MUHAMMADIYAH.OR.ID, YOGYAKARTA – In Islamic astronomy, Muslims use two approaches, ru’yah (lunar sightings) and hisab (mathematical and astronomical calculations), to determine lunar hijri.
The ru’yah method began when Rasulullah said, “Observe fast when you see it (the new moon) …” However, due to the development era, astronomy enables us to calculate the position of the moon and the sun so that we can determine the beginning of the months in next coming years.
Those two methods often lead to debate, particularly the arrival of Ramadan, Eid al-Fitr, and Eid al-Adha. Thus, a notion of the global Islamic calendar is necessary.
According to a Muhammadiyah Falak expert Susiknan Azhari, there are two Islamic calendar arrangements, the Urfi calendar and and hakiki calendar. The urfi calendar is based on the average of the orbit of the moon to the earth. Meanwhile, the hakiki calendar is based on the position of the moon (hilal) toward the horizon.
The lunar hijr making uses a method of wujudul hilal. Susiknan explained that the the new moon begins when (1) ijtima’ (conjunction) occurs, (2) the sun sets and the moon hasn’t set yet, (3) the first visible crescent of the moon in the western sky after sunset.
“The three criteria are based on Yaseen verse 39-40 and other verses, hadith, fiqh concepts, and astronomy. To determine the new moon must meet the criteria. If we cannot observe one of the criteria, it means that the new moon doesn’t happen yet,” stated Susiknan on Thursday (1/4).