Eid ul-Adha, one of two major Muslims holidays, will be celebrated on either Saturday, October 4, 2014, or less likely, on Sunday, October 5, 2014. October 4 is the expected date based on astronomical calculations. (More on this issue below).
What is Eid ul-Adha? Eid means "holiday" or "festival" and ""ul-Adha" means "the sacrifice". This "Holiday of the Sacrifice" commemorates Prophet Abraham's willingness to obey the command of God when he was called on to sacrifice his much beloved son. Like Christians and Jews, Muslims believe that God did not allow Abraham to carry out such a task, but was meant to show Abraham's complete devotion to his Creator.
The date of Eid ul-Adha coincides with the end of the annual Muslim pilgrimage to the City of Makka. The pilgrimage or "Hajj" is a rite that every Muslim will try to complete in one's lifetime if one can afford it. The millions of Muslims who participate in the annual pilgrimage will all celebrate the Eid together. In a sign of unity, Muslims around the world will try to celebrate the Eid on the same day as those who are in the City of Makka.
So, why don't we not know the exact date on which the holiday will be observed? The answer is easy, but it takes a little bit of explanation.
For all their religious observances, Muslims follow a Lunar Calendar. A lunar month is either 29 or 30 days. Historically, throughout the Muslim world, the beginning of a new month was determined by visually sighting the crescent of a "newly born" (waxing) moon. Despite this historical tradition, many Muslims, including the Islamic Society of Milwaukee, have adopted a more accurate and scientific approach, which is to rely on scientific astronomical calculations on which the exact date and time of the moon's birth can be determined. Based on the "calculation" method, Eid ul-Adha will be on October 4th this year.
In the the City of Makka, which is the site where Muslims make their annual pilgrimage, the authorities follow the visual sighting method and not the calculation method. Based on astronomical data, it is highly likely that the new crescent moon will be visually observed in Makka on the same night as determined by calculations. However, there is a possibility that the crescent moon may not be visually observable, which would therefore push the date back by one day!
Although the Islamic Society of Miwaukee is expecting the celebration to be on October 4, in order to have a unified international celebration, they will defer to the decision of the Hajj (Pilgrimage) authorities and celebrate the holiday on the same day as those on Hajj celebrate the holiday, which will likely be October 4, but can be October 5.
One final item: the holiday of Eid ul-Adha falls on the tenth day of the new month. The first day of the month (when the crescent is expected to be sighted) is September 25. Therefore, Muslims will know the exact day of this holiday a little more than a week before it is to be celebrated.