Muslims around the world are marking the start of the holy month of Ramadan, a time marked by intense prayer, dawn-to-dusk fasting and nightly feasts. Muslims follow a lunar calendar and use the sighting of the new moon to determine the start of the month, which can lead to countries declaring the start of Ramadan a day or two apart. Traditionally, countries announce if their moon-sighting council spots the Ramadan crescent the evening before fasting begins.

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An official looks through a telescope for the sighting of the crescent moon to start of the Muslim fasting month of Ramadan at a religious boarding school in Jakarta, IndonesiaAntara Foto/Rivan Awal Lingga/Reuters
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The new crescent moon of Ramadan rises over the Faisal Mosque in Islamabad, PakistanFarooq Naeem/AFP

Each day for the month of Ramadan, Muslims abstain from eating and drinking from sunrise to sunset. Even a sip of water, coffee or a cigarette can invalidate one's fast. There are exceptions to fasting for children, the elderly, the sick, women who are pregnant, nursing or menstruating, and people travelling.

Many break their fast as the Prophet Muhammad did around 1,400 years ago, with a sip of water and some dates at sunset followed by prayer. It is common for Muslims to break their fast with family and friends and charities organise free meals for the public at mosques and other public spaces. The fast is intended to bring the faithful closer to God and to remind them of the suffering of those less fortunate.

Giving to charity is an important part of the holy month of Ramadan. There are two types of charity known as Zakat (a fixed amount of savings donated to the poor, mandatory as one of the pillars of Islam) and Sadaqa (voluntarily giving above and beyond the mandatory amount).

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Muslims arrive to offer the first Tarawee (special night prayer) at Mecca Masjid in Hyderabad, IndiaNoah Seelam/AFP
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A Muslim man offers the evening prayer on the second day of Ramadan at a mosque in Kolkata, IndiaRupak De Chowdhuri/Reuters
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Indian Muslims wait to break their fast at the Jama Masjid in the old quarters of New DelhiDominique Faget/AFP
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A Muslim man performs ablution before offering the evening prayer on the second day of Ramadan at a mosque in Kolkata, IndiaRupak De Chowdhuri/Reuters
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An Indian Muslim child prepares Iftar – food to break the fast – outside a mosque in Allahabad on the first day of RamadanSanjay Kanojia/AFP
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A boy learns to read the Quran at a mosque in Islamabad, Pakistan, during the holy month of RamadanFaisal Mahmood/Reuters
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Pakistani Muslim women pray before breaking their fast on the first day of the holy month of Ramadan in LahoreArif Ali/AFP
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A boy sits with others as they wait to break their fast at a charity food distribution point in Karachi, PakistanAkhtar Soomro/Reuters
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Women break their fast in a park in Lahore, Pakistan, during the Muslim holy month of RamadanMohsin Raza/Reuters
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Commuters travel past Iftar, plates of food for passersby to break their fast, in Karachi, PakistanAkhtar Soomro/Reuters
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People pray on the first day of the fasting month of Ramadan in the Ottoman-era Sultanahmet Mosque, also known as the Blue Mosque, in Istanbul, TurkeySuhaib Salem/Reuters
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Turkish soldiers fire a cannon to mark the end of the day's fasting period at the Blue Mosque Square in IstanbulOzan Kose/AFP
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People pray as they break their fast at Sultanahmet Square on the first day of the holy fasting month of Ramadan in IstanbulSuhaib Salem/Reuters
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People break their fast at Sultanahmet Square on the first day of the holy fasting month of Ramadan in Istanbul, TurkeyMurad Sezer/Reuters
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People pose for selfie as they break their fast on Istiklal Avenue, the main shopping and pedestrian street in IstanbulHuseyin Aldemir/Reuters
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Women look at their mobile phones after breaking fast at the Blue Mosque Square in Istanbul, during the first day of the holy month of RamadanOzan Kose/AFP
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An Afghan man reads the Koran at a mosque on the first day of the holy month of Ramadan in Kabul, AfghanistanMohammad Ismail/Reuters
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An boy reads the Quran in a madrasa during the Muslim holy month of Ramadan in Kabul, AfghanistanOmar Sobhani/Reuters
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Afghan boys read the Quran in a madrasa, or religious school, in Kabul during the Muslim holy month of RamadanOmar Sobhani/Reuters
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A Saudi cleric recites from the Quran, Islam's holy book, at a mosque in the town of Qatif, 400kms east of Riyadh, on the first day of the holy fasting month of RamadanHussain Radwan/AFP
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A man reads the Quran in a mosque in Riyadh, Saudi Arabia, during the fasting month of RamadanFaisal Al Nasser/Reuters
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People shop for fruits at a market on the first day of the holy month of Ramadan in Kuwait CityYasser Al-Zayyat/AFP
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Muslims break their fast with iftar during the holy month of Ramadan in Dubai, United Arab EmiratesFrancois Nel/Getty Images
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Palestinian girls pose for a picture with a Ramadan lantern in front of the Dome of the Rock at the Al-Aqsa Mosque compound in the Old City of JerusalemAhmad Gharabli/AFP
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A Palestinian man reads the Quran in al-Aqsa Mosque, on the compound known to Muslims as al-Haram al-Sharif, in Jerusalem's Old CityAmmar Awad/Reuters
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A Palestinian man reads the Quran in al-Aqsa Mosque, on the compound known to Muslims as al-Haram al-Sharif and to Jews as Temple Mount, in Jerusalem's Old City during the holy month of RamadanAmmar Awad/Reuters
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A man decorates the Qahwetna Cafe in Gaza City one day ahead of RamadanMohammed Abed/AFP
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Shia Muslim men read the Quran at the Imam Hussein shrine in the city of Kerbala, Iraq during the Muslim holy fasting month of RamadanReuters
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A child runs outside a tent after sunset on the first fasting day of the Muslim holy month of Ramadan, at al-Khazir camp for the internally displaced, located between Arbil and Mosul, IraqKarim Sahib/AFP
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Children queue up for water rations to drink at the end of the first fasting day of the Muslim holy month of Ramadan, at al-Khazir camp for the internally displaced, located between Arbil and Mosul in IraqKarim Sahib/AFP
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A family breaks their fast at al-Khazir camp for the internally displaced, located between Arbil and Mosul in IraqKarim Sahib/AFP
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A Syrian man reads the Quran during Ramadan in the rebel-held besieged eastern Damascus suburb of GhoutaBassam Khabieh/Reuters
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Children learn to read the Quran during the holy month of Ramadan in Sanaa, YemenKhaled Abdullah/Reuters
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A man carries a sack of flour he received from a local charity during the holy month of Ramadan in Sanaa, YemenKhaled Abdullah/Reuters
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Indonesian Muslims pray during the start of the holy month of Ramadan at the Al Akbar mosque in SurabayaJuni Kriswanto/AFP
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Muslim men break fast at Istiqlal Mosque during the holy month of Ramadan in Jakarta, IndonesiaDarren Whiteside/Reuters
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A child bows during the Taraweeh (special night prayers) to mark the start of Ramadan at a mosque in SingaporeEdgar Su/Reuters
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Muslims perform Taraweeh prayers to mark the start of Ramadan at a mosque in SingaporeEdgar Su/Reuters
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A girl plays inside the Golden Mosque in Quiapo, a district in Manila, the PhilippinesNoel Celis/AFP
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Security personnel fighting the militants from the Maute Islamist terror group attend Friday prayers inside a mosque in a cleared area inside the besieged city of Marawi, southern PhilippinesJes Aznar/Getty Images
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A Shia Muslim man enters the Husayniyyah prayer room during the month of Ramadan at the Al-Khoei Foundation in Jamaica, Queens, New YorkAmr Alfiky/Reuters
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People pray at the Grand Mosque of Paris at the start of the Muslim fasting month of RamadanBenjamin Cremel/AFP
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A man prays after breaking his fast on the first day of the holy month of Ramadan at a mosque in Abidjan, Ivory CoastSia Kambou/AFP
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Libyans select vegetables at an open-air market in the centre of the capital Tripoli, as the faithful prepare for the start of the Muslim holy fasting month of RamadanMahmud Turkia/AFP

Islam is the second-largest religion in the world with roughly 1.6 billion followers around the world –nearly a quarter of the global population. Ramadan is the ninth month of the Islamic calendar and observing it is one of the Five Pillars of Islam. It is a period of fasting, prayer and charitable giving believed to mark the first revelation of the Quran to the prophet Muhammad.