As teh Islamic holy month of Ramadan approaches, Indonesia’s Ministry of Religious Affairs is preparing to determine its start date through a combination of astronomical calculations and visual sightings of the new crescent moon, known as the hilal.The Ministry has scheduled a meeting-a sidang isbat-for February 17, 2026, to analyze data provided by the Indonesian Agency for Meteorology, Climatology, and geophysics (BMKG) and consult wiht representatives from various Islamic organizations and astronomical experts. The outcome of this meeting will be crucial for Indonesia’s over 230 million Muslims as they prepare to begin the month of fasting and spiritual reflection.
Indonesia’s Ministry of Religious Affairs will hold a meeting on February 17 to determine the start of Ramadan 1447 H. As the Islamic holy month approaches, officials are looking to astronomical data to predict when the new crescent moon will appear.
The Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG) has released a report detailing its predictions for the visibility of the hilal, or crescent moon, which traditionally signifies the beginning of Ramadan. The agency’s analysis focuses on the timing of the geocentric conjunction – when the sun, Earth, and moon align.
“A geocentric conjunction occurs when the ecliptic longitude of the Moon is equal to the ecliptic longitude of the Sun, as observed from the center of the Earth,” the BMKG explained in a document published on its official website on Tuesday, February 3, 2026.
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According to the BMKG, the geocentric conjunction will take place on Tuesday, February 17, 2026, at 7:01 PM local time (WIB). At that moment, the ecliptic longitude of both the sun and moon will be precisely 328.83 degrees.
Because the conjunction occurs after sunset on February 17, 2026, astronomical observations to sight the hilal to determine the start of Ramadan 1447 H will be conducted after sunset on February 18, 2026, for those who rely on visual sightings. Those who use calculations (hisab) will need to consider specific criteria at sunset on February 18, 2026, the BMKG stated.
The BMKG also outlined predictions for the hilal’s altitude on February 17 and 18, 2026. Based on the agency’s maps, the hilal’s altitude across Indonesia at sunset on February 17, 2026, will range from -2.41° in Jayapura, Papua, to -0.93° in Tua Pejat, West Sumatra.
“The hilal’s altitude across Indonesia at sunset on February 18, 2026, will range from 7.62° in Merauke, Papua, to 10.03° in Sabang, Aceh,” the BMKG reported.
The agency also provided maps illustrating the geocentric elongation at sunset on February 17 and 18, 2026. Elongation refers to the angular distance between the center of the Moon’s disk and the center of the Sun’s disk as observed from Earth.
“The geocentric elongation across Indonesia at sunset on February 17, 2026, will range from 0.94° in Banda Aceh, Aceh, to 1.89° in Jayapura, Papua. The geocentric elongation across Indonesia at sunset on February 18, 2026, will range from 10.7° in Jayapura, Papua, to 12.21° in Banda Aceh, Aceh,” according to the BMKG.
The BMKG further detailed a map of the Moon’s age, defined as the time difference between sunset and the conjunction.
“The Moon’s age across Indonesia at sunset on February 17, 2026, will range from -3.07 hours in Jayapura, Papua, to -0.16 hours in Banda Aceh, Aceh. The Moon’s age across Indonesia at sunset on February 18, 2026, will range from 20.92 hours in Jayapura, Papua, to 23.84 hours in Banda Aceh, Aceh,” the BMKG stated.
The BMKG also noted that no other astronomical objects will be within 10° of the Moon on February 17, 2026. Similarly, from sunset to moonset on February 18, 2026, no other astronomical objects will be closer than 10° to the Moon.
Determining the Start of Ramadan
The start of Ramadan in Indonesia is determined through a sidang isbat, or meeting, held by the Ministry of Religious Affairs. The ministry has scheduled the sidang isbat for February 17, 2026.
Director General of Islamic Affairs at the Ministry of Religious Affairs, Abu Rokhmad, stated that the government uses an integrated approach combining hisab (calculations) and rukyatulhilal (visual sightings) to determine the start of the Hijri calendar months. He added that this approach allows the government to accommodate the diverse methods used by various Islamic organizations.
The sidang isbat will include broad representation from the Muslim community, including organizations such as NU, Muhammadiyah, PERSIS, Al-Irsyad Al-Islamiyyah, Hidayatullah, and the Indonesian Islamic Union (PUI), as well as experts in falak (Islamic astronomy) and astronomy from institutions like the BMKG, BRIN, Planetarium, and astronomical observatories.
With the sidang isbat scheduled for February 17, 2026, the beginning of Ramadan 1447 H is predicted to fall on February 18, 2026, if the hilal is sighted and meets the established criteria. If the hilal is not sighted, the start of Ramadan 1447 H will likely be set for February 19, 2026.
Indonesia utilizes standards and criteria agreed upon by the ministers of religious affairs from Brunei Darussalam, Indonesia, Malaysia, Singapore (MABIMS) in determining the hilal. According to the Ministry of Religious Affairs website, the new MABIMS criteria stipulate that imkanur rukyat – the possibility of sighting the hilal – is considered valid if the hilal reaches an altitude of 3 degrees with an elongation angle of 6.4 degrees.
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