By André Green/reporter

More than one billion Muslims will celebrate their most sacred holiday of the year on or around Thursday.

The specific date will not be known until the night before, as it depends on the actual visible sighting of the moon, but the Islamic Society of North America estimates tomorrow as the beginning day.

The ninth month of the Islamic lunar calendar marks the beginning of Ramadan, which should run Sept. 13-Oct. 12.

During Ramadan, Allah, through the angel Gabriel, revealed the Koran to the Prophet Muhammad near Mecca.

During the Holy month, Muslims fast (the third pillar of Islam) from sunrise to sunset. They must refrain from eating, drinking, evil thoughts, actions and other physical needs.

Ramadan is considered a time of atonement, worship and charitable acts as well as the purification of oneself through prayer.

Ramadan never falls on the same day in consecutive years since the Islamic lunar calendar is shorter 11-12 day than the Gregorian calendar.

After about 30 days, the sighting of the new crescent moon marks the beginning of the 10th month and the end of Ramadan.