How do you deal with the Muslim lunar-based holidays whose timing is only known a few hours or days ahead of time?
We have recently completed a five year project designed to provide accurate predictions for the dates of Muslim lunar-based holidays. The Koran says that each Muslim month should begin upon the sighting of the new moon. In practice, each country has its own method of determining the start date of the month. This means that a given holiday is often observed on different days in different countries. Our research project looked at many years of historical observations to determine the methodology used by each country. As a result, we believe our predicted dates are now as accurate as is feasible given that many countries rely on the naked eye to determine the start of the month. Prior to the completion of the project, it was our practice to place an asterisk in the data files next to each Muslim holiday to indicate a high degree of uncertainty. That practice is no longer in effect.
