Moon sighting

Moon sighting (Arabic: رؤية الهلال) refers to the act of observing a new crescent moon and is one of the ways to determine the beginning of a lunar month in religion. On the Islamic calendar, a month begins with the sighting of the new crescent Moon. That makes astronomy a key part of Islamic events and festivals, including Ramadan and Eid al-Fitr.

Iran
The Estehlal Headquarters is the organization and command post based in Iran  which deploys groups to monitor the sky and identify the crescent of the Moon  on the first night(s) of the Lunar month, as per the Islamic tradition of Estehlal. This marks the first day of each month on the lunar calendar. Estehlal Headquarters was established by the decree of Iran's supreme leader, Seyyed Ali Khamenei, to regulate the practice of Estehlal. The Center consists of 150 groups  with 700 members.

Saudi Arabia
The Supreme Court of Saudi Arabia has requested those who observe a crescent moon approach the nearest court and provide their testimony to assist the court in determining the beginning of Ramadan.