The month long Islamic holiday of Ramadan began Monday morning in much of Asia with the first sighting of the new moon. Muslims in the Middle East began the festival/fast on Sunday because the new moon was visible there a day earlier. Ramadan is a religious observance; Muslims fast to mark what they believe is the anniversary of God's revelation of the Koran to Mohammad. The Associated Press describes the emotional nature of the holiday: militant groups see the holiday as an occasion for promoting their causes, while many mainstream Islamic organizations use Ramadan to promote non-violence and religious introspection. The holiday can be hard on tourists in Muslim areas. Muslims do not eat or drink during daylight hours in the month of Ramadan, so many restaurants are closed.