So, the holy month of Ramadan is coming to a close, and Muslims all over the world are preparing their Eid al-Fitr celebration parties.
But hold up! Before you start making your Eid feasts, there's just one, kinda small problem.....
It’s all down to disagreements on whether the new moon – which marks the end of the fasting period – has been sighted.
Ramadan officially ends when the new moon is sighted, after which Eid is formally announced.
The sighting is usually carried out by various committees in countries where Islam is the national religion – usually in Saudi Arabia, Kuwait, and the UAE. However, separate sightings have been known to take place in other countries too, including Iran, Iraq and Bangladesh.
The number of sightings means that Muslims from different sects, denominations, and even countries can celebrate Eid at different times, depending on when their imams confirm seeing the new moon.
On Thursday, the High Judiciary Council of Saudi Arabia announced the start of Eid, after claiming it had seen the moon.
The council made the announcement after Saudi Arabia and observatory councils in Kuwait and the UAE confirmed they had also seen the moon in their countries.
It means that Muslims across the world who follow guidance from Saudi Arabia, including from the US, the UK, and the rest of Europe, will celebrate Eid on Friday.
However, others have disputed the observation, saying Muslims should only celebrate once they see the moon in their own countries.
Meanwhile, Muslims from other denominations, such as the Shiites, believe that Eid can only start when it is announced that a "Marja", or a scholar with authority, has observed the moon. Often, the Marja will be based in Iran.
As a result, some Shiite mosques in the UK will celebrate Eid on Saturday or Sunday, rather than Friday.
The disputes over moon observations happen regularly, according to Qari Asim, imam of the Makkah Masjid in Leeds.
"The prophetic saying is 'break your fast once you've sighted the moon', but the issue is, how do you sight it? With the naked eye or with an aid?" Asim told BuzzFeed News.
There are various theories among Muslim scholars over how Eid should be announced, Asim said.
"In European countries, Muslims can't see the birth of the new moon, so they often trust the judgment of official observatory committees in Muslim majority countries," Asim said.
"But other Muslims will also celebrate Eid in line with the nearest Muslim majority country, such as Morocco, although there can be big delays with this.
"The problem with following Saudi Arabia is that many believe that they are not calling Eid when they see the new moon, but when the new moon is born. The moon needs to be 18-20 hours old to be visible, so that means there will always be a delay between when the new moon is born and when you're actually able to see it.
"So there are Muslims that believe Saudi Arabia is calling Eid earlier than they should be."