Ramadan most likely begins on Thursday, pending the sighting of the moon Wednesday evening, as the world's one billion Muslims embark on their annual month of fasting and spiritual renewal. Ramadan, the ninth month of the Islamic (lunar) calendar, is cherished as the month in which the first verses of the Qur'an were revealed to the Prophet Muhammad (peace be upon him). During the fast, Muslims abstain from food, drink and sexual intercourse during the daylight hours.