The UAE's moon-sighting committee will look to the skies to decide the start date of Eid Al Fitr on Tuesday evening.
They will meet after maghrib prayers to attempt to sight the new crescent moon which would herald the start of the month of Shawwal, which has the Eid festival at its beginning.
If the new moon is visible, the holiday will begin on Wednesday.
If not, it will start the following day.
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Astronomers previously forecast that Ramadan will likely consist of 30 days in the UAE, therefore Eid Al Fitr is expected to fall on Thursday.
“The moon does not circulate or orbit the Earth at the same time every month, sometimes the orbit is longer and sometimes shorter. There is usually a difference of about six hours each month,” said Dr Hasan Al Hariri, chief executive of the Dubai Astronomy Group.
“The length of the lunar calendar is 29 days, plus some additional hours, which means the month can last 29 or 30 days, depending on the orbit.
“With that element in play, we have to understand that this is how we determine the right position of the crescent to announce a new month.
“Looking at the crescent, it should be high in the sky and bright, not dim.”
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Dr Hariri said on Tuesday the moon would set before the sun by 11 minutes, so there will not be a clear sighting of the moon.
Unlike the Gregorian calendar, which is solar, the Islamic calendar is lunar, meaning the date for Ramadan and Eid Al Fitr change each year. Typically, an Islamic month is 29 to 30 days long, but not 31 days.
What is Eid Al Fitr?
Eid Al Fitr marks the end of the month-long fasting period.
Noted as a festive holiday, people across the Arab world and Muslim nations often celebrate the occasion with family and friends, sharing food, gifts and prayers and offering charity to those in need.
It is the first of two Eids of the Islamic calendar, with Eid Al Adha observed later in the year.
This year, with Covid-19 restrictions in place, well-wishers in the UAE have been urged to celebrate at home with immediate family to help stem the spread of infection.