Telescopes from the Ground Up

Era of Radio Telescopes

Reber’s Radio Telescope

A devoted amateur opens up a new field

The public was excited over Karl Jansky’s discovery in 1932 of radio waves coming from the sky. Newspapers picked up the story, and radio stations around the United States took a moment to celebrate the discovery by broadcasting the sound of this static from the stars.

However, astronomers and scientists didn’t pay much attention. The exception was one amateur astronomer, Grote Reber. Reber, an American radio engineer, read about Jansky’s work and was fascinated. He wanted to go beyond the steady hiss Jansky had heard. He wanted more detail, and for that, he would need to build a telescope to pick up radio waves.

Catch the wave

In 1937, Reber built a telescope with a dish in the shape of a parabola — just like the mirrors of other reflecting telescopes. The 31-foot (9-meter) iron dish could be turned north and south, but not east or west, so Reber had to wait for the Earth’s rotation to bring the object he wanted to observe into the view of the telescope. The dish directed the radio waves toward a receiver.

Radio waves have their advantages. Like visible light, they pass through Earth’s atmosphere without being absorbed, but they are not distorted by the atmosphere, as visible light can be. In addition, there isn’t much radio-wave radiation in nature to interfere with observing the radio-wave radiation from the sky. However, astronomers have to watch out for man-made radio signals, as Reber discovered.

• Reber’s Telescope1937
• Very Large Array1980

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