The proposal of a Unified Global Hijri Calendar continues to spark debate. While this effort aims to unify Muslims worldwide under a single lunar calendar, it has drawn criticism, especially from those who uphold traditional, local moon-sighting practices. Muhammadiyah, one of Indonesia’s largest Islamic organizations and a strong supporter of the unified global Hijri calendar, welcomes these criticisms as part of a healthy scholarly discourse.
One major concern raised by critics is that the the unified global Hijri calendar may require certain regions to begin a new lunar month even if the crescent moon (hilal) has not been physically sighted there, or to delay it in regions where it has, in order to maintain global uniformity. This is especially controversial in cases where the hilal is still below the horizon in eastern regions.
Such criticism generally emerges from a local sighting paradigm (rukyat) that the visible appearance of the moon is considered essential. In contrast, the unified global Hijri calendar relies on global astronomical calculations and the concept of a shared visibility zone (matlak), drawing on a different interpretation of both shar’i arguments and celestial events.
In traditional understanding, the hilal is the crescent moon that becomes visible after conjunction. However, classical fiqh literature doesn’t always delve into the scientific detail behind moon phases. This leaves room for clarification, especially for those who still prioritize local moon sightings.
According to Muhammadiyah’s astronomy expert, Arwin Juli Rakhmadi Butar-Butar, the scientific reasoning behind the unified global Hijri calendar can be summarized in three main arguments.
Lunar Phases as Global Phenomena
Lunar phases, including the emergence of the hilal, are global astronomical phenomena. The visibility of the crescent may vary by location, but its existence is not in question. Once the conjunction (ijtima’) occurs, the alignment of the sun and moon, the new moon technically begins, even if the hilal is still below the horizon and not visible to the naked eye. Arwin refers to Surah Yasin (36:39):
وَالْقَمَرَ قَدَّرْنَاهُ مَنَازِلَ حَتَّىٰ عَادَ كَالْعُرْجُونِ الْقَدِيمِ
“And the moon – We have determined for its phases, until it returns [appearing] like the old date stalk.
This interpretation suggests that the hilal exists as soon as the conjunction happens. Its visibility is a local issue, but its existence is global. Therefore, even if the crescent is below the horizon in some areas, the new month has technically begun.
Astronomical Dynamics and Elongation
The changing shape of the moon is related to elongation—the angular distance between the sun and the moon. This distance increases after conjunction, gradually making the crescent visible. This dynamic is referenced in Surah Yasin (36:40):
.لَا الشَّمْسُ يَنْبَغِي لَهَا أَنْ تُدْرِكَ الْقَمَرَ وَلَ اللَّيْلُ سَابِقُ النَّهَارِۚ وَكُلٌّ فِي فَلَكٍ يَسْبَحُونَ
“It is not for the sun to overtake the moon, nor does the night outstrip the day. And each is swimming in an orbit.”
As elongation increases, the moon that is initially invisible in one region will soon appear in others. Thus, if the crescent meets the visibility criteria (imkanu rukyat) in any part of the world, it should be considered valid globally, even for areas where it remains below the horizon.
Geographical Reality and Legal Precedent
Due to Earth’s rotation, western regions generally have a better chance of sighting the crescent than eastern ones. Islamic legal scholars (fuqaha) have long recognized this and stated that if the crescent is seen in the east, it applies to the west.
This reinforces the idea that a sighting in one part of the world can be accepted for others, aligning with the universal nature of lunar observations in rukyat hadiths.
From these perspectives, the unified global Hijri calendar is not only based on Islamic teachings but also in modern scientific understanding. Recognizing the crescent’s existence even when it’s not yet visible marks a shift from seeing the hilal as merely a local physical event to understanding it as a global astronomical reality.
This shift offers a practical and unifying solution for the Muslim world, where differing calendars often lead to disjointed observances of major religious events. The unified global Hijri calendar draws on the Prophet’s guidance that a lunar month lasts 29 or 30 days and is determined by the moon’s cycle, which is now accurately measurable through science.
Despite its confidence in the unified global Hijri calendar, Muhammadiyah remains open to further discussion and constructive feedback, in line with the Islamic tradition of ongoing inquiry and refinement.
Reference:
Butar-Butar, A. J. R. (2024, March). Hilal di bawah ufuk dalam KHGT. OIF UMSU. https://oif.umsu.ac.id/2024/03/hilal-di-bawah-ufuk-dalam-the-unified-global-hijri-calendar/
