Jakarta. The Religious Affairs Ministry said astronomical calculations indicate that Ramadan is likely to begin on Thursday. Indonesia's largest Islamic organization, Nahdlatul Ulama, has also projected that the fasting month will start the same day after concluding that the crescent moon does not meet visibility criteria.

According to the ministry’s hisab, or astronomical reckoning, the new crescent moon does not yet meet the agreed visibility criteria across the country, said Cecep Nurwendaya, a member of the ministry’s moon-sighting team, during a seminar ahead of the isbat session on Tuesday.

Based on national visibility maps, the hilal — the first visible crescent marking the start of a new Islamic month — remains below the horizon throughout Indonesia at sunset, meaning it cannot be observed.

In Jayapura, Indonesia’s easternmost major city, the crescent’s altitude is calculated at minus 2.41 degrees. In Tuapejat in the Mentawai Islands of West Sumatra, one of the westernmost observation points, it is estimated at minus 0.93 degrees.

The negative position is linked to the timing of the lunar conjunction, which is set to occur at 7:01:07 p.m. Western Indonesia Time. Because sunset across Indonesia takes place before the conjunction, the moon remains below the horizon at dusk, Cecep explained.

Indonesia applies the regional moon-visibility criteria agreed upon by MABIMS — a grouping of Brunei, Indonesia, Malaysia and Singapore. Under the standard, the crescent must be at least three degrees above the horizon at sunset and have a minimum elongation, or angular distance between the moon and the sun, of 6.4 degrees.

Although Indonesia previously used a two-degree minimum altitude, research showed that visibility at that level was highly unlikely. The threshold was later raised to three degrees to improve certainty.

The Central Board of Nahdlatul Ulama, known as PBNU, through its Falakiyah Institute, said its own calculations show the hilal height across Indonesia ranges between one and two degrees, with elongation also between one and two degrees — both below the MABIMS threshold.

Ahmad Izzuddin, an official at PBNU’s Falakiyah Institute, said that based on these figures, it is highly unlikely that anyone would successfully sight the crescent.

Based on this assessment, PBNU concluded that the month of Sha’ban will be completed at 30 days, making Wednesday (Feb. 18) the final day before Ramadan. Tarawih prayers are therefore expected to begin on Wednesday evening, with fasting starting Thursday morning.

Religious Affairs Minister Nasaruddin Umar said earlier Tuesday that the crescent’s position — around minus two degrees in much of the country — makes observation “almost impossible.” However, he stressed that the government would wait for the outcome of the isbat session before making an official announcement.

Indonesia, home to the world’s largest Muslim population, uses a hybrid system combining astronomical calculations (hisab) and physical moon observation (rukyat) to determine the start of Islamic lunar months. This year, observation is being conducted at 96 locations nationwide.

Differences in determining the start of Ramadan are not uncommon in Indonesia. Muhammadiyah, one of the country’s largest Islamic organizations, primarily relies on astronomical calculations, while Nahdlatul Ulama and other groups prioritize physical sighting supported by calculations.

Such methodological differences have occasionally led to varying start dates among Indonesian Muslims in recent years.

Nasaruddin urged the public to remain united regardless of the decision. “Indonesia has experience managing differences in determining the first day of Ramadan. We remain united amid diversity,” he said.

Historically, the isbat session has served as the government’s official national reference for the start of Ramadan and Eid al-Fitr. The ministry said it continues to position itself as a bridge among Islamic organizations in determining key religious dates.