New Radio Telescopes

Abstract

In last 30 years radio telescopes have given astronomers an entirely new picture of universe. Radio astronomy has a distinguished record of discovering things not only unknown, but unsuspected. The record stretches from original discovery in 1930's that astronomical objects gave off radio waves (SNL: 6/3/33, p. 389), to today's excitements, quasars and pulsars. Radio observation has given scientists views of parts of universe that are blocked to human sight by opaque dust clouds. It has charted motions of interstellar gas clouds and determined their chemical composition. And much radio astronomical work has been right in middle of most fundamental of sciences, cosmology, study of origin and history of universe. As their science has progressed, radio astronomers have wished to see both farther into universe and finer and finer detail. To accomplish these purposes they have built larger and larger telescopes. Until early 1960's they were supported in this endeavor by various countries, notably American, Australian, British and French Governments. Then just about everything stopped. The reasons were mainly budgetary: The largest of projected modemn radio telescopes run into tens of millions of dollars. Compared with latest in particle accelerators, which run 10 times that, price of a radio telescope is hardly astronomical, but radio astronomy has never touched public hopes and fears way nuclear and particle physics have done. Furthermore, it is fair to say that particle physicists have also been having money troubles in recent years. During years of what journal NATURE has called the hiatus in radio telescope construction. concern over future of radio astronomy has become more and more intenEe. Now at last there are signs of a new spring. A steerable radio telescope larger than any now existing is under construction in West Germany and long dormant British and American projects are showing new life. There are two ways to see finer detail, that is, to gain higher resolution of telescope images. One is to build very large single dish antennas. The other is to build an array of small ones whose signals are combined so as to simulate signal from a single antenna as large as widest extent of array. Arrays can thus be used to simuLlate single antennas larger than could ever be built, but they pay for this advantage by slow data gathering, ponderous difficulties in pointing and severe limitations on wavelengths they can receive. Single dishes are superior in pointing, tracking and switching among wavelengths, and remain focus of astronomers' ambitions. The current generation of largest f Lilly steerable single radio telescopes are all just over 200 feet in diameter: a 250-foot dish at Jodrell Bank in England, a 210-foot one at Parkes, Australia and another 210-foot one at Goldstone, Calif. A few single dishes larger than these do exist, but they are not fully steerable and their application is thus severely limited. The current crop of large radio telescopes were all completed in early 1960's. At time radio astronomers were already projecting their next steps. But nothing further was done. A projected 600-foot fully steerable dish at Sugar Grove, W. Va., on which some work had already been done, was abruptly dropped. In 1964 a board convened by U.S. National Academy of Sciences recommended a quick start on a national radio telescope of 300-foot diameter or greater. If advice had been taken when it was given, telescope 4: f? > 0