How Saudi Arabia Decides Islamic Dates: The Moon-Sighting Process
Saudi Arabia doesn’t set the start of each Hijri month by consulting an astronomer’s chart alone — it relies on people physically looking for the moon. The process is called moon sighting (ru’yah), and it’s the reason Islamic dates in the kingdom sometimes shift by a day compared to what an app’s calculated calendar shows.
The basic mechanism
Every Hijri month is either 29 or 30 days long, and which one it turns out to be depends on whether the new crescent moon (hilal) is sighted on the evening of the 29th day. If it’s sighted, the new month begins the next day. If it isn’t — whether because the moon genuinely isn’t visible yet or because clouds and haze got in the way — the current month is simply extended to 30 days, and the new month starts the day after that instead.
Who actually does the sighting
In Saudi Arabia, this responsibility sits with the Supreme Court, which coordinates a network of official observers and moon-sighting committees stationed at various points around the country. On the 29th evening of the current month, these observers scan the western horizon just after sunset, the narrow window when a new crescent — if it exists and is visible — would appear low in the sky before setting shortly after the sun.
Testimony from credible witnesses who report a sighting is submitted to the court, which then evaluates it and issues an official ruling and public announcement — typically that same night or very early the next morning.
Why calculation alone isn’t used
Modern astronomy can calculate exactly when a new moon occurs (the point of conjunction) and can predict, with a high degree of confidence, whether the resulting crescent will be visible from a given location. Saudi Arabia and many other Muslim-majority countries still prioritize actual sighting over calculation, following the traditional understanding of hadith instructing Muslims to fast and break their fast based on sighting the moon. Astronomical prediction is used as a planning tool and cross-check, but it doesn’t override a confirmed physical sighting or override the need for one.
Why this occasionally creates confusion
Because visibility depends on real, local, and sometimes marginal conditions, it’s possible for the crescent to be reported as sighted in one location and not another on the same evening — which is one reason different countries occasionally announce a month starting a day apart. It’s also why online calendars and apps that rely purely on calculated projections can show a date that’s a day ahead of or behind the officially announced one; those tools are forecasting what should be visible, not reporting what was actually confirmed.
Frequently asked questions
Does Saudi Arabia use calculation or sighting?
Sighting is the deciding factor; calculation is used for prediction and verification, not as the final word.
What happens if the moon isn’t sighted?
The current month is extended to 30 days by default, and the new month begins the day after.
Why do calendar apps sometimes show a different date than the official announcement?
Because most apps calculate dates in advance using astronomical projections, while Saudi Arabia’s official date depends on a real-time sighting report that can confirm or contradict that projection.
