Every year, the same question divides Muslim communities worldwide: has the new crescent moon been sighted? The answer determines when Ramadan begins, when it ends, when Eid is celebrated and how the entire Islamic Hijri calendar operates. It sounds like a simple observational question. It is anything but.
Why the Crescent Matters
The Islamic calendar is purely lunar: twelve months of 29 or 30 days each, with no solar correction. Each month begins when the thin crescent moon (hilal) is first sighted after a new moon. This is not a modern simplification. It traces directly to Quranic instruction and prophetic tradition. The Prophet Muhammad said "Fast when you see it [the crescent] and break your fast when you see it," establishing physical observation as the basis for determining months.
The crescent that marks the start of a new month is extraordinarily thin - sometimes less than 1% illuminated. It appears low on the western horizon just after sunset and is visible for only a brief window, sometimes as short as 15 minutes. Cloud cover, haze, light pollution or simply a crescent too thin to detect with the naked eye can make sighting impossible even when the moon is technically above the horizon.
The Three Schools of Thought
Local Sighting (Ikhtilaf al-Matali)
Each region or country determines its own calendar based on local observation. If the crescent is sighted in Morocco, it does not affect the calendar in Indonesia. This was the historical practice for centuries when communication between distant Muslim communities was slow or nonexistent, and each city or region naturally operated on its own sighting.
The strength of this approach is its adherence to the literal instruction of observing the crescent. Its complication is that neighbouring countries - sometimes even neighbouring cities - may begin Ramadan on different days. Pakistan and India, sharing a border, have started Ramadan on different days in most recent years.
Global Sighting (Ittihad al-Matali)
If the crescent is reliably sighted anywhere in the world, all Muslims should begin the month. This position argues for unity: there is one moon, one ummah (global community) and one Ramadan. Saudi Arabia's sighting, given its proximity to Mecca, often carries particular weight in this approach.
The practical challenge is verification. A sighting claim from one country must be communicated to others rapidly and accepted as reliable. This has led to controversies where Saudi Arabia announced a sighting that astronomers said was physically impossible given the moon's position at that time and location.
Astronomical Calculation (Hisab)
The moon's orbit is precisely known. The moment of conjunction (new moon), the angle of the crescent, its altitude above the horizon at sunset and its visibility can all be calculated years in advance. Proponents argue that calculation fulfils the spirit of the prophetic instruction by determining when the crescent could be seen, even if clouds prevent actual observation.
Turkey, much of Southeast Asia and many Muslim communities in Europe and North America use calculation-based calendars. The Fiqh Council of North America adopted a calculated calendar in 2006, ending decades of last-minute uncertainty for American Muslims planning work schedules and school absences around Ramadan and Eid.
Why Neighbouring Countries Start on Different Days
The combination of local sighting practices, differing acceptance of Saudi announcements and varying adoption of calculation means that in any given year, Ramadan may begin on two or even three different days across the Muslim world. In 2023, most of the Middle East began Ramadan on March 23, while parts of South Asia, East Africa and some Western communities started on March 24.
The one or two day difference cascades through the month. If you start a day later, Eid al-Fitr (marking the end of Ramadan) also falls a day later. Families split across countries may find themselves celebrating on different days. Muslims living in multicultural cities sometimes see their own community divided, with one mosque observing Eid while the one across the street is still fasting.
The Science of Crescent Visibility
Astronomers can predict with near-perfect accuracy when the new moon (conjunction) occurs. But conjunction is not visibility. After conjunction, the moon continues in its orbit, gradually separating from the sun. The crescent only becomes visible once enough angular separation exists for the thin lit edge to be detectable against the twilight sky.
Several criteria affect visibility: the age of the moon since conjunction (typically at least 15-20 hours), the angular separation from the sun (at least 7-8 degrees), the altitude of the moon above the horizon at sunset (at least 5 degrees for naked-eye visibility) and atmospheric conditions. Astronomers have developed mathematical models - the most widely used being the Yallop criterion and the Odeh criterion - that predict crescent visibility as "easily visible," "visible under perfect conditions," "may need optical aid" or "not visible."
These models are highly accurate but not infallible. Exceptional observers with keen eyesight in pristine atmospheric conditions have occasionally reported sightings that models rated as impossible. Whether these reports reflect genuine observation or well-intentioned error is itself a source of disagreement.
The Saudi Factor
Saudi Arabia's crescent sighting announcements carry disproportionate influence because of Mecca's spiritual centrality. The Supreme Court of Saudi Arabia convenes sighting committees each month, and their announcements are broadcast immediately across the Muslim world. Many countries, particularly in the Gulf region and parts of Africa, follow Saudi declarations directly.
However, Saudi sighting announcements have sometimes conflicted with astronomical data. Multiple instances exist where Saudi authorities announced a sighting when astronomers calculated the crescent to be below the horizon or too thin to see from the reported location. These discrepancies have fuelled the debate rather than settled it, with each side interpreting the conflicts differently: sighting advocates attribute the anomalies to God's will or exceptional observers, while calculation advocates see them as evidence that human claims are unreliable.
Digital Age Complications
Social media has added a new layer. Crescent sighting claims now spread globally within minutes, complete with photographs. But smartphone cameras can produce artefacts that resemble a crescent, and thin cloud formations near the horizon have been mistaken for the hilal. Verification of photographic evidence has become a discipline in itself, with astronomers examining EXIF data, checking the moon's calculated position against the image composition and analysing whether the alleged crescent's orientation matches what physics predicts.
At the same time, digital communication has made the practical argument for calculation stronger. When the start of Ramadan can be announced months in advance with scientific certainty, the logistical benefits are substantial: schools, employers, airlines, hospitals and governments can plan accordingly. The counter-argument is that convenience should not override religious methodology, and that the act of looking for the crescent is itself a form of worship and connection to tradition.
The crescent moon debate is unlikely to reach global consensus. It touches theology, astronomy, cultural identity, institutional authority and the tension between tradition and modernity simultaneously. What makes it remarkable is that the question at its centre - can you see a sliver of reflected sunlight on a rock 384,400 kilometres away - has been asked every month for over 1,400 years and still does not have one answer that satisfies everyone who asks it.