Understanding the Hisab and Rukyat Methods in Determining Eid al-Adha by the Government
The determination of Eid al-Adha in Indonesia is always a moment eagerly anticipated by Muslims. The government, through the Ministry of Religion (Kemenag), uses two main methods to determine the beginning of Dzulhijjah, which then has implications for determining the day of Eid al-Adha, namely the hisab and rukyatul hilal methods. This synergy between astronomical calculations and field observations is carried out to ensure accuracy in accordance with Islamic Sharia principles.
Literally, hisab means calculation. In the context of determining the beginning of lunar months, hisab is a method of calculating the position of celestial bodies, especially the sun and moon, to determine the beginning of the month on the Hijri calendar.
This method relies on very precise astronomical data. Experts use mathematical formulas to determine when conjunction (ijtimak) or the position occurs when the earth, moon, and sun are in a straight line. In Indonesia, organizations such as Muhammadiyah generally use the Hisab Hakiki Wujudul Hilal criteria, where the new month begins if the hilal is already above the horizon at sunset, whatever its degree of altitude.
Rukyatul Hilal is the activity of observing the visibility of the hilal (new moon) directly in the field. This observation is carried out on the 29th day of the current month (29 Dzulkaidah) just after sunset.
If the hilal is seen by observers who have been sworn in, then that night is declared as the beginning of the new month. However, if the hilal is not visible due to weather factors or the position of the moon which is still too low, then the current month is completed to 30 days (istikmal). The Indonesian government deploys officers at hundreds of monitoring points from Aceh to Papua to carry out this process.
To bridge differences in results, Indonesia together with member countries of MABIMS (Ministers of Religion of Brunei Darussalam, Indonesia, Malaysia and Singapore) apply new criteria in determining the beginning of the Hijri month. These criteria are used as a reference in the Isbat Session:
These criteria are based on empirical data that the hilal is very difficult or impossible to see visually if it is below this figure. With these criteria, the hisab method is used as a guide (initial information), while rukyat is used as confirmation (factual verification).
The Isbat Session is the highest decision-making forum led by the Minister of Religion. The process is divided into three main stages:
This difference commonly occurs due to differences in matla (geographical legal area). The position of the moon in Saudi Arabia, which is further west, is often higher than in Indonesia at the same time.
Astronomically, hisab is very accurate in predicting the position of the moon. However, in certain fiqh traditions, eye observation (rukyat) is still needed as a form of worship and physical verification.
If the hilal is not visible at all monitoring points due to weather, then the government will carry out istikmal, which is to complete the month of Dzulkaidah to 30 days, so that the 1st of Dzulhijjah falls on the day after tomorrow.