A panoramic view of the ground screen surrounding the main antenna dish of the Arecibo Observatory in Puerto Rico. The ground screen is designed to screen out terrestrial radio interference that would otherwise disrupt the operation of the radio telescope. The radio telescope's main feed can be seen suspended above the antenna. Apart from being the world's largest radio telescope for many years (305m in diameter), Arecibo is also known for its use in the search for extraterrestrial intelligence (SETI).