Why, according to astronomical calculation, the Government and Nahdlatul Ulama determine it on Saturday, while Muhammadiyah sets it on Friday?
As the month of Ramadan approaches its end, a question that frequently arises in society is: When will Eid al-Fitr be celebrated? For the year 1447 Hijri, the potential for differences appears once again. Some Muslims in Indonesia will celebrate Eid al-Fitr 1447 H on Friday Legi, March 20, 2026, while others will observe it on Saturday Pahing, March 21, 2026.
This difference is not merely a matter of organizational affiliation, but rather stems from differing methodological approaches in determining the beginning of the Hijri month. In Indonesia, these approaches are reflected in the methods used by the Ministry of Religious Affairs of the Republic of Indonesia as the state authority, Nahdlatul Ulama as the largest Islamic organization emphasizing moon sighting supported by contemporary calculations, and Muhammadiyah, which adopts a global calendar system based on astronomical calculations.
Government of Indonesia: Isbat Session and the New MABIMS Criteria
The determination of the beginning of the Hijri month by the government is conducted through an isbat session organized by the Ministry of Religious Affairs. This mechanism integrates two primary approaches in Islamic astronomy: hisab (astronomical calculation) and rukyat hilal (crescent moon observation).
As a scientific parameter for crescent visibility, the government applies the New MABIMS criteria, namely:
Minimum الهلال altitude: 3°
Minimum elongation: 6.4°
Contemporary astronomical calculations (hisab haqiqi bit-tahqiq) indicate that on the observation date, Thursday, March 19, 2026, the crescent’s position in Indonesia remains relatively low.
In western regions such as Banda Aceh, the crescent altitude is approximately 3.05° with an elongation of about 6.1°. In Jakarta, it is around 1.8° with elongation 5.7%, in Semarang about 1.7° with elongation 5.5°, and in eastern regions such as Jayapura, about 1.1° with elongation 4.5°.
Based on the New MABIMS criteria, elongation values across Indonesia remain below the 6.4° threshold. This indicates that astronomically, the crescent is in a very low visibility phase, making actual observation extremely difficult. Under such conditions, if no valid sighting report is confirmed, Ramadan is completed to 30 days (istikmal), resulting in Eid al-Fitr falling on Saturday, March 21, 2026 (as determined through the government’s isbat session).
Nahdlatul Ulama: Moon Sighting Supported by Astronomical Calculation
Nahdlatul Ulama’s approach is fundamentally based on rukyatul hilal (crescent observation), as derived from Prophetic traditions regarding the determination of lunar months. However, in practice, NU also utilizes contemporary astronomical calculations as a scientific tool to predict the moon’s position and assess its visibility.
This scientific reinforcement was emphasized in the 34th NU Congress, encouraging the integration of Islamic astronomy in determining worship times. Technically, it is implemented through the criteria issued by the NU Falakiyah Institute (IRNU), which stipulate:
Minimum الهلال altitude: 3°
Minimum elongation: 6.4°
These parameters are essentially identical to the New MABIMS criteria used by the government. Therefore, methodologically, NU’s determination aligns closely with that of the government. Given that elongation values across Indonesia remain below 6.4°, the possibility of crescent visibility is extremely low. If no valid and scientifically accountable sighting is obtained, the decision follows istikmal, completing Ramadan to 30 days, thus placing Eid al-Fitr on Saturday Pahing, March 21, 2026.
Muhammadiyah: Global Hijri Calendar (KHGT)
Meanwhile, Muhammadiyah employs a global astronomical calculation approach through the Global Hijri Calendar (KHGT).
According to the official decree of Muhammadiyah’s Central Board, 1 Shawwal 1447 H is set to fall on Friday, March 20, 2026.
Within the KHGT system, the beginning of the month is determined globally using the following parameters:
Minimum الهلال altitude: 5°
Minimum elongation: 8°
If before 24:00 UTC there exists any region on Earth where these criteria are fulfilled, the new month is declared globally. Based on astronomical data, such conditions are met in certain regions, for example:
Latitude: 64° 59′ 57.47″ N
Longitude: 42° 03′ 3.47″ E
Moon altitude: +06° 29′ 20″
Elongation: 08° 00′ 00″
Based on this calculation, Muhammadiyah determines that 1 Shawwal 1447 H falls on Friday Legi, March 20, 2026.
Strengthening Unity, Embracing Differences
Differences in determining the beginning of the Hijri month are essentially part of scholarly ijtihad within Islamic astronomy. Therefore, such differences should not be viewed as a source of division, but rather as a reflection of intellectual diversity deeply rooted in Islamic tradition.
However, within the context of national life, Indonesian Muslims also bear the responsibility of maintaining unity and social order. This highlights the importance of the government’s isbat decision, which involves scholars, astronomers, representatives of Islamic organizations, and state institutions, ensuring that the outcome reflects a collective consideration of religious, scientific, and social aspects.
Following the government’s decision does not negate differing scholarly opinions; rather, it represents religious maturity and a commitment to the greater common good. With a unified national reference, Muslims can celebrate religious holidays more collectively, fostering social harmony and togetherness.
Thus, while respecting diverse scholarly perspectives, supporting and adhering to the government’s decision can be seen as a noble effort to preserve unity and move toward the unification of the Hijri calendar in Indonesia.
Dr. Misbah Khusurur, S.H.I., M.S.I.
Lecturer in Islamic Astronomy, Dean of FKI UNUGHA Cilacap