Radio Astronomy

In 1932, a Bell Labs researcher discovered radio signals pouring from the center of our galaxy. Astronomers didn’t know it, but a new science was about to be born.

This is June 6, on the birth of radio astronomy.

Grote Reber with his original 32 foot wide radio telescope first constructed at Wheaton, Illinois, in the summer of 1937. Karl Jansky pointing out where cosmic radio signals were first detected in the sky — at the center of the Milky Way galaxy.

In June of 1940, Grote Reber — an amateur radio operator and engineer — published a revolutionary paper describing his observations with a new type of telescope — a radio telescope. When you think of a telescope, you probably think of a tube-shaped object with lenses and mirrors. But that’s an optical telescope — designed to collect visible light. A radio telescope collects radio waves — the same basic phenomenon as visible light — but invisible to the human eye.

Eight years earlier, in 1932, a researcher at Bell Laboratories had discovered radio signals from space. Grote Reber was inspired by Karl Jansky’s idea of observing cosmic radio waves. Reber built his first radio telescope in his backyard in a Chicago suburb. To focus weak radio signals from space, he built a curved dish — 31 feet, or 9.5 meters wide. Many astronomers say that radio astronomy was born when his paper, titled “Cosmic Static” was published 60 years ago.

Since then, radio astronomers have discovered many things — including the glow left over from the Big Bang.

When you think of a telescope, you probably imagine a large tube-shaped object with lenses and mirrors that peers out from a hole in a metal dome. Before 1937, all serious telescopes would have looked something like this. Even today, many telescopes still look like this. They collect visible light, magnify it, and generate pictures that are essentially what the eye can see, just greatly magnified. You might think of them as complex magnifying glasses.

In 1937, a new from of telescope was born. Radio telescopes, unlike optical telescopes, are used to collect invisible data — radio waves. But radio waves and light waves are just different flavors of the same kind of energy — electromagnetism.

Many objects in space emit light waves — these are the ones we can see with optical telescopes or, if they’re bright enough, with our unaided eyes. Some of these objects also emit radio waves. A radio telescope gives us a more complete picture of what these objects are made of and what they’re doing. Perhaps most exciting are the objects which emit radio waves, but don’t emit light waves at all. With a radio telescope, these otherwise invisible objects pop into view.

Groundwork

If Grote Reber was the father of radio astronomy, Karl Jansky was the grandfather. It was his accidental discovery in 1932 that some radio signals picked up by radios on Earth don’t originate on Earth, but rather in space, that started Reber off on his attempt to build the first true radio telescope.

Jansky worked for Bell Laboratories. He was trying to identify the various natural causes of radio noise. Bell’s transatlantic radiotelephone operated on short radio wavelengths, which were very susceptible to radio noise. He found that lightning flashes were one source. The other major source became known as “cosmic static.” The main source of cosmic static — in the constellation Sagittarius — turned out to be the center of the Milky Way galaxy.

Jansky’s discovery was a very fortunate one. “It was a matter of chance that Jansky had chosen a frequency at which the galactic center emits copious amounts of radiation and at which the earth’s atmosphere is transparent. It was also a matter of chance that he was working at a time of sunspot minimum which occurs every 11 years. At sunspot maximum, the ionosphere would have blocked all radio waves from space at 20 MHz and signals from the Milky Way would have therefore been undetectable.” Malphrus, p. 6-7

The scientific establishment largely ignored Jansky’s discovery. His groundbreaking achievement was acknowledged years later by astronomers when they adopted a unit for the intensity of radiation from extraterrestrial sources called Janskys.

In 1953, Grote Reber wrote to Research Corporation: “As you know, Radio Astronomy started in this country over 20 years ago. Karl Jansky was not a very pushing type of person and he suffered from poor health. However, he did go around making addresses to various societies without any visible success. As he explained to me one time, the electrical engineers were not interested because they didn’t know any astronomy and couldn’t find anything useful in the subject. The astronomers were not interested because they didn’t know any electrical engineering and considered their present techniques adequate for studies of the universe. My subsequent experiences confirmed these reactions.”

Opening the Door to Radio Astronomy

Grote Reber, a young radio engineer in Wheaton, Illinois, was the first to follow up Karl Jansky’s 1932 announcement of the discovery of radio waves from space. Born December 22, 1911, Reber constructed the world’s first radio telescope, a 9.5-meter 31 foot wide dish in his back yard. The dish tilted only in one direction — north and south. Earth’s rotation swept the dish from west to east, allowing full coverage of the sky.

Reber’s 1940 publication of “Cosmic Static” in the Astrophysical Journal, which describes the results of his first two and a half years of observations, marks the beginning of intentional radio astronomy.

Reber built his first radio antenna and receiver on land his family owned “in a far western suburb of Chicago … free of the city’s sources of spurious signals.” His antenna was the first to use a paraboloid shape to focus weak radio signals. The choice of 31 feet for the width of the dish wasn’t determined by the wavelengths of radio signals he wished to study. He later explained in a lecture that it was because, “in building the supporting superstructure the longest lumber available at the hardware stores in Wheaton was twenty feet, dictating a maximum diameter of thirty one feet for the dish.” The dish could be titled by use of a differential gear from a Ford Model T truck.

60 Years of Radio Astronomy

Some historians of science mark the beginning of intentional radio astronomy in 1940, with publication of Reber’s “Cosmic Static” in the Astrophysical Journal.

Grote Reber laid the groundwork for many discoveries — that the sun is a source of radio waves Maarten Schmidt’s quasar or “quasi-stellar radio source” find Wilson Penzias’s discovery of the cosmic background radiation the discovery of pulsars rotating neutron stars and the discovery of some of the largest structures known — radio galaxies with jets streaming out in opposite directions. Radio astronomers have even detected atoms and molecules such as hydrogen in space.

“In the early 1950s, a grant of 15,000 by Research Corporation made possible Reber’s observations of cosmic radio noise and atmospheric phenomena from a mountaintop in Hawaii — to the amazement of those who had estimated that he would need ten times the amount he requested to carry out the project. ‘To fabricate the framework for his antenna, haul it 60 miles, and erect it at an altitude of 10,000 feet, with the help of a few men and do it for so little is just beyond comprehension,’ wrote the Maui school commissioner of Reber’s work. The data from this project and others conducted by Reber were equally impressive, and helped establish the new science of astronomy.” Science Invention and Society, p. 18

Reber created maps of radio sources in the sky, based on observations in Hawaii in the 1950s. From the 1960s to recent times, he has conducted his research in Australia.

Reber’s work included looking at the sun’s effect on the ionosphere and hence, how the sun affects transmission of radio signals on Earth. He discovered unidentified radio signals from Jupiter. He discovered radio signals emitted by the sun. He produced radio maps of the Milky Way galaxy and the entire sky.

“Reber was the first to express received radio signals in terms of flux density and brightness, first to find evidence that galactic radiation is non-thermal, and first to produce radio maps of the sky. Since then he has pioneered in very long-wavelength radio astronomy. Reber was the second astronomer after William Huggins to be awarded the Bruce medal for work performed as an amateur.”

What you have in your mind?