Word: dishes
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Word flashed to all the worlds space centers that Mariner II was in trouble. But all was not lost; at Goldstone the scientists pointed their great dish antenna with special precision and sent a radio command to Mariner II, 36 million miles away. The radio waves, traveling with the speed of light, took more than three minutes to get to their target. At last came the voice of Mariner II, reporting that it had heard the command and turned on its instruments...
Instead of taking quick pictures of large parts of the sky, radio telescopes must scan slowly, gathering details one by one. As a radio telescope's beam (its field of sensitivity) moves across the sky, the radio waves collected by the dish are focused on an antenna and detected as an extremely feeble electrical current. This current is amplified by intricate electronic apparatus until it is strong enough to move a finely balanced pen and draw a wiggly line on a strip of paper. Small wiggles mean little or nothing, but a good-sized bulge means that some object...
...Dishes & Holes. Parabolic dishes make by far the most versatile radio telescopes; they can be used to tune in on several wave lengths at the same time. The most famous dish, the 250-foot monster at Jodrell Bank, near Manchester. England, started work in 1957 and is still going strong. Probably the most effective dish is the 210-footer at Parkes, Australia. The biggest dish. 300 ft. in diameter, is at Green Bank...
...steerable dishes that can be turned to point all over the sky are extremely expensive. For large area and proportionately high sensitivity at reasonable cost, radio astronomers dig cylindrical or hemispherical holes in the ground and line them with radio-reflecting metal. These immovable reflectors cannot be steered except by electronic trickery, but their sheer size gives them enormous power. The cylindrical telescope at the University of Illinois has 3½ times the area of the Green Bank dish...
...important type of radio telescope does not try to observe celestial objects with a single antenna. Instead, two antennas are placed a considerable distance apart and connected electronically so that they function like parts of a single, very large dish. Since a telescope's resolution is proportionate to its width, the double antenna has a far narrower beam than a single dish. Even finer resolution is obtained by long, rocking metal troughs that gather radio waves and focus them so that they interact with waves gathered by another antenna running at right angles to the first. In Australia...