Kari Ansari recalls getting ready to celebrate one of the most important religious holidays of the year — the end of the monthlong Ramadan fast.

She and her husband bought new clothes and gifts for their three children and planned a special family meal. But there was one obstacle to starting the celebration: Leaders of the two local mosques couldn't agree when the feast, called Eid al-Fitr, should begin.

"We would just be sitting up at night waiting to hear the decision," said Ansari, who lives in Herndon, Va., and is editor of America's Muslim Family magazine.

The Muslim practice of following a strict lunar calendar, requiring a naked-eye sighting of the new moon to start a holiday the next morning, has divided the Muslim community on its most sacred days. Now a scholarly panel that advises American Muslims on religious law is trying to end the confusion.

The Fiqh Council of North America announced last week that it would no longer rely on moon sightings to determine the start of holidays and would instead use astronomical calculations. The panel released an Islamic calendar that runs through 2011, hoping Muslims in the United States and Canada can be persuaded to trade the old way for the new.

The schedule problem is more than a minor inconvenience. School calendars and vacation time from work, for instance, depend on knowing dates in advance.

"There will be a lot of resentment at first," said Khalid Shaukat, an astronomer and research physicist with the U.S. Nuclear Regulatory Commission, who calculated the calendar for the Fiqh Council. "But I expect that as the time goes on and we educate them, people will see the benefit of this and understand that what may seem like a new approach to them is not against Islamic jurisprudence."

The date of the Eid is based on the Hadith, traditions taken from the life of the Prophet Muhammad. The prophet taught that the holiday marking the end of Ramadan comes the morning after a nighttime sighting of the new moon.

Under the most conservative interpretation, two credible witnesses with expertise in Islamic sharia law have to see the crescent moon with the naked eye before their observations can be accepted, said Sulayman Nyang, an expert on Islam at Howard University.

But the Fiqh Council contends that the prophet used direct sightings only because no other method was reliable in his lifetime. "Now, we know scientifically whether the moon is there, even if it is not sightable because of the weather conditions," said Muzammil Siddiqi, the council chairman.