Ramadan crescent moon: how it is spotted and why it matters

The start of Ramadan is set by sighting the first crescent moon, a practice that mixes naked-eye observation, instruments and astronomical calculations. The UK will host a nationwide moon-sighting event at the Royal Observatory on the evening of Wednesday, February 18.

Muslim communities are preparing to begin Ramadan, which starts when the first crescent moon is sighted after sunset. The crescent determines the start of the ninth month of the Islamic lunar calendar and the timing of Eid al-Fitr. Sighting is a long-standing practice known as Ru'yat Al Hilal and remains meaningful across different communities. Scientific methods and public announcements now sit alongside traditional observations. Key facts: - The crescent moon has been reported sighted in Saudi Arabia. - Observers look for the faint crescent in the western sky shortly after sunset on the 29th day of the lunar month; if it is seen the new month begins the next day, and if not the month is completed as 30 days. - The astronomical new moon occurs when the moon is between Earth and the Sun and cannot be seen; the visible crescent can appear hours later above the horizon. - Sighting is traditionally done with the naked eye, though telescopes and binoculars are increasingly used and astronomical calculations inform many decisions. - Regional differences mean Ramadan may start on different days in different countries; the UK typically follows an announcement from Morocco. - The Royal Observatory and the New Crescent Society are hosting a nationwide moon sighting event on the evening of Wednesday, February 18, with Imad Ahmed and Royal Observatory astronomer Jake Foster presenting from Greenwich. Summary: Moon sighting remains both a religious ritual and a moment where tradition and astronomy meet, influencing when communities begin Ramadan. Some countries have reported sightings while others will wait for local or national announcements. The UK has a scheduled public event at the Royal Observatory on February 18 to observe and discuss the crescent sighting.