Calculations by astronomers say Ramadan's new moon will be born on May 4 at 22:47 GMT, but it might not be visible.
On Sunday evening, however, the new moon should be visible to the naked eye, making it likely that many countries will observe the first day of fasting on May 6.
The actual visibility of the crescent will depend on factors such as atmospheric conditions, cloudiness and the distance between the sun and the moon on the horizon.
According to the Astronomy Centre, it is impossible to see the crescent moon in areas marked in red on Saturday, May 4 [Screenshot: Astronomy Centre]
The crescent is expected to be visible using optical aids in areas marked in blue. In the magenta areas, it could be seen using optical aid or by the naked eye, if atmospheric conditions allow, while the moon will be visible to the naked eye in green areas [Screenshot: Astronomy Centre]
Muslim lunar months last between 29 and 30 days, depending on the sighting of the new moon on the 29th night of each month. If the new moon is not visible, the month lasts 30 days.
To declare the beginning of Ramadan, Saudi Arabia and other Muslim-majority countries depend on the testimonies of local moon sighters. The Judicial High Court then decides when Ramadan begins.
Saudi Arabia's official Umm al-Qura calendar marks the first day of Ramadan asMay 6, 2019.