(MENAFN - Morocco World News) Rabat- Each year, Muslims around the world predict the first day of Ramadan using one of two acclaimed traditional methods: astronomical calculations and moon-sighting. The first appearance of the 'hilal,' or lunar crescent, determines the beginning of the month in the Hijra Islamic lunar calendar, as Prophet Muhammed (peace be upon him) said: 'Do not fast until you see it [the crescent] and do not break the fast until you see it, and if it is covered then complete the month.' Weather conditions and the distance between the sun and the moon affect the visibility of the crescent to the naked eye. Cloud cover, in addition to the proximity of the sun and moon, can obscure the crescent sighting. As a result, the first day of Ramadan and other Islamic celebrations like the Eid vary across Muslim countries. The entire Islamic world anticipates the emergence of the crescent moon in the night sky to mark the start of the Ramadan fast the following day. Some experts apply precise astronomical calculations to predict the first day of the holy month, in order to augment the direct visual sighting method. The synodic, or lunar, month takes about 29.53 days to transition from one new moon to the next. After the conjunction with the sun, the new crescent moon is visible. Many Muslim countries, like Morocco, Saudi Arabia, India, Iran, China, Oman, apply only local sighting. On the other hand, countries like Algeria, Egypt, Libya, Turkey, and Tunisia primarily rely on precise astronomical calculations for their religious predictions, including the timing of the waning moon and its precise position between the Earth and the sun. This year, according to Moroccan astronomers, the crescent will appear on the evening of Wednesday May 16; Ramadan will commence Thursday, May 17. Recently, Moroccan astronomer and researcher Abdelaziz Kharbouch Al-Ifrani told Morocco World News that all Muslim countries will fast the first day of Ramadan in unison on May 17, a rare incident. He explained that the crescent will likely remain hidden on Tuesday, May 15, the day that countries like Saudi Arabia have predicted for the moon's appearance. Regarding other important Islamic holidays, astronomer Dr. Hicham El Issaoui has predicted that Eid al-Adha will occur on Wednesday, August 22, and that the first day of the Islamic year, Fatih-Muharram, 1440, will occur on Tuesday, September 11. The birthday of Prophet Muhammad (PBUH), Mawlid al-Nabi al-Sharif, will be celebrated on Tuesday, November 20, 2018. Ramadan month can last from 29 to 30 days during which Sunni Muslims fast from sunrise to sunset, while Shiites wait to break their fast until the redness of the sun disappears from the sky. Ramadan is not only a month for Muslims fulfill one of the pillars of Islam through abstinence from food and drink: it is also a time for spiritual cleansing and reflection. As the messenger of Allah said, as narrated by Imam Al-Bukhari: 'When Ramadan enters, the gates of Paradise are opened, the gates of Hellfire are closed and the devils are"