MUHAMMADIYAH.OR.ID, MEDAN—A leading Muhammadiyah astronomy expert has responded to criticism surrounding the Global Unified Hijri Calendar (Kalender Hijriah Global Tunggal/KHGT) and comparisons with Turkey’s Diyanet calendar, calling for a more comprehensive and less selective analysis.
Arwin Juli Rakhmadi Butarbutar, a falak (Islamic astronomy) specialist at Muhammadiyah’s Tarjih and Tajdid Council, addressed the debate in an article published Thursday (08/01) by the Falak Observatory of the Muhammadiyah University of North Sumatra, His response followed a critique by an astronomer affiliated with Indonesia’s National Research and Innovation Agency and the Ministry of Religious Affairs.
Arwin welcomed the critic’s serious engagement with KHGT, particularly the discussion on the projected start of Ramadan 1447 H in mid-February. However. he questioned the narrow focus on a single month and a single map, noting that Muhammadiyah’s assessment involved cross-month analysis and long-term evaluation.
Vulnerabilities and Evaluation
KHGT, he said, remains open to testing and criticism, given its recent implementation. He reiterated earlier warnings about its vulnerabilities such as defining the start of a day and the transfer of visibility criteria. Still, he argued that such complexities require broad analysis rather than partial judgement.
Addressing the Turkish Diyanet map, Arwin said Muhammadiyah had also identified issues, particularly inconsistencies in Turkey’s use of geocentric and topocentric approaches. These inconsistencies, he added, reinforced Muhammadiyah’s preference for a geocentric model.
He rejected claims that Muhammadiyah had misread the outcomes of the 2016 Turkey Conference, noting that official documents did not explicitly mandate their approach. While acknowledging differing scientific opinions, Arwin urged critics to avoid tendentious language and to frame disagreements with academic rigor and openness. (Bintang Adrian)
