Arecibo Observatory, Arecibo, Puerto Rico
The Biggest Dish
The radio telescope at Arecibo Observatory in Puerto Rico looks like the set for a James Bond film—the 305-meter dish set into the hilly countryside near the town of Arecibo is the largest and most sensitive radio telescope ever built. Surrounded by lush vegetation and set into an ancient sinkhole, it has been listening to radio signals from the stars since 1963, with an 810-tonne platform suspended above the dish to receive signals bouncing from its surface.
The surface of the dish is made of 40,000 perforated aluminum sheets formed into a spherical shape. Since the dish itself cannot move, the receivers suspended above it can shift to listen to different parts of the sky. Hanging from the platform is a dome-like structure that can be moved so that it can focus on signals received from particular areas of the sky. Since the dish is spherical, not parabolic, its shape can be used to study different parts of the sky without moving the dish itself (see also Chapter 67 on the Sound Mirrors, which used a similar technique).
And the Arecibo Observatory can do more than just listen—the dome incorporates a 1-megawatt radar that can be used to bounce a signal off a spacecraft or planet ...