.

Position Two: Testimony Cannot Be Overridden by Calculation

This position holds that the testimony of an upright Muslim (ʿadl) who claims to have seen the crescent should be accepted, and that astronomical calculations — no matter how precise — cannot serve as grounds to reject that testimony. Proponents of this view often cite the hadith commanding us to fast upon sighting, and argue that introducing calculation as a filter contradicts the simplicity and directness of the Prophetic command.

This position is rooted in a valid concern: that Islam should not become dependent on specialists and their instruments, and that the communal practice of moon sighting — accessible to every Muslim — should not be taken away.

Both positions have scholarly support. Both come from sincere concern for the Sunnah.

But we must ask: are they really talking about the same thing?

The Crucial Distinction: Speculation vs. Impossibility

The heart of the matter is this: there is a fundamental difference between speculative prediction and established physical impossibility.

Consider two scenarios:

Scenario A: A calculator says, “Based on my models, I predict the crescent will not be visible tonight because conditions are marginal.” The crescent has an elongation of 9°, it is above the horizon, and conditions are merely difficult. A skilled observer might see it; most would not.

Scenario B: The Moon is only 1° from the Sun. It set before the Sun did. Its age is 3 hours. Its elongation is below the Danjon limit. There is no sunlit crescent surface visible from Earth. The Moon’s illuminated fraction is 0.00002%. This is not a prediction — it is the physical absence of a crescent.

Scenario A involves probability and uncertainty. A calculator making claims about whether conditions are “good enough” is indeed engaging in speculation, and rejecting valid testimony on this basis would be wrong.

Scenario B involves physical impossibility. No crescent exists. This is not about atmospheric conditions, observer skill, or calculation models. It is about whether sunlight has reached the visible surface of the Moon at all. It is the same category of impossibility as claiming to see the sun at midnight, or claiming to see stars at noon with the naked eye.

The scholars who rejected the use of calculation were addressing Scenario A — and they were right to do so.

But Scenario B is a different category entirely.

What Ibn Taymiyyah Actually Said

No scholar is more frequently cited in this debate than Shaykh al-Islām Ibn Taymiyyah (d. 728/1328). His words from Majmūʿ al-Fatāwā (volume 25) are quoted by those who reject any role for astronomical knowledge in hilal matters. Let us read what he actually wrote — carefully and completely.

The Famous Passage

On page 132 of volume 25, Ibn Taymiyyah writes:

فَإِنَّا نَعْلَمُ بِالِاضْطِرَارِ مِنْ دِينِ الْإِسْلَامِ أَنَّ الْعَمَلَ فِي رُؤْيَةِ هِلَالِ الصَّوْمِ أَوْ الْحَجِّ أَوْ الْعِدَّةِ أَوْ الْإِيلَاءِ أَوْ غَيْرِ ذَلِكَ مِنْ الْأَحْكَامِ الْمُعَلَّقَةِ بِالْهِلَالِ بِخَبَرِ الْحَاسِبِ أَنَّهُ يُرَى أَوْ لَا يُرَى لَا يَجُوزُ. وَالنُّصُوصُ الْمُسْتَفِيضَةُ عَنْ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ بِذَلِكَ كَثِيرَةٌ. وَقَدّ أَجْمَعَ الْمُسْلِمُونَ عَلَيْهِ. وَلَا يُعْرَفُ فِيهِ خِلَافٌ قَدِيمٌ أَصْلًا وَلَا خِلَافٌ حَدِيثٌ؛ إلَّا أَنَّ بَعْضَ الْمُتَأَخِّرِينَ مِنْ الْمُتَفَقِّهَةِ الحادثين بَعْدَ الْمِائَةِ الثَّالِثَةِ زَعَمَ أَنَّهُ إذَا غُمَّ الْهِلَالُ جَازَ لِلْحَاسِبِ أَنْ يَعْمَلَ فِي حَقِّ نَفْسِهِ بِالْحِسَابِ … وَهَذَا الْقَوْلُ وَإِنْ كَانَ مُقَيَّدًا بِالْإِغْمَامِ وَمُخْتَصًّا بِالْحَاسِبِ فَهُوَ شَاذٌّ مَسْبُوقٌ بِالْإِجْمَاعِ عَلَى خِلَافِهِ.

“We know with absolute certainty, as part of the religion of Islam, that in matters dependent upon the crescent — such as the beginning of the fast, the time for Ḥajj, waiting periods, oaths of abstention, and the like — it is impermissible to act on the statement of a calculator who claims that the moon will, or will not, be seen. The widely-transmitted texts from the Prophet ﷺ regarding this are abundant. The Muslims have agreed upon this (ajmaʿa). No ancient disagreement is known in it at all, nor any later disagreement — except that some later jurists who emerged after the third century claimed that when the sky is overcast, the calculator may act upon his own calculation… This opinion, even though it is restricted to overcast conditions and specific to the calculator, is isolated and preceded by consensus against it (shādh masbūq bi’l-ijmāʿ ʿalā khilāfih).”

— Majmūʿ al-Fatāwā, 25/132-133

And earlier, he describes judges who rejected the testimony of upright witnesses because of what a calculator told them, calling such a calculator الْحَاسِبِ الْجَاهِلِ الْكَاذِبِ — “the ignorant, lying calculator.”

This is clear. Calculation cannot replace ruʾyah as the legal cause (sabab) for beginning the month. Ibn Taymiyyah considered this ijmāʿ — and even when he acknowledged the minority who permitted it under restricted conditions, he dismissed it as isolated. As noted earlier, we mention that minority (Ibn Surayj, al-Subkī, and others) for intellectual honesty. But even by their standard, what this article argues is far less controversial: we are not asking to start the month by calculation, only to verify that a claimed sighting was physically possible.

What Is Often Left Out

But Ibn Taymiyyah says much more in this same discussion — and what he says next is essential.

He Uses Astronomical Reasoning Himself

On page 104 of the same volume, Ibn Taymiyyah explains the fiqh of matāliʿ (horizons) using explicitly astronomical logic:

فَإِنَّهُ مَتَى رُئِيَ فِي الْمَشْرِقِ وَجَبَ أَنْ يُرَى فِي الْمَغْرِبِ وَلَا يَنْعَكِسُ؛ لِأَنَّهُ يَتَأَخَّرُ غُرُوبُ الشَّمْسِ بِالْمَغْرِبِ عَنْ وَقْتِ غُرُوبِهَا بِالْمَشْرِقِ فَإِذَا كَانَ قَدْ رُئِيَ ازْدَادَ بِالْمَغْرِبِ نُورًا وَبُعْدًا عَنْ الشَّمْسِ وَشُعَاعِهَا

“Whenever the crescent is sighted in the East, it must necessarily be visible in the West — and not the other way around — because sunset in the West occurs later. By that time, the crescent will have increased in brightness and moved farther from the Sun and its glare.”

He then describes this as:

فَهَذَا أَمْرٌ مَحْسُوسٌ فِي غُرُوبِ الشَّمْسِ وَالْهِلَالِ وَسَائِرِ الْكَوَاكِبِ

“This is an observable matter (amr maḥsūs) regarding the setting of the Sun, the crescent, and all the other celestial bodies.”

— Majmūʿ al-Fatāwā, 25/104

Look at what Ibn Taymiyyah is doing here. He is using astronomical facts — angular separation, increase in illumination over time, relative timing of sunset — to reason about crescent visibility. He calls this amr maḥsūs: an empirically observable reality, not speculative calculation.

He Distinguishes Between True and False Astronomical Claims

On page 132, immediately before the famous passage about the lying calculator, Ibn Taymiyyah makes a remarkable distinction:

ثُمَّ هَؤُلَاءِ الَّذِينَ يُخْبِرُونَ مِنْ الْحِسَابِ وَصُورَةِ الْأَفْلَاكِ وَحَرَكَاتِهَا أَمْرًا صَحِيحًا: قَدْ يُعَارِضُهُمْ بَعْضُ الْجُهَّالِ مِنْ الْأُمِّيِّينَ

“Those who communicate correct information based on computation, the configuration of the celestial spheres, and their motions — they are sometimes opposed by ignorant, unlettered people…”

He then says these ignorant opponents:

صَارَ يَرُدُّ كُلَّ مَا يَقُولُونَهُ مِنْ هَذَا الضَّرْبِ. وَلَا يُمَيِّزُ بَيْنَ الْحَقِّ الَّذِي دَلَّ عَلَيْهِ السَّمْعُ وَالْعَقْلُ وَالْبَاطِلِ الْمُخَالِفِ لِلسَّمْعِ وَالْعَقْلِ

“…reject everything the astronomers say in this field, without distinguishing between truths affirmed by revelation and reason, and falsehoods that contradict both.”

— Majmūʿ al-Fatāwā, 25/132

Ibn Taymiyyah is criticizing people on both sides. He criticizes the judge who rejects valid testimony because of a speculative calculator. And he equally criticizes the ignorant person who rejects all astronomical knowledge simply because some of it was misused.

He explicitly says that some astronomical facts are amr ṣaḥīḥ (correct matters), affirmed by both reason and revelation.

His Epistemology: Knowledge Comes from the Senses

In his work Al-Radd ʿalā al-Manṭiqiyyīn, Ibn Taymiyyah lays out his theory of knowledge, and it is deeply relevant here.

He writes:

وَلَا رَيْبَ أَنَّ الْحِسَّ يُدْرِكُ الْمُعَيَّنَاتِ أَوَّلًا ثُمَّ يَنْتَقِلُ مِنْهَا إلَى الْقَضَايَا الْعَامَّةِ

“There is no doubt that the senses first perceive particulars, and from them one moves to universal propositions.”

— Al-Radd ʿalā al-Manṭiqiyyīn, p. 363

He then explains how repeated empirical observation leads to universal knowledge:

فَالْحِسُّ بِهِ يُعْرَفُ الْأُمُورُ الْمُعَيَّنَةُ ثُمَّ إذَا تَكَرَّرَتْ مَرَّةً بَعْدَ مَرَّةٍ أَدْرَكَ الْعَقْلُ أَنَّ هَذَا بِسَبَبِ الْقَدْرِ الْمُشْتَرَكِ الْكُلِّيِّ فَقَضَى قَضَاءً كُلِّيًّا

“Through the senses one knows particular things; then when this is repeated again and again, the intellect grasps the shared universal factor and makes a universal judgment.”

— Al-Radd ʿalā al-Manṭiqiyyīn, p. 386

And — remarkably — he uses the Moon itself as his example of this process:

مِثْلَ أَنْ يَرَى اخْتِلَافَ أَنْوَارِ الْقَمَرِ عِنْدَ اخْتِلَافِ مُقَابَلَتِهِ لِلشَّمْسِ فَيَحْدِسُ أَنَّ ضَوْءَهُ مُسْتَفَادٌ مِنْهَا

“One observes the variation in the moon’s light depending on its position relative to the sun, and thus infers that its light is derived from it.”

— Al-Radd ʿalā al-Manṭiqiyyīn, p. 387

This is extraordinary. Ibn Taymiyyah himself derives an astronomical conclusion — that the Moon’s light comes from the Sun — through repeated empirical observation. And he considers this a valid, universal form of knowledge.

Putting It All Together

Ibn Taymiyyah’s actual position, when read in full, is this:

1. Calculation cannot replace ruʾyah as the legal basis for beginning or ending the month. As we saw above, he declared this ijmāʿ and dismissed the minority view as isolated.
2. The speculative predictions of calculators cannot override the testimony of upright witnesses.
3. But empirical astronomical truths — things known through repeated, sensory observation — are valid knowledge (amr maḥsūs, amr ṣaḥīḥ).
4. Rejecting all astronomical knowledge because some of it was misused is the error of the ignorant.

And there is a fifth point, often overlooked, that is perhaps the most directly relevant to our question. On page 133 of the same volume, Ibn Taymiyyah writes:

وَلَا رَيْبَ أَنَّ أَحَدًا لَا يُمْكِنُهُ مَعَ ظُهُورِ دِينِ الْإِسْلَامِ أَنْ يُظْهِرَ الِاسْتِنَادَ إلَى ذَلِكَ. إلَّا أَنَّهُ قَدْ يَكُونُ لَهُ عُمْدَةٌ فِي الْبَاطِنِ فِي قَبُولِ الشَّهَادَةِ وَرَدِّهَا

“There is no doubt that no one, while Islam is manifest, can publicly base his position on that [i.e., calculation]. However, it may serve as his private basis (ʿumdah fī al-bāṭin) for accepting or rejecting testimony.”

— Majmūʿ al-Fatāwā, 25/133

Read this carefully. Ibn Taymiyyah is making a distinction between two uses of calculation:

• Public legal reliance on calculation to start or end the month — this is what he categorically forbids.
• Private use of astronomical knowledge to evaluate whether a testimony should be accepted or rejected — this he acknowledges as something that occurs, and he does not condemn it with the same force. He uses the word ʿumdah (basis, support) — not a word of condemnation but of acknowledgment.

This is precisely the distinction that this entire article rests upon. The question was never whether calculation can replace sighting. The question is whether established astronomical knowledge can help a judge, a committee, or a community determine whether a claimed sighting is credible — and Ibn Taymiyyah himself recognized this as a distinct category.

The Fiqh Principle: Testimony That Contradicts Impossibility

The question of whether a judge can reject testimony that contradicts established impossibility is not new in Islamic jurisprudence. It has a well-established answer.

Imam Ibn al-Jawzī (d. 597/1201) writes in al-Mawḍūʿāt:

“Do you not see that if a group of trustworthy people all told us together that a camel entered the eye of a needle, the fact that they are all trustworthy is of no use to us or to what they are reporting, and it has no impact on their report, because they are reporting that something impossible happened. So with regard to any report that is contrary to reason or contradicts basic principles, you must realize that it is fabricated.”

— al-Mawḍūʿāt, 1/106

Imam al-ʿIrāqī (d. 806/1404) stated similarly:

“One of the things which prove that a hadith is fabricated is when it is contrary to reality.”

— Quoted by Ibn Ḥajar in al-Qawl al-Musaddad, p. 9

If the ulema apply this principle even to hadith reports — requiring that they not contradict established reality — how much more should it apply to the testimony of an individual claiming to see something that physically does not exist?

The testimony of a Muslim is sacred. It should not be rejected lightly, and rejecting it without basis is a serious matter. But testimony reports what the witness perceived. If what the witness perceived is impossible to have been the hilal, then the testimony is not false — the witness is simply mistaken about what they saw. Mistaken identification is not lying. A sincere, upright Muslim can genuinely believe they saw the crescent when what they actually saw was a bright planet, a thin cloud catching the last light of sunset, or an atmospheric refraction effect near the horizon.

Recognizing this protects the witness. It does not accuse them of dishonesty. It simply acknowledges human fallibility in observation — something every experienced hilal observer knows well.

The Disagreement of Matāliʿ (Horizons)

To understand why visibility criteria matter, we need to understand the classical fiqh disagreement about matāliʿ — horizons.

What Are Matāliʿ?

The Arabic word مَطَالِع (matāliʿ, singular: مَطْلَع, maṭlaʿ) refers to the point on the horizon where a celestial body rises. In fiqh, the “disagreement of matāliʿ” (ikhtilāf al-matāliʿ) is the question of whether a crescent sighting in one location obligates Muslims in a distant location to begin the month.

The Two Classical Positions

Ittiḥād al-matāliʿ (Unity of horizons): If the crescent is sighted anywhere in the Muslim world, all Muslims must act upon it. This is the position of most Ḥanafī, Mālikī, and Ḥanbalī jurists. As Imam Ibn ʿĀbidīn writes in Radd al-Muḥtār: the address in the hadith — “Fast upon its sighting” — is general, addressing all Muslims, not a specific locality.

Ikhtilāf al-matāliʿ (Difference of horizons): Each locality follows its own sighting. This is the primary position of the Shāfiʿī school. Imam al-Nawawī recorded that the correct opinion in the Shāfiʿī madhhab is that people are not obligated to follow the sighting of another locality.

Both positions are valid within Sunni scholarship. The four established schools of law all have evidences for their respective positions.

Why This Matters for Visibility Criteria

Here is where the discussion of matāliʿ connects directly to visibility criteria:

If someone claims to have sighted the crescent in Location A, and this sighting is used to obligate Muslims in Location B (following the principle of ittiḥād al-matāliʿ), then the question arises: was the sighting at Location A even physically possible?

Consider a real-world example: the Moon’s conjunction (new moon) occurs at 14:00 UTC on a given day. At sunset in Location A (which is at 17:00 UTC), the Moon is only 3 hours past conjunction, with an elongation of approximately 4°. This is below the Danjon limit — the physical threshold below which no crescent can form. No human, no telescope, no instrument of any kind can see a crescent that does not exist.

Yet if someone at Location A claims a sighting, and this claim is transmitted to Location B — which might be thousands of kilometers away in a different time zone — entire communities may begin their fast or celebrate Eid based on a physical impossibility.

The disagreement of matāliʿ was formulated by scholars who assumed, reasonably, that any claimed sighting was at least physically possible. They disagreed about how far a valid sighting should carry, not about whether impossible sightings should be accepted.

Visibility criteria provide the tool to verify this foundational assumption.

What the Science Actually Shows

The Danjon Limit: Where No Crescent Exists

In the early 20th century, the French astronomer André Danjon studied hundreds of crescent observations and discovered that below a certain angular separation between the Sun and the Moon, the visible crescent arc shrinks to zero. This minimum elongation is called the Danjon limit.

Different researchers have proposed slightly different values:

Below approximately 7° of elongation, there is no sunlit crescent surface visible from Earth. This is not a prediction. It is not a probability estimate. It is a physical fact, confirmed by over a century of observation by thousands of observers worldwide.

To put this in perspective: the world record for the youngest crescent ever seen with the naked eye is held by Stephen James O’Meara, who saw a crescent at 7.7° elongation in 1990. The world record for optical aid (giant 40×150 binoculars from a mountain in Iran) is held by Mohsen G. Mirsaeed at 7.5° elongation. Even with CCD imaging and infrared filters — technology that can detect things no human eye can see — the minimum elongation achieved is approximately 4° (by Thierry Legault and Martin Elsässer).

No human being in recorded history has ever seen a crescent below 7° elongation with the naked eye. Not once, in thousands of documented observations over many centuries.

This is exactly the kind of knowledge Ibn Taymiyyah described: repeated empirical observation leading to a universal judgment. It is amr maḥsūs — an observable reality.

The Visibility Criteria: Yallop, Odeh, and the Zones

Modern hilal visibility criteria, such as those developed by Yallop (1997) and Odeh (2006), are not arbitrary calculations. They are empirical models built from hundreds of actual sighting reports collected over decades.

Mohammad Shawkat Odeh, founder of the International Astronomical Center (ICOP) and the Islamic Crescents Observation Project, compiled 737 crescent observation reports from around the world. He analyzed each one — recording whether the crescent was seen with the naked eye, with optical aid, or not at all — and mapped them against physical parameters: the arc of vision (ARCV, the altitude difference between Moon and Sun at the optimal observation time) and the crescent width (W, measured in arcminutes).

From these 737 real-world observations, Odeh derived a mathematical function (the V-value) that produces a score for any given location and date. The score thresholds map to three zones of visibility:

Below Zone C, Odeh’s criterion returns “Not Visible” — meaning that out of 737 documented observation attempts, no one successfully saw the crescent under comparable conditions.

The app adds one additional distinction: when the criterion returns “Not Visible” but the Moon is above the horizon after sunset (meaning the conjunction has occurred and the crescent is geometrically “born”), the app marks this as Zone E — the crescent exists in principle, but no criterion predicts it can be seen by any means. When the conjunction has not yet occurred, or the Moon has already set, the area remains unmarked — there is simply no crescent at all.

Other criteria available in the app — Yallop (1997), Shaukat, SAAO, and Istanbul 1978 — include an additional Zone D (visible only with optical aid), because those models define finer gradations in the marginal territory. Some of these criteria also explicitly check the Danjon limit (approximately 7° elongation), below which no crescent light reaches the observer regardless of equipment.

The key insight is this: all of these criteria are built from empirical observation, not theoretical speculation. They represent what thousands of real observers — Muslim and non-Muslim, amateur and professional — have actually seen and failed to see over decades of documented attempts.

What the App Shows You

When you open the Hilal Visibility Globe and select a date, the map of the world is colored according to these zones. Each point on the globe is evaluated based on the physical parameters at that location: the angular separation of the Sun and Moon, the altitude of the Moon above the horizon at sunset, and the width of the crescent.

When you see green (Zone A), it means the crescent should be clearly visible to any observer with normal eyesight and a clear horizon. Zone B (darker green) means visibility under perfect conditions. Zone C (orange) means optical aid may help you locate it, after which the naked eye can follow.

When you see Zone E (the outermost colored band), it means: the Moon is above the horizon after sunset, the conjunction has occurred, the crescent is geometrically “born” — but no empirical model predicts that anyone can see it. Out of hundreds of documented attempts under similar conditions, no one has succeeded.

And beyond Zone E, the map goes unmarked — the conjunction has not yet occurred, or the Moon has already set. There is no crescent at all. Not even in principle.

If you switch to other criteria in the app — Yallop, Shaukat, SAAO, or Istanbul 1978 — you will also see Zone D (red), representing the narrow territory where only optical aid (telescopes, binoculars) might detect the crescent. Some of these criteria also enforce the Danjon limit explicitly: below approximately 7° of elongation between Sun and Moon, the crescent is marked as impossible regardless of equipment.

The critical boundary is between the colored zones and the unmarked region. Everything within the colored zones is a matter of difficulty — ranging from easy (Zone A) to extremely challenging (Zone E). The unmarked region is a matter of impossibility — there is nothing to see.

When someone claims to have sighted the crescent at a location and time that falls in the unmarked region of the map — or even deep in Zone E — they are claiming to have seen something that no one in the entire documented history of crescent observation has ever seen under comparable conditions. The witness may be sincere, but what they saw was not the hilal.

Applying This to the Fiqh

With this understanding, let us return to the two positions and see how they interact with what we now know.

What We Are NOT Saying

We are not saying that calculation should replace ruʾyah. The month begins with sighting, not with a computer prediction. If the criteria say “Zone C — may need optical aid” and an experienced observer with excellent eyesight sees the crescent with the naked eye, that sighting is valid. The criteria are empirical models with margins of uncertainty in the middle zones.

We are not saying that every Muslim must consult an astronomer before going out to look for the crescent. Moon sighting should remain a communal, accessible practice.

We are not saying that the testimony of a Muslim is unimportant. It is sacred, and rejecting it without basis is a grave matter.

What We ARE Saying

We are saying that when a sighting is claimed under conditions where the map is unmarked — where no crescent exists, or where the location falls deep in Zone E where no observation has ever succeeded — the claim is necessarily mistaken, regardless of the sincerity of the witness.

We are saying that this is not “preferring calculation over sighting.” It is recognizing that what was reportedly “sighted” was not the hilal. The witness may have seen something — but it was not the new crescent moon.

We are saying that this falls under the established Islamic principle of evaluating testimony against known impossibility — the same principle that Ibn al-Jawzī articulated when he said that the trustworthiness of witnesses is of no use when they report something impossible.

We are saying that Ibn Taymiyyah himself — the scholar most frequently cited against this position — actually affirmed empirical astronomical knowledge as valid, used astronomical reasoning in his own legal analysis, and criticized those who rejected all astronomical knowledge out of ignorance.

The Two Questions Are Different

The confusion in this debate arises from conflating two distinct questions:

These are fundamentally different questions. The first asks what triggers the legal obligation. The second asks whether a reported observation matches physical reality. Answering “yes” to the second does not change the answer to the first.

Obedience to Authority and Where Responsibility Falls

Everything discussed so far — visibility criteria, the Danjon limit, the distinction between impossibility and speculation — concerns the knowledge side of the question. But there is an equally important practical side that every Muslim needs to understand: What do I do if my authority declares a sighting that I know is impossible?

In a Muslim Country: Follow the Ruler

The answer, according to Islamic law, is clear: you follow the authority, and the responsibility for any error falls on them, not on you.

The Prophet ﷺ said:

الإِمَامُ ضَامِنٌ وَالْمُؤَذِّنُ مُؤْتَمَنٌ اللَّهُمَّ أَرْشِدِ الأَئِمَّةَ وَاغْفِرْ لِلْمُؤَذِّنِينَ

“The imam is a guarantor and the muʾadhdhin is entrusted. O Allah, guide the imams and forgive the muʾadhdhins.” — Ṣaḥīḥ Abū Dāwūd, no. 517 (authenticated by Shaykh al-Albānī)

The imam — here meaning the leader, the authority — bears the responsibility (ḍāmin). He is the guarantor. If he makes the right call, the community benefits. If he errs, the burden is his.

Ibn Taymiyyah addresses this exact scenario directly. Someone poses the objection: what if the imam who is entrusted with confirming the crescent sighting is negligent — perhaps by rejecting the testimony of upright witnesses, or by relying on an astrologer’s claim that the crescent could not be seen? Ibn Taymiyyah answers:

مَا يَثْبُتُ مِنْ الْحُكْمِ لَا يَخْتَلِفُ الْحَالُ فِيهِ بَيْنَ الَّذِي يُؤْتَمُّ بِهِ فِي رُؤْيَةِ الْهِلَالِ مُجْتَهِدًا مُصِيبًا كَانَ أَوْ مُخْطِئًا أَوْ مُفَرِّطًا

“The ruling that is established does not change depending on whether the authority who is followed in the matter of crescent sighting was exercising ijtihad correctly, or was mistaken, or was negligent.”

He then cites the hadith from the Sahih:

يُصَلُّونَ لَكُمْ فَإِنْ أَصَابُوا فَلَكُمْ وَلَهُمْ وَإِنْ أَخْطَئُوا فَلَكُمْ وَعَلَيْهِمْ

“They [the imams] pray for you; if they do right, the reward is for you and for them; if they err, the reward is for you and the burden is upon them.”

And he concludes:

فَخَطَؤُهُ وَتَفْرِيطُهُ عَلَيْهِ لَا عَلَى الْمُسْلِمِينَ الَّذِينَ لَمْ يُفَرِّطُوا وَلَمْ يُخْطِئُوا

“His error and his negligence fall upon him, not upon the Muslims who themselves were neither negligent nor mistaken.”

— Majmūʿ al-Fatāwā, 25/206

This is a principle of immense practical importance. In a Muslim country with an established authority responsible for hilal determination — whether a government ministry, a royal court, or an official sighting committee — the individual Muslim follows their declaration. If that authority accepts a sighting that was astronomically impossible, the individual Muslim who followed the declaration in good faith bears no sin. The accountability is on the authority that made the erroneous decision.

This does not mean the authority should accept impossible sightings — on the contrary, the entire weight of this article argues that they should use every available tool, including visibility criteria, to ensure their decisions are sound. The authority bears a heavy trust (amānah), and accepting false sightings is a failure of that trust. But the individual Muslim is not required to rebel against the authority’s decision or fast separately in secret.

In Non-Muslim Countries: A More Complex Reality

The situation in countries without a central Islamic authority is more nuanced. Muslims in the West and other non-Muslim-majority countries face a fragmented landscape. There is no single qāḍī or official body that all Muslims recognize.

In practice, Muslims in these contexts may follow different authorities:

• Some follow a local Islamic council or mosque committee that conducts its own sighting or applies visibility criteria for their region.
• Some follow the decision of their country of origin — a Pakistani community in the UK may follow Pakistan’s announcement, Turkish Muslims in France may follow the Turkish Diyanet’s declaration, and so on — because they recognize the authority of that government’s religious leadership as their representative in matters of worship.
• Some follow international bodies such as the Fiqh Council of North America or the European Council for Fatwa and Research, which have adopted calculation-based or criteria-based approaches.
• Some follow Saudi Arabia’s announcement for one or both Eids, following the principle of ittiḥād al-matāliʿ or out of a desire for unity with the Ḥaramayn.

Each of these choices reflects a decision about who constitutes the authority — and the same principle applies: once you have recognized a legitimate authority, you follow their decision, and the responsibility for any error is theirs.

The key insight is that this question — who is my authority? — is prior to and separate from the question of visibility criteria. The visibility criteria help the authority make a sound decision. The individual Muslim’s obligation is to follow a recognized authority and to encourage that authority to use the best available knowledge — including astronomical data — to fulfill the trust placed in them.

What This Means for the App

The Hilal Visibility Globe does not tell you when to fast or when to celebrate Eid. That is the role of your authority. What the app does is give you — and your authority — the information needed to evaluate sighting claims. If your authority declares a sighting, you follow it. But if you are part of a sighting committee, an Islamic council, or any body responsible for making that decision, the app gives you the tools to make that decision responsibly, in accordance with both the Sunnah and the physical reality that Allah has placed in His creation.

To Those Who Reject All Astronomical Input

Your concern is valid. The Sunnah must be preserved. The simplicity of ruʾyah — going out, looking with your eyes, seeing the crescent — is a beautiful act of worship that connects every generation of Muslims back to the time of the Prophet ﷺ. No one should take this away.

But consider: when Ibn Taymiyyah himself looked at the western horizon and reasoned that if the crescent is seen in the East, it must be visible in the West because “it increases in brightness and distance from the Sun” — he was using the same astronomical principles that these criteria are built upon. He called this amr maḥsūs — observable reality.

The criteria are not replacing your eyes. They are telling you what your eyes cannot see: whether a crescent exists to be looked for in the first place.

And consider the harm of the opposite: if we accept every claimed sighting without any verification, including claims made under physically impossible conditions, we risk beginning Ramadan or celebrating Eid on the wrong day. This is not protecting the Sunnah. It is introducing error into worship.

To Those Who Use Visibility Criteria

Your commitment to accuracy is important. But remember that these criteria are empirical models, not divine revelation. They are built from human observations and have margins of uncertainty. In the marginal zones (B, C, D), sightings that seem unlikely can and do occur. Be careful not to reject valid testimony simply because it seems improbable. Improbable and impossible are not the same thing.

Use the criteria where they are certain — in Zone F, where impossibility is established. Be humble where they are uncertain — in the marginal zones where human experience and atmospheric conditions vary.

And always maintain respect for those who disagree. This is a matter of ijtihad among sincere scholars, not a matter of faith versus disbelief.

Conclusion

The hilal visibility question is not a battle between faith and science. It is a question about how we apply well-established Islamic principles — ruʾyah, shahādah, evaluation of testimony, and recognition of physical reality — in a time when our understanding of the physical world is far more detailed than it was in the 7th century.

The Prophet ﷺ told us to fast upon sighting the crescent. He did not tell us to fast upon someone claiming to have sighted the crescent when the crescent cannot exist. The command presupposes that what is sighted is real.

Ibn Taymiyyah condemned the speculative calculator who overrides valid testimony. He did not argue that we must accept claims of seeing what is physically absent.

The tools we have today — including visibility criteria and apps that show you exactly where and when sighting is possible — are not replacements for ruʾyah. They are aids that help us understand what we are looking at, verify what we are told, and worship Allah with greater accuracy and confidence.

When you open the app and see the zones spread across the globe, you are looking at the accumulated knowledge of centuries of Muslim and non-Muslim observers, formalized into a framework that protects the integrity of the lunar calendar.

That is not calculation replacing sighting. That is knowledge serving worship.

References

Primary Islamic Sources

• Ibn Taymiyyah, Majmūʿ al-Fatāwā, 25/104 — kutub.io/en/book/7289/12552
• Ibn Taymiyyah, Majmūʿ al-Fatāwā, 25/132 — kutub.io/en/book/7289/12580
• Ibn Taymiyyah, Majmūʿ al-Fatāwā, 25/133 — kutub.io/en/book/7289/12581
• Ibn Taymiyyah, Majmūʿ al-Fatāwā, 25/206 — kutub.io/en/book/7289/12654
• Ibn Taymiyyah, Al-Radd ʿalā al-Manṭiqiyyīn, p. 363 — kutub.io/en/book/7626/364
• Ibn Taymiyyah, Al-Radd ʿalā al-Manṭiqiyyīn, p. 386 — kutub.io/en/book/7626/387
• Ibn Taymiyyah, Al-Radd ʿalā al-Manṭiqiyyīn, p. 387 — kutub.io/en/book/7626/388
• Ibn al-Jawzī, al-Mawḍūʿāt, 1/106
• Sahih al-Bukhari, hadith no. 1909
• Sahih Muslim, hadith no. 1081
• Ṣaḥīḥ Abū Dāwūd, hadith no. 517 (authenticated by al-Albānī)
• Al-Mawsūʿah al-Fiqhiyyah al-Kuwaytiyyah, “Ruʾyat al-Hilāl”, vol. 22 - kutub.io/en/book/11430/13156

Scholars on Calculation and Crescent Determination

• Ibn Surayj (d. 306/918): recorded in al-Nawawī, al-Majmūʿ 6/235; Ibn Ḥajar, Fatḥ al-Bārī 4/123; al-ʿIrāqī, Ṭarḥ al-Tathrīb 4/112-113
• Taqī al-Dīn al-Subkī (d. 756/1355), Al-ʿIlm al-Manshūr fī Ithbāt al-Shuhūr, pp. 20-22; Fatāwā al-Subkī 1/209-210
• Al-Qarāfī (d. 684/1285): recorded in al-Mawsūʿah al-Fiqhiyyah al-Kuwaytiyyah, vol. 22, pp. 31-34
• Al-Zarkashī (d. 794/1392): recorded in al-Mawsūʿah al-Fiqhiyyah al-Kuwaytiyyah, vol. 22, pp. 31-34
• Al-Qalyūbī (d. 1069/1659), Ḥāshiyat al-Qalyūbī ʿalā Sharḥ al-Maḥallī; also in al-Mawsūʿah al-Fiqhiyyah al-Kuwaytiyyah, vol. 22, pp. 36-38
• Muḥammad al-Ramlī (d. 1004/1596), Nihāyat al-Muḥtāj ilā Sharḥ al-Minhāj; discussed in ʿUmar ibn al-Ḥabīb al-Ḥusaynī, Fatḥ al-ʿAlī fī Jamʿ al-Khilāf bayna Ibn Ḥajar wa-Ibn al-Ramlī (Jeddah: Dār al-Minhāj, 2010), pp. 819-822

Fiqh of Matāliʿ

• Ibn ʿĀbidīn, Radd al-Muḥtār - kutub.io/en/book/21613/1049
• Imam al-Nawawī, al-Majmūʿ - kutub.io/en/book/2186/3179

Astronomical Sources

• Odeh, M. Sh. (2006), “New Criterion for Lunar Crescent Visibility” — astronomycenter.net
• Yallop, B.D. (1997), “A Method for Predicting the First Sighting of New Crescent Moon” — NAO Technical Note No. 69
• ICOP World Record Observations — astronomycenter.net/record.html
• Danjon, A. (1936), “Le croissant lunaire”
• Schaefer, B.E. (1996), “Lunar Crescent Visibility” — QJRAS 37