The UAE's Moon sighting committee has announced that Monday will be the first day of fasting for Ramadan.
The committee convened on Sunday evening at Abu Dhabi Judicial Department and spotted the crescent moon, which marks the beginning of a new month.
The International Astronomical Centre set up telescopes on Jebel Hafeet in Al Ain, one of the country's highest mountains.
They first spot the new moon using a telescope before confirming it with the naked eye.
President Sheikh Khalifa sent cables of congratulations to the leaders of Arab and Islamic countries around the world.
Sheikh Mohamed bin Zayed, Crown Prince of Abu Dhabi and Deputy Supreme Commander of the Armed Forces, tweeted to congratulate the country's rulers on the event of the holy month and said that he prays for the safety of the Armed Forces.
The Crown Prince of Dubai, Sheikh Hamdan bin Mohammed, tweeted a video animation to mark the start of the festive period.
Ramadan is the ninth month in the Islamic, or Hijri calendar, and the holy month for Muslims, who believe it is when the Quran was revealed to the Prophet Mohammed.
Several countries have also announced the holy month will begin on May 6, including Saudi Arabia, Australia and Turkey.
The Islamic calendar is determined by moon phases, which are either 29 or 30 days long, with the appearance of a new moon signaling the beginning of a month. Searching for the new crescent can be a little tricky, however, because it is usually faint and is only visible for about 20 minutes.
Traditionally, the UAE, Bahrain and Saudi Arabia observe the holy month on the same dates, while Oman’s religious authority calls Ramadan independently of the rest of the Arabian Gulf.
Saudi Arabia leads the way in calling the start and end of the holy month, but each country has its own committee to confirm the new moon.
During this month, Muslims do not consume any food or drinks between fajr (dawn) and maghrib (sunset) prayers – not even water.
Non-Muslims should behave respectfully, remembering to dress conservatively and to not eat, drink or smoke in public during daylight hours.
Some restaurants will be closed during the holy month and almost all shops will be closed an hour before and a couple of hours after sunset. After iftar, the sunset meal when Muslims break their fast, almost everywhere will be open.
Malls are open during the day and closing times may be as late as midnight or 1am. Some bars and nightclubs may close for the month, while some have licences allowing them to stay open.
The Moon sighting committee will reconvene on the 29th day of Ramadan to search for a glimpse of the new crescent moon, which will signal the start of Eid Al Fitr. When spotted, the following morning will be announced as the first day of the 10th month, known as Shawwal.
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