Reber Builds the First Intentional Radio Telescope Summary

  • Last updated on November 10, 2022

Grote Reber’s construction of the first reflecting radio telescope for the systematic study of radio emission from space marked the beginning of intentional radio astronomy.

Summary of Event

Intentional radio astronomy began in 1937 when Grote Reber built the first reflecting radio telescope at his home in Wheaton, Illinois, only fifty years after the discovery of radio waves by Heinrich Hertz in 1887 and five years after the first report of radio waves from space. Hertz had produced radio waves with a spark generator at about 50 million oscillations per second (50 megahertz) and measured a wavelength of about 6 meters (almost 20 feet), indicating a wave velocity equal to the speed of light (approximately 300 million meters, or 186,000 miles, per second). His work demonstrated that radio waves and light waves are both electromagnetic waves differing only in frequency and wavelength. Radio waves are the longest waves in the electromagnetic spectrum, which also includes infrared, visible light, ultraviolet, and X rays at increasingly higher frequencies and shorter wavelengths. [kw]Reber Builds the First Intentional Radio Telescope (June-Sept., 1937) [kw]First Intentional Radio Telescope, Reber Builds the (June-Sept., 1937) [kw]Intentional Radio Telescope, Reber Builds the First (June-Sept., 1937) [kw]Radio Telescope, Reber Builds the First Intentional (June-Sept., 1937) [kw]Telescope, Reber Builds the First Intentional Radio (June-Sept., 1937) Radio astronomy Radio telescopes Astronomy;radio Telescopes;radio [g]United States;June-Sept., 1937: Reber Builds the First Intentional Radio Telescope[09500] [c]Science and technology;June-Sept., 1937: Reber Builds the First Intentional Radio Telescope[09500] [c]Astronomy;June-Sept., 1937: Reber Builds the First Intentional Radio Telescope[09500] Reber, Grote Jansky, Karl G. Lovell, Bernard Hertz, Heinrich Marconi, Guglielmo

The early study of radio was directed toward the development of wireless communications, leading to transatlantic transmission and reception of radio signals in 1901 by Guglielmo Marconi. In 1932, Karl G. Jansky reported his accidental discovery of radio waves from space. At the Bell Telephone Laboratories in New Jersey, he built a rotating dipole-array wire antenna sensitive to 15-meter (49.2-foot) radio waves to study the static noise that interferes with radio communications. In addition to the usual atmospheric static, he detected a weak, steady hiss that appeared four minutes earlier each day. As this corresponds to the twenty-three-hour, fifty-six-minute apparent daily motion of the stars, he concluded that he was receiving cosmic radio noise from outside the solar system.

Jansky’s work was published in a series of scientific papers starting in 1932. His results made the front page of The New York Times, and a national radio network broadcast ten seconds of radio hiss from space. Despite this publicity, no scientist followed up on Janksy’s discovery until Grote Reber, a twenty-five-year-old radio engineer and amateur astronomer, decided to build a large parabolic dish for radio reception in the side yard at his home in Wheaton, Illinois, 40 kilometers (about 25 miles) west of Chicago. It was the first intentional radio telescope and the only one in operation until after World War II.

Reber was an avid radio amateur who built his first transceiver at age fifteen and began to communicate with other amateurs around the world. He received an electrical engineering degree in 1933 from what is now the Illinois Institute of Technology and began working for the Stewart-Warner Company in Chicago. After reading Jansky’s papers, he recognized the importance of his discovery. He also realized that greater progress could be made with equipment specially designed to measure cosmic static at radio frequencies. He began to plan the construction of a large reflecting dish with associated receiving equipment that could measure the detailed distribution ofradiation intensities throughout the sky at different wavelengths.

Although he had no outside support, Reber decided to build as large a reflector as he could in order to obtain maximum resolution (separation of sources) at radio frequencies. His reflector design also had the capability of tuning to different wavelengths by changing the antenna feed at the focus of the parabolic dish. He decided on a 6.1-meter (20-foot) focal length and a dish diameter of 9.4 meters (31 feet), based on the length of the longest two-by-fours available locally. Working with only a minimum of help from June to September, 1937, he completed his radio telescope at a cost of thirteen hundred dollars of his own money. This instrument remained in his yard for ten years; it was a source of amazement and wild rumors among local residents and visitors.

To minimize expense, Reber used a meridian-transit mounting that could be pointed up and down in a north-south plane (declination), while scanning east and west (right ascension) was provided by Earth’s rotation. The differential gear from a Ford Model T truck was used to change the elevation angle of the dish. The reflecting dish consisted of seventy-two radial wooden rafters cut to parabolic shape with a tolerance of about 0.5 centimeter (about 0.02 inch), with forty-five pieces of galvanized sheet metal screwed over the rafters to form the reflecting surface. The entire structure weighed nearly two tons.

The reflecting radio telescope built by Grote Reber in Wheaton, Illinois, in 1937.

(Library of Congress)

Using custom-made vacuum tubes from the University of Chicago and other radio components from his employer, Reber began with a receiver designed for the shortest possible operating wavelength of 9 centimeters (3.5 inches). This would give the best angular resolution and would be more sensitive to thermal radiation than at the longer wavelength detected by Jansky. Unfortunately, scanning at 9 centimeters gave no response, so he began to doubt that thermal radiation was the source of Jansky’s observations. By the summer of 1938, Reber had upgraded his receiver to detect 33-centimeter (13-inch) waves at a greater sensitivity, but still failed to find any radiation of celestial origin. A still longer wavelength could be conveniently detected with a cylindrical cavity made from a sheet of aluminum measuring 2 meters by 4 meters (approximately 6.6 feet by 13.1 feet), setting the operating wavelength at 1.87 meters (6.14 feet). A dipole antenna in the cavity resonator at the dish’s focus gave positive results by the spring of 1939, after two years of persevering work.

Reber did most of his observing from midnight to dawn to avoid interference from automobile ignitions. By April, the plane of the Milky Way crossed the meridian late at night, and it became apparent that our galaxy emitted 1.87-meter radio waves. The intensity of the cosmic radiation was determined by reading a microammeter at one-minute intervals while monitoring the audio signal to detect and remove periods of local interference. His initial results were published in February, 1940, in the Proceedings of the Institute of Radio Engineers, where he noted that his estimated intensity was far below that reported by Jansky at the 15-meter (49.2-foot) wavelength. This led Reber to the conclusion that the source of the cosmic radiation could be explained by interactions between electrons and positive ions (charged atoms) in an ionized gas rather than from thermal emission. Over the next five years, he obtained the first radio maps of the galaxy Milky Way galaxy;radio maps at two different wavelengths and identified a number of important radio sources in different parts of the galaxy.

As virtually the only active radio astronomer in the world, Reber operated his telescope in Wheaton for ten years before it was finally moved to a U.S. Bureau of Standards field station in 1947. The telescope was again relocated in 1960 to the National Radio Astronomy Observatory National Radio Astronomy Observatory at Green Bank, West Virginia, where it remains on public view and is occasionally used for demonstration purposes. In 1954, Reber moved to Tasmania, Australia, where he constructed a huge wire-antenna array telescope to measure radiation at a wavelength of 150 meters (approximately 492 feet) in the Southern Hemisphere.


The success of Reber’s pioneering radio telescope led to the rapid development of radio astronomy after World War II and the construction of increasingly larger and more sophisticated radio telescopes. Early work in radio astronomy was done by adapting radar scanning dishes retired from wartime service. Their electronic receivers were much more sensitive than the relatively simple devices used by Jansky and Reber. In fact, radio emission from the Sun was first observed accidentally by James S. Hey, when antiaircraft radars, operating between 4- and 8-meter (about 13- and 26-foot) wavelengths in England, experienced severe noise jamming on February 27 and 28 of 1942. Analysis of this phenomenon showed that the signals came from the Sun during unusual sunspot activity, but publication was withheld until after the war. Reber also detected solar radio emissions in 1943.

One of the first applications of radar to radio astronomy began in 1946 at Jodrell Bank, an experimental botanical site of Manchester University. Here, a group led by Sir Bernard Lovell used radar astronomy to study daytime meteor activity in great detail, even though it was invisible to ordinary sight. In 1947, they constructed a fixed, upward-looking parabolic reflector, 66 meters (216.5 feet) in diameter, with a reflecting surface consisting of wire mesh spread over a frame on the ground. This instrument was limited to vertical reception, with scanning mainly from Earth’s rotation. Lovell soon began to plan a giant fully steerable reflector that could explore radio phenomena throughout the universe. Construction of the 76-meter (249.3-foot) radio telescope at Jodrell Bank Experimental Station took six years, with the turret rack of a battleship to move the huge dish. It was designed to operate at 21 centimeters (about 8.3 inches) after it was discovered that interstellar atomic hydrogen radiates at that wavelength. The telescope was completed in 1957, in time to track the first human-made satellite, Sputnik 1. This instrument gave productive results in many investigations, including emissions from the Sun, the galaxy, and several discrete radio sources.

In the United States, the National Radio Astronomy Observatory began operation at Green Bank, West Virginia, with a 26-meter (85.3-foot) dish in 1959, followed by a 91-meter (298.6-foot) transit telescope in 1962 and a 43-meter (141.1-foot) steerable telescope in 1965. For more than twenty-five years, the 91-meter telescope, with its wire-mesh reflecting dish, was the largest movable telescope in the United States until it collapsed from metal fatigue in 1989. In 1970, a 100-meter (328.1-foot) fully steerable radio telescope was completed at Effelsburg near Bonn, West Germany, and in 1963, a 305-meter (1,000-foot) fixed bowl built of wire mesh was constructed in a natural valley near Arecibo, Puerto Rico.

Larger telescopes provide sharper images, but the best resolution can be achieved through the electrical connection of two or more radio telescopes in an array; this configuration gives a resolving power equivalent to a single dish with a diameter equal to the size of the array. The Very Large Array (VLA) in the high desert near Socorro, New Mexico, began operation in 1980 with twenty-seven dishes, each 25 meters (about 82 feet) in diameter, forming a Y-shaped array 27 kilometers (about 16.8 miles) long, with a resolution comparable to that of the best optical telescopes. Radio astronomy Radio telescopes Astronomy;radio Telescopes;radio

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Abell, George O., David Morrison, and Sidney C. Wolff. Exploration of the Universe. 6th ed. Philadelphia: Saunders College Publishing, 1991. Standard college astronomy textbook includes a good chapter on radio telescopes that presents some discussion of Reber’s work. Describes many of the most important radio telescopes and features a good variety of photographs.
  • citation-type="booksimple"

    xlink:type="simple">Burke, Bernard F., and Francis Graham-Smith. An Introduction to Radio Astronomy. 2d ed. New York: Cambridge University Press, 2002. Authoritative graduate-level text provides an introduction to radio telescopes as well as an overview of radio astronomy. Includes references, index, and an appendix on the origins of radio astronomy.
  • citation-type="booksimple"

    xlink:type="simple">Hey, J. S. The Evolution of Radio Astronomy. New York: Science History Publications, 1973. Useful history of radio astronomy by one of the pioneers in its development. Describes the work of Jansky and Reber as well as the rise of radio astronomy after World War II. Includes illustrations and references.
  • citation-type="booksimple"

    xlink:type="simple">Malphrus, Benjamin K. The History of Radio Astronomy and the National Radio Astronomy Observatory: Evolution Toward Big Science. Melbourne, Fla.: R. E. Krieger, 1996. Presents the history of the field of radio astronomy along with that of one of the world’s most important radio astronomy observatories. Accessible to both lay readers and readers with science backgrounds.
  • citation-type="booksimple"

    xlink:type="simple">Spradley, Joseph L. “The First True Radio Telescope.” Sky and Telescope 76 (July, 1988): 28-30. Introductory article on Reber’s background and work describes the design, construction, and operation of the first intentional radio telescope. Includes photographs of the telescope and the original model used in its design.
  • citation-type="booksimple"

    xlink:type="simple">Sullivan, Woodruff T., III, ed. The Early Years of Radio Astronomy: Reflections Fifty Years After Jansky’s Discovery. 1984. Reprint. New York: Cambridge University Press, 2005. Collection of articles by the pioneers of radio astronomy on the field’s early development. Includes a 1958 article by Reber, originally published in Proceedings of the Institute of Radio Engineers, titled “Early Radio Astronomy at Wheaton, Illinois” and an article by Lovell titled “The Origins and Early History of Jodrell Bank.” Features many historical photographs.
  • citation-type="booksimple"

    xlink:type="simple">Verschuur, Gerrit L. The Invisible Universe Revealed: The Story of Radio Astronomy. 2d ed. New York: Springer-Verlag, 1987. Provides good description of the results of radio astronomy with more than one hundred photographs and radio contour maps. Concluding chapters give a history of the field since Jansky and Reber and present an overview of the most important radio telescopes.

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