BRIN Highlights Weaknesses in Single Global Hijri Calendar Concept for Determining Start of Ramadan
Jakarta, VIVA – Rhorom Priyatikanto, an astronomy researcher at the National Research and Innovation Agency (BRIN), has highlighted a number of weaknesses in the Single Global Hijri Calendar (KHGT) concept as it applies to determining the start of Ramadan in Indonesia. One of the principal issues is the determination of global boundary lines, which he considers do not fully represent the astronomical and geographical conditions of various regions worldwide.
According to Rhorom, the global Islamic calendar concept establishes a single Hijri date for the entire world based on hilal (new crescent moon) visibility in a designated reference area. However, this approach still gives rise to problems when applied in regions with differing observation conditions, such as Indonesia.
"Firstly, the weakness of the Single Global Hijri Calendar lies in the determination of reference lines, which still require re-examination," Rhorom said.
He cited the case of this year's start of Ramadan, when the hilal was globally deemed potentially visible in certain areas such as Alaska. Under the global calendar scheme, this condition would theoretically allow the entire world to enter the new Hijri month. Yet in Indonesia, the position and visibility of the hilal were considered still far from meeting the criteria for the start of Ramadan.
"Take this Ramadan as an example — if the hilal is already visible in Alaska, then theoretically everyone could begin, but many parts of Indonesia assess that conditions are still far from the beginning of Ramadan, giving rise to doubt," he said.
Rhorom argued that the selection of boundary lines and the matla (reference area for hilal visibility) in the global calendar still needs to be reviewed so as to accommodate a greater range of conditions faced by Muslims across the world.
"The selection of boundary lines and matla that are clearer and accommodate as many Muslims as possible must be considered," he said.
In Indonesia, the Single Global Hijri Calendar concept is notably employed by the Islamic organisation Muhammadiyah through its global hisab (astronomical calculation) method. Meanwhile, the government, through the Ministry of Religious Affairs, uses the MABIMS imkanur rukyat criteria, which combine astronomical calculations with regional hilal observation across Southeast Asia.
Beyond the issue of global boundary lines, Rhorom also assessed that the development of Islamic calendar criteria, including imkanur rukyat, still requires the strengthening of local hilal observation databases. Indonesia's atmospheric conditions — which are more humid, cloudy, and naturally hazy — make hilal visibility near the horizon more difficult compared with desert or subtropical regions.
According to Rhorom, the global Islamic calendar concept establishes a single Hijri date for the entire world based on hilal (new crescent moon) visibility in a designated reference area. However, this approach still gives rise to problems when applied in regions with differing observation conditions, such as Indonesia.
"Firstly, the weakness of the Single Global Hijri Calendar lies in the determination of reference lines, which still require re-examination," Rhorom said.
He cited the case of this year's start of Ramadan, when the hilal was globally deemed potentially visible in certain areas such as Alaska. Under the global calendar scheme, this condition would theoretically allow the entire world to enter the new Hijri month. Yet in Indonesia, the position and visibility of the hilal were considered still far from meeting the criteria for the start of Ramadan.
"Take this Ramadan as an example — if the hilal is already visible in Alaska, then theoretically everyone could begin, but many parts of Indonesia assess that conditions are still far from the beginning of Ramadan, giving rise to doubt," he said.
Rhorom argued that the selection of boundary lines and the matla (reference area for hilal visibility) in the global calendar still needs to be reviewed so as to accommodate a greater range of conditions faced by Muslims across the world.
"The selection of boundary lines and matla that are clearer and accommodate as many Muslims as possible must be considered," he said.
In Indonesia, the Single Global Hijri Calendar concept is notably employed by the Islamic organisation Muhammadiyah through its global hisab (astronomical calculation) method. Meanwhile, the government, through the Ministry of Religious Affairs, uses the MABIMS imkanur rukyat criteria, which combine astronomical calculations with regional hilal observation across Southeast Asia.
Beyond the issue of global boundary lines, Rhorom also assessed that the development of Islamic calendar criteria, including imkanur rukyat, still requires the strengthening of local hilal observation databases. Indonesia's atmospheric conditions — which are more humid, cloudy, and naturally hazy — make hilal visibility near the horizon more difficult compared with desert or subtropical regions.