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What are the Shariah-recognized methods for determining the beginning of the month, and what is the ruling on relying on astronomical calculations?

All praise is due to Allah, and prayers and peace be upon the Messenger of Allah. To proceed:

The beginning of the Month of Ramadan in the Shariah is established by one of two well-defined means, and there is no third alternative. These two methods are indicated by the Sunnah, and scholars have reached consensus on them:

First: Sightings of the Crescent

The primary basis for the commencement of the month is the sighting of the crescent. As the Prophet ﷺ said, in the well-authenticated Hadith agreed upon by both al-Bukhari and Muslim, reported from Ibn Umar (may Allah be pleased with them both): "If you see it, then fast; and if you see it, then break your fast."

Thus, the obligation of fasting and breaking the fast is dependent upon the sighting. This is a clear and decisive indication that sighting is the legally recognized cause.

Scholars have unanimously agreed that the start of the month is confirmed by sighting, and this consensus has been reported by many scholars, including Ibn Qudamah, may Allah have mercy on him.

According to the correct opinion, it suffices that one just and trustworthy Muslim sees it, provided the sighting is verified and approved by the ruler or his delegated judges. This is based on the report that Ibn Umar (may Allah be pleased with him) informed the Prophet ﷺ that he had seen the crescent, and the Prophet ﷺ fasted and commanded the people to fast.

It is a condition that the person who sights the crescent must be just; the testimony of a non-just person is not accepted in this matter.

Second: Completing Thirty Days of Sha‘ban

If the Muslims attempt to sight the crescent and do not see it, or if clouds, dust, or similar obstacles prevent its sighting, then they complete thirty days of Sha‘ban. This is based on the saying of the Prophet ﷺ: "If it is obscured from you, then complete the month of Sha‘ban to thirty days."

Consensus has also been reported on this matter. Therefore, the beginning of the month is established only by these two methods in Shariah.

Ruling on Relying on Astronomical Calculations

As for relying on astronomical calculations to establish the beginning of the month, this is not legally recognized in Shariah for several reasons:

  1. The Prophet ﷺ and his companions did not adopt astronomical calculations as a method, although they had the means to do so. Their abstention indicates that it is not to be relied upon, as acts of worship are to follow divine guidance, not human conjecture. Any attempt to adopt such a method is a newly invented innovation, as clarified by Shaykh al-Islam.

  2. The Prophetic texts link the ruling to sighting the crescent or completing the month; they do not link it to calculations.

  3. Scholars have unanimously ruled that astronomical calculations are not a valid basis for determining the beginning of the month. This consensus has been reported by Ibn Abd al-Barr, Shaykh al-Islam Ibn Taymiyyah, and Ibn Hajar, may Allah have mercy on them all.

Therefore, relying on calculations is a Bid’ah that contradicts both the Sunnah and scholarly consensus, and Muslims are not permitted to base their worship on it.

One must adhere to what is firmly established in Shariah without transgression or innovation.

We ask Allah, Glorified and Exalted, to guide us to follow His path, and to make us among those who adhere to the Sunnah, walking upon its guidance outwardly and inwardly. And Allah knows best. May Allah’s peace and blessings be upon our Prophet Muhammad ﷺ.