Muslim authorities in Saudi Arabia and several other Middle Eastern countries say this year’s fasting month of Ramadan will begin Thursday based on the expected sighting of the crescent moon.

Clerics across the region said the moon was not visible Tuesday night, meaning it will almost certainly appear the following evening, heralding the start of the monthlong observance.

During Ramadan, Muslims refrain from eating, drinking, smoking, and sexual intercourse from sunrise until sunset. Even a tiny sip of water or a puff of smoke is enough to invalidate the fast. At night, family and friends gather and feast in a festive atmosphere.

The fasting is aimed at bringing the faithful closer to God and reminding them of the suffering of the poor. Muslims are expected to strictly observe daily prayers and engage in heightened religious contemplation. They are also urged to refrain from gossip, fighting or cursing during the holy month.

Fasting is one of the five pillars of Islam and is required for all healthy Muslims. But there are exemptions for those who are ill, and for women who are pregnant or breastfeeding. Small children are not expected to fast.

Islam follows a lunar calendar, so Ramadan begins around a week and a half earlier each year. At the end of Ramadan, Muslims celebrate the joyous Eid al-Fitr holiday, when children often receive new clothes and gifts.