The Radio Telescope

by Amy Schloerb

The radio telescope can see much more than an optical telescope. Things that have been discovered in the universe would not have been discovered if it were not for the radio telescope.


The inventor of the radio telescope is Grote Reber. He was born in Wheaton, Illinois, in 1911. As an adult he was an American engineer and amateur astronomer. In 1937 in his backyard he built the world's first radio telescope. The dish was a mere 31 feet across. The telescope could move both the dish and the mount. This is called fully steerable. After three years of working with his radio telescope, Grote Reber wrote a report concluding that the Milky Way actually gives off radio raves. He went on to lead experimental microwave research in Washington D.C.

Although Grote Reber alone built the world's first radio telescope, he could not have done it without the findings of a man named Karl Jansky. Karl Jansky was born in 1905 and worked at a telephone company and had to build a radio antenna to find out why there was too much static on long distance telephone calls. It turned out to be radio waves coming from space. As a result of this, Jansky wrote a report on the radio waves he discovered. Grote Reber being highly interested in astronomy found Jansky's work and decided to continue it. Thus building the radio telescope.

Jansky and Reber both built a radio antenna or a radio telescope. Being different people they each built their instrument out of different things. Jansky built his radio antenna mostly out of wood. It has 21 foot metal poles and reflectors. It was mounted on a track with tires. Grote Reber on the other hand built his radio telescope more like people do today. It had a dish which was made of wire screen. More commonly used today is glass or metal.


There are many different kinds of light. There's Visible, Ultra Violet, Infrared, X-rays [ the shortest ] and radio [ the longest ]. A wave length is measured from one crest to another. This would be a short wave length:

Image of short wavelength.

This would be a long wave length:

Image of long wavelength.

Frequency measures the number of waves. The higher the frequency the shorter the wave length and the lower the frequency the longer the wave length:

Image of frequency vs. wavelength.

The amplitude of a wave is measured by how high or low the wave goes from the middle. The higher the amplitude the more energy the wave carries.

Image of amplitudes.


The radio telescope is used to detect most of the things that an optical telescope can not see. The comments of a radio telescope are the same as in a car radio. The both have the antenna, the receiver, the detector, and the computer or speaker.

Diagram of radio telescope components.

The radio telescope's dish has to be very large. The reason for this is that the radio telescope detects very weak signals. So it has to be big to do that. The dish of a radio telescope collects all the waves at the wave length that the receiver is tuned to. After the dish gets the waves they bounce to the antenna or feed if you want to be technical about it. During that action the waves are concentrated so they can be turned in to electrical signals. Then the receiver comes into play. it is tuned to one wave length by an astronomer. The radio telescope can only detect the wave length that the receiver is tuned to. The receiver also amplifies the waves and changes them in to electrical signals. [ One more thing ] The receiver must be kept very cold. If it is not, there will be a lot of unnecessary static and you cannot see what you want to see what you want to see as well. Next cones the detector. The detector measures the amount of energy in the wave so the computer knows how to make the picture. After going through the detector signal moves on to the computer. The computer records the signal and stores it. The computer cam make a picture by having the radio telescope go back and forth across an object. By doing that the radio telescope can get good details [ that it wouldn't be able to see otherwise ] so the computer can make a picture.

When people decide to build a radio telescope they can't just build it any old place, they have to build it away from any things that give off radio waves. [ radio and T.V. stations are not good ] The reason for this is that the radio and T.V. station's waves might mix in with the incoming waves.


One way of getting very fine details is to use an array. An array is a lot of radio telescopes that are connected to one another. When you do this you get a very powerful radio telescope. Arrays can also join up to each other all over the world and get even finer detail. The only down side of an array is it is very hard to see very faint objects.


Since the time of Grote Reber the radio telescope has gotten much bigger. Now a days a big radio telescope would be about ninety-two meters. Compare that to Grote Reber's measly ten meter radio telescope. Here is a chart of some other famous radio telescopes:

Size Location Time Facts
250 feet (83 m) Jodrell bank, England 1957 .
1,000 feet (333 m) Arecibo, Puerto Rico 1960's World's biggest (covers a valley)
78,000 feet (surface area) National Radio Astronomy Observatory, Green Bank, Maryland . U.S. Biggest (fell down)
328 feet West Germany 1971 Biggest fully steerable
82 feet (each) New Mexico 1970's An Array (each weigh 200 tons)
3 miles long Cambridge, England at Mullard Radio Astronomy Observatory . An Array (8 radio telescopes)
210 feet (70 m) New South Wales at Parkes Observatory . .
45 m Pune, India . An Array (being built Cost: $15,000,000 they think)

The radio telescope has already helped us to find many fascinating things. If we chose to continue the works of Karl Jansky and Grote Reber, we will be able to find things for years to come.


Macaulay, David, The Way Things Work, Dorling Kindersley limited, Great Britain, 1988

Schloerb, Peter, interview in January and February 1996

Compton's Interactive Encyclopedia, Simon and Schuster, 1995

Branley, Franklyn, The Electromagnetic Spectrum, Fitzhenry and Whiteside limited, Toronto, 1979

Kerrod, Robin, The Universe, Great Britain, Sampson Low, 1975

Science, 22 April, 1994

Heiserman, Dave, Radio Astronomy for the Amateur, Tap Books, 1975