Global Hijri Calendar Faces Indonesian Skepticism

A new global Islamic calendar is stirring debate, with a prominent Indonesian astronomer raising concerns. The Single Global Hijri Calendar, championed by Turkey, could create more discrepancies for those observing in Indonesia, possibly leading to confusion among Muslims worldwide.

Contrasting Calendars

**Thomas Djamaluddin**, an astronomy and astrophysics professor at the National Research and Innovation Agency (BRIN), has voiced his criticism of the Single Global Hijri Calendar. He argues it favors calculations over visual sightings, potentially causing significant date differences.

The KHGT (Single Global Hijri Calendar) is scheduled to launch in 1447 Hijriah, beginning with 1 Muharram. **Djamaluddin** stated that this calendar’s implementation will be tested in determining the start of Ramadan.

The Indonesian government and most Islamic organizations employ criteria agreed upon by religious affairs ministers from Indonesia, Malaysia, Brunei Darussalam, and Singapore (Mabims). According to the KHGT, the new Islamic year 1447 Hijriah commenced on June 26, 2025. However, the Indonesian government designated June 27, 2025, as a national holiday.

The divergence in dates arises from differing criteria. The position of the new crescent moon on June 25, 2025, in Southeast Asia did not meet Mabims’ criteria. Conversely, the Turkish criteria, or KHGT, indicated that the moon’s position met the requirements. Conjunction occurred before dawn in New Zealand, marking the beginning of the Islamic year on June 26, 2025.

Global vs. Local Observance

The KHGT’s concept of a day aligns with **Jamaluddin Abdur Razzaq**’s proposal from Morocco: the day begins globally at midnight, around the International Date Line. **Djamaluddin** indicated that differences could also surface in determining the start of the fasting month of Ramadan.

Muhammadiyah, an Islamic organization using the Global Hijri Calendar, responded via its official website. They contend that the KHGT can compel specific regions into a new month even if a crescent moon has not been sighted. Conversely, it might delay other regions that have already sighted the moon for the sake of global uniformity, particularly when the moon is below the horizon in eastern regions.

According to **Arwin Juli Rakhmadi Butar-butar**, a Muhammadiyah astronomy expert, crescent phases are global occurrences, while sightings are local. He posits that even if a crescent is unseen in one region due to its position below the horizon, it still exists astronomically following conjunction (ijtima’).

“Even if the crescent is not visible in a certain region due to its position below the horizon, astronomically the crescent still exists after the conjunction (ijtima’),” said **Arwin Juli Rakhmadi Butar-butar**.

Changes in moon phases are related to elongation, the angular distance between the Sun and Moon. Following conjunction, elongation grows, and a crescent initially below the horizon in one region becomes visible elsewhere. If a sighting is possible somewhere, the crescent is globally considered present, even if the moon is below the horizon in other regions.

A 2023 study from Pew Research Center showed that nearly half (48%) of the world’s Muslim population does not observe the beginning of religious holidays based on visual sighting. They base it on astronomical calculations.

The contrasting approaches to the Hijri calendar highlight the different methodologies and considerations that shape religious observance. With calculations versus visual sightings, it remains to be seen which system gains broader acceptance.