Once crescent-sighting is confirmed, an official announcement of the beginning of Ramadan will be sent.
For the followers of Sayed Sistani, Sayed Khamenei, and Sayed Khoei, the first of Ramadan will most likely fall on Thursday February 19th pending crescent-sighting. For followers of Sayed Fadlallah (ra) the first of Ramadan will fall on Wednesday February 18th.
