The Big Dish at Jodrell Bank, the world’s largest fully steerable radio telescope dish for nearly twenty years, greatly advanced radio astronomy, making possible the discovery of several celestial radio-wave sources.
From prehistoric times to the 1930’s, astronomy relied almost exclusively on information obtained with the human eye, even if this visible light had been funneled by a telescope or recorded photographically. Amid New Jersey potato fields, that changed. In 1931, while searching for the source of static in ship-to-shore radio communications, Karl G. Jansky, an engineer for Bell Laboratories, built a large radio aerial in the New Jersey countryside. Eliminating all possible terrestrial sources of the radio hiss, such as thunderstorms, Jansky realized that he was detecting radio waves from space. The region above the stinger of the Scorpion in the constellation Scorpius emitted the strongest waves. This was soon recognized as the direction of the center of the Milky Way galaxy.
The Big Dish at Jodrell Bank.
Radio waves and visible light are members of a family, called electromagnetic waves, to which X rays, gamma rays, infrared waves, ultraviolet waves, and microwaves belong as well. Caused by accelerating electrons, all electromagnetic waves move with the same speed in a vacuum, but they differ in frequency, that is, in the number of oscillations of the wave per second. The frequencies of visible light range over a factor of about two; borrowing a musical term, astronomers sometimes refer to this spread as an octave.
The problem astronomers experienced with the myriad octaves of electromagnetic radiation may be compared to the life of someone in a house with fifty windows, each with a slightly different view of the surroundings. Until 1931, astronomers had been able to open only one of those windows: the window of visible light. Jansky’s detection of these radio waves, however, opened many new windows for science, inaugurating what is now known as invisible astronomy. Invisible astronomy utilizes about 50 octaves of electromagnetic waves; the twentieth century’s burgeoning of astronomical information was a direct result.
Astronomers recognized the potential of Jansky’s discovery only after Grote Reber demonstrated the value of observing the heavens at radio frequencies. Reber, an amateur astronomer, read of Jansky’s work and built a dish a little less than 10 meters in diameter in the garden of his home in Wheaton, Illinois. It was the first radio detector constructed in the shape of a paraboloid, a surface generated when a parabola is rotated about its axis. Reber’s radio dish could be pointed toward any part of the sky. Reber completed the first survey of astronomical radio sources in his spare time and reported his findings to the scientific community during World War II.
The war stimulated research into radio transmission and detection, including work by Bernard Lovell, the eventual creator of the Big Dish; many historians attribute the success of the Royal Air Force during the Battle of Britain to the invention and refinement of radar, an acronym for “radio detection and ranging.” With radar, the reflection of a broadcast radio signal allows the location of an object. The English led the field in radar and radio astronomy because of their weather. Unlike optical signals, radio waves are unaffected by clouds; therefore, locations that are often overcast may serve for radar or radio astronomy. One of the premier English investigators of radar was Lovell, who, after completing his doctorate in physics at Bristol University in 1936, became assistant lecturer in physics at the University of Manchester. Applying his technical skills for the Air Ministry Research Establishment during World War II, he led the development of one form of airborne radar.
The end of the war in Europe made available radio and radar research for both war surplus equipment and veteran experimenters, including Lovell. Returning to the faculty of the University of Manchester with two trailers of radar equipment borrowed from the army, Lovell followed up on a question that had arisen during his wartime research and demonstrated in October, 1946, that meteor showers could be studied by radar. To avoid radio interference from the city of Manchester, Lovell conducted his research at the University’s Jodrell Bank Experimental Station in Cheshire, 32 kilometers south of Manchester. At the time, Jodrell Bank was a botanical research station; no one suspected it would become a global center for a new branch of astronomical research.
Soon afterward, Lovell erected a stationary radio aerial almost 67 meters across. If all other factors, such as materials and specific design employed, are the same, then bigger is better—a fact just as true with radio telescopes as with optical telescopes. A larger telescope can detect fainter signals, a phenomenon analogous to cupping a hand behind one’s ear to hear fainter sounds. In addition, more collecting area increases resolution, that is, the ability to see details and distinguish two adjacent sources (the ability, for example, to tell whether an approaching automobile is using one headlight or two).
Although this large dish soon afforded fascinating glimpses of the radio universe, its immobility frustrated Lovell and his colleagues. Carried by the rotation of the earth, it swept across only a paltry swath of the sky. To remedy this, Lovell proposed in 1949 the idea of a radio telescope which, though comparable to the fixed dish in diameter, was fully steerable. Although its scientific impact was inestimable, difficulties in obtaining the requisite funding impeded its construction. In lobbying for the Big Dish, Lovell displayed the tenacity and persuasiveness that served him and his research projects for many years. Named in 1951 as director of the Jodrell Bank Laboratory and the first person to hold a chair in radio astronomy, Lovell convinced the Nuffield Foundation
There were many technical hindrances facing Sir H. Charles Husband
A second and greater impediment confronting Husband was the integrity of the huge reflector: It must retain its precise paraboloidal shape to within a few centimeters either when moved by the gear-and-rack mechanisms or when subjected to wind. Wind can cause a structure to flutter or undergo large vibrations until the structure shakes to pieces. In the preceding decade, a suspension bridge over the Tocoma Narrows had met a similar fate from a mild wind; high-speed aircraft had lost their wings to similar effects.
To maintain the reflector’s integrity when subjected to strong winds, engineers at the National Physical Laboratory studied scale models of the Big Dish in wind tunnels under gale conditions and then refined its design. Eventually, Husband used nearly 2 million kilograms of steel in the entire telescope, some 300,000 kilograms in the 76-meter-wide bowl itself, which is more than two and one-half times the diameter of the dome of the Grand Rotunda in the United States Capitol Building. The rigidity of the dish is even more striking when one recognizes that, if inverted, it would have formed the largest domed roof in the world at that time.
Construction of the facility was authorized in 1952. Through the ensuing four and one-half years, Husband and Lovell met many obstacles, fiscal as well as technical. The Big Dish finally cost almost $2 million, a cost overrun of about $800,000. Lovell encountered controversy often during his career; at one point during the construction of the Big Dish, Lovell was threatened with imprisonment because he was unable to give a university official a writ for a million pounds. Nevertheless, the scientific return on this sizable investment began during the evening of August 2, 1957. That night, the Milky Way wrote its radio signature on the detectors of the Big Dish for the first time.
Originally, the Big Dish had two primary scientific missions. Functioning as a giant ear, it could listen to the radio waves produced in various parts of the sky. Also, alternately transmitting a burst of radio energy and listening for the echo, it could be used for radar studies of objects within the solar system. During its long and distinguished lifetime, the Big Dish would hear many signals of great scientific interest. Few, if any, however, would create the public sensation occasioned by Lovell’s announcement to the press on October 13, 1957, that he had tracked successfully the carrier rocket of Sputnik 1, the first artificial satellite, as it had flown over England the previous night.
Two years later, on September 13, 1959, Lovell verified that Luna 2, the first spacecraft to reach the lunar surface, had crashed on the Moon. He also tracked the first lunar orbital mission by Luna 10 in 1966 and the epochal human landing on the Moon by Apollo 11 on July 20, 1969. Although this score-keeping in the space race accounted for less than 2 percent of the total research at Jodrell Bank (now more properly called the Nuffield Radio Astronomy Laboratories), Lovell received much publicity.
Led by the Big Dish, the radio telescopes at Jodrell Bank scored many scientific breakthroughs, among them measuring the angular diameter of radio sources and detecting radio waves from nebulas completely outside the Milky Way. These nebulas—cool clouds of gas and dust—contain atoms of neutral hydrogen in their lowest energy states that emit a distinctive radio signal 21 centimeters in wavelength, which is the distance between crests of the wave. One expensive modification to the Big Dish during its construction enabled it to detect radio waves of that 21-centimeter wavelength.
The Big Dish is not the only instrument that Lovell contributed to astronomy; the Multi-Element Radio-Linked Interferometer
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Agar, John. Science and Spectacle: The Work of Jodrell Bank in Post-war British Culture. Amsterdam: Harwood Academic, 1998. Uses the Jodrell Bank telescope as a case study to discuss the relationship of science to postwar British culture generally. Includes discussions of the telescope’s effects on the environment, its struggle for funding, and the role of spectacle in the popular understanding of both astronomy and science as such. -
Cornell, James, and John Carr, eds. Infinite Vistas: New Tools for Astronomy. New York: Charles Scribner’s Sons, 1985. A compilation of eleven essays, published under the auspices of the Smithsonian Institution Astrophysical Observatory. Since the quality is uniformly high, the book would serve as a valuable resource for a reader interested in a slightly more technical overview of the frontiers of astronomy. -
“He Keeps Score for the Space Race.” BusinessWeek, October 30, 1965, 96-100. Written in the middle of the race to the moon, this article provides more insight into the high-profile role Lovell assumed as international arbiter of space missions. He is shown as opinionated but unquestionably competent. -
Henbest, Nigel, and Michael Marten. The New Astronomy. 2d ed. New York: Cambridge University Press, 1996. A delightful work, combining the talents of the two authors, respectively, astronomical consultant for New Scientist and director of the Science Photographic Library. Lavish color illustrations and lucid prose mark sections on each branch of astronomy, visible and invisible. For either browsing or serious study. -
Lovell, Sir Bernard. The Jodrell Bank Telescopes. New York: Oxford University Press 1985. Primarily discusses events from 1960 to 1982. MERLIN is described, as are many other ideas by Lovell, some of which were funded and some of which were not. -
_______. Out of the Zenith. New York: Harper & Row, 1973. This book describes the actual astronomical research done with the Big Dish in more technical detail. Covers events up to 1970. -
_______. The Story of Jodrell Bank. New York: Harper & Row, 1968. A first-person account of how Jodrell Bank Observatory began with two wooden huts and borrowed equipment. Lovell writes clearly of the years from World War II to the clearing of the debt on the Big Dish in 1960. It is anecdotal, thoroughly illustrated, and fascinating. A primary source. -
_______. Voice of the Universe. Rev. ed. New York: Praeger, 1987. A revision and updating of The Story of Jodrell Bank (1968) in which three more chapters are added: “Thirty Years On,” “The Mark IA Telescope,” and “MERLIN and the Future.” There are additional illustrations, and a broader perspective is given by the intervening years. -
“Lovell Hits Back at Jodrell Bank Study.” New Scientist, May 26, 1983, 523. A glimpse of the controversy in which Lovell found himself, even after his retirement as director of Jodrell Bank. Allows the reader to see something of the clamor and pressures involved in conducting a major research facility. -
Pfeiffer, John. “Big Dish—England’s Radio Telescope.” Science Digest 39 (January, 1956): 10-12. An interesting popular account of the construction of the 76-meter antenna, which focuses on the magnitude of the engineering finesse it required. Given the date of the article, the mention of computer control for the instrument seems almost anachronistic. -
Shapley, Harlow, ed. Source Book in Astronomy, 1900-1950. Cambridge, Mass.: Harvard University Press, 1960. A selection of sixty-nine contributions to illustrate the explosion of astronomical research during the first half of the twentieth century. An article entitled “The Beginning of Radio Astronomy” by Grote Reber succinctly gives the reader the immediacy of his groundbreaking work.
Reber Publishes the First Radio Maps of the Galaxy
Ryle’s Radio Telescope Locates the First Known Radio Galaxy
Hale Constructs the 200-Inch Telescope
Ryle Constructs the First Radio Interferometer
Radio Astronomers Transmit Radar Signals to and from the Sun
Discovery of the First X-Ray Source Outside the Solar System
Development of Very Long Baseline Interferometry