As most of the Arab and Muslim world prepares to celebrate Eid Al Adha on Wednesday, four countries, India, Bangladesh, Brunei and South Africa, have announced that they will mark the holiday a day later, on Thursday, following differing moon-sighting determinations for the start of Dhul Hijjah.Official religious authorities in the four countries said the first day of Dhul Hijjah for 2026 began on Tuesday, May 19, placing the Day of Arafat on Wednesday, May 27, and Eid Al Adha on Thursday, May 28.The variation stems from the longstanding differences among Islamic countries in determining the start of lunar months, with each nation relying on its own moon-sighting procedures, astronomical calculations and geographical visibility conditions. As a result, the dates of major Islamic occasions can differ by one day between countries.In contrast, the International Astronomical Center said that more than 28 Arab and Islamic countries, along with Muslim communities in several Western nations, aligned their moon sighting with Saudi Arabia, where Eid Al Adha will be observed on Wednesday, May 27.Those countries include the UAE, Egypt, Jordan, Kuwait, Qatar, Turkey, Pakistan and Malaysia, in addition to Muslim communities in the United Kingdom and the United States.Astronomers say such differences are common and recur annually due to varying geographical and astronomical conditions, as well as differences between countries that rely primarily on naked-eye sightings and those that incorporate astronomical calculations into the moon-sighting process.