The start of Ramadan fluctuates each year because the Islamic calendar follows the phases of the moon. A moon-sighting committee in Saudi Arabia is in charge of determining when the holy month begins: the first day of the month to the day after the sighting of the new moon. In Catalonia, from 5:37 a.m. on Monday, observant Muslims fast until the sun sets at 6:53 p.m. It will end on April 9.