Today is Eid al-Fitr, the Muslim holiday that marks the end of Ramadan, the holy month of fasting. Except that it isn't.
Today, many Muslims in the United States, Egypt, Saudi Arabia, and Jordan are celebrating Eid. Meanwhile, many Muslims in Indonesia, South Africa, India and Oman are not celebrating Eid until Wednesday.
Saad al-Khathlan, professor of jurisprudence at Imam Mohammed bin Saud Islamic University in Saudi Arabia, told al-Anbaa newspaper that disagreements over deciding the first day of Ramadan or Eid have existed since the first days of Islam.
"For the past fourteen centuries, Muslims have never agreed to celebrate Eid on the same day," he said.
Since the Islamic calendar is lunar, rather than solar, each month begins when the moon is sighted. Moon-sighting, however, depends on different factors such as geographical location and weather conditions — it's difficult to see the moon when the sky is cloudy. Also, some Muslim scholars say it is permissible to use telescopes for moon-sighting while others insist that only the naked eye can be used to do this. Moreover, some scholars recognize astronomical calculations as an acceptable method for determining the beginning of months.
All these differences lead to different conclusions when Islamic authorities in many countries around the world decide on which day Eid would fall.
Usually, the top religious authority in each country, which is typically part of the government, would make the decision on what day Eid is. But even when these authorities decide, not everyone in that country would abide by it as minorities don't necessarily agree with the official religious establishment in said country. For example, the Bahraini government announced that Eid is Tuesday. But Shia in Bahrain, who make up around 70 percent of population in this country, will celebrate Eid on Wednesday.
Some Muslims say they wish that, in the spirit of unity, everyone would celebrate Eid on the same day. But not everyone agrees.
Dr. Ali Gomaa, the Grand Mufti of Egypt, told Laha magazine that this should not be a point of contention. "There is no reason whatsoever for this issue to be a source of disagreement and conflict among Muslims," he said.
Egyptian blogger Raouf Shabayek agrees with Gomaa. "You see some comments like 'look at how backward Muslims are, they can't even agree on what day their Eid is'," he wrote on his blog. He says this is the wrong approach to look at the issue because we need to accept variations and embrace diversity.
"When we learn to accept that, it won't hurt you if Egypt celebrated Eid before Saudi Arabia," he wrote. "Because this is the nature of Islam, humans and the universe."
Ahmed Al Omran is an intern with NPR's social media desk. He's blogged from Saudi Arabia since 2004, until he came stateside to attend Columbia University's Graduate School of Journalism.