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Their task was not easy. Radio astronomy depends on electromagnetic waves, which are much harder to handle than the visible light that the human eye receives with such marvelous ease and precision. Radio waves are many thousand times longer than light waves, and because of inflexible laws of physics, this means that radio telescopes must be enormously wider than optical telescopes before they can distinguish objects equally small.
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 deep in space is sending radio waves down the telescope's beam.
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. W. Va.
Big 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.
One 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, and at Cambridge University. England, such intricate apparatus record information on punched tape and feed it into electronic computers for analysis. They have an effective beam so slender that it can distinguish objects many billion light-years distant in space. The most complex setups of all use two dishes scores of miles apart, feeding their information by microwave beams to a common center.