Muslims worldwide begin a month-long period of fasting, prayer and introspection Saturday with the appearance of the crescent moon.

Ramadan, the holiest month of the year for Muslims, begins Saturday as believers worldwide mark it with fasting and praying.

Muslims believe Allah revealed the first texts of the Koran to the prophet Mohammed during the month of Ramadan. They look to the month as a time for spiritual purification and prayer.

The holy month begins with the first sighting of the new crescent moon – which is due this year on Sept. 23. All Muslims older than 12 are expected to fast from sunrise to sunset, forgoing any food or drink until nighttime.

Their fasting continues every day for the next 30 days, and the next new crescent moon rises, marking the festival of Eid al-Fitr. That festival falls on Oct. 24 this year. Muslims adorn their homes with lights and decorations for the festival, celebrate with their friends and family and give treats to their children.