Upgraded Arecibo radio observatory. Aerial fisheye lens view of the Arecibo radio telescope, with its gregorian subreflector system newly installed in 1997. This largest radio telescope in the world is situated in a natural crater in the mountains of Puerto Rico. The new subreflector system with two mirrors is housed in a 90-tonne dome receiver seen suspended 130 metres above the fixed dish. It can send and receive signals to examine planets and asteroids & also analyse Earth's upper atmosphere. To scan the sky the dome is steered above the 305m dish. The upgrade includes a 16m high buffer screen around the dish and a new radar transmitter that increases Arecibo's power by 20 times.