How do astronomers listen to space?

In 1933, an engineer named Karl Jansky accidentally discovered that radio waves emanate not only from inventions made by man, but also from natural materials in space. Since then, astronomers have built better and better telescopes in search of cosmic radio waves, trying to learn more about where they come from and what they can tell us about our universe. While scientists can learn a lot from the visible light they detect with conventional telescopes, objects and events such as black holes, forming stars and planets, dying stars and many more can only be detected with radio telescopes. Together, telescopes capable of capturing different types of waves – from radio waves to visible light waves and gamma rays – paint a more detailed picture of the universe. But is it as easy to listen to the stars as it might seem at first glance?

This is what the MeerKat radio telescope looks like in South Africa. With its help, astronomers listen to space.


  • one Visible light
  • 2 What is a radio wave?
  • 3 Radio astronomy pioneers
  • 4 How do radio telescopes work?

Visible light

When we look at the night sky, we see the bright lights of the stars. If you live in a dark area far from cities, you can observe thousands of such objects. In this case, the individual points that you see are nearby stars. More than 200 billion of these celestial bodies exist in our galaxy alone. Outside the Milky Way, according to various estimates, there are at least 100 billion galaxies, each with its own 100 billion stars. Almost all of these stars are invisible to our eyes.

The visible light that the human eye perceives is only a tiny fraction of what astronomers call the “electromagnetic spectrum.” The more energetic photons are ultraviolet radiation, X-rays, and gamma rays (gamma rays have the highest energy). Lower energy photons are infrared and radio waves (radio waves have the lowest energy).

Human eye under a microscope.

The electromagnetic spectrum includes gamma rays, X-rays, ultraviolet radiation, infrared radiation, microwaves, and radio waves. Since human eyes only perceive visible light, we need special telescopes to capture the rest of this “spectrum” and then turn them into images and graphs.

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What is a radio wave?

Light is made up of tiny particles called “photons” that can act as both a particle and a wave at the same time. In visible light, photons have an average amount of energy, but when there is more energy, they turn into ultraviolet radiation, which we cannot see, but getting a sunburn is easy. With more energy, the photons turn into X-rays that pass right through us. But if the energy gets even more, they turn into gamma rays that come from exploding stars.

Radio astronomy has presented the world with the most detailed map of the Universe.

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In cases where photons have little energy, scientists talk about infrared radiation, which we perceive as heat, and researchers call the photons with the lowest energy “radio waves.” Interestingly, radio waves come from very strange places in space – the coldest and most distant galaxies and stars. They tell us about those corners of the universe, the existence of which we would not even have guessed if we used eyes or telescopes that perceive only the visible light spectrum.

Radio astronomy pioneers

It is also interesting that the world’s first radio astronomer was actually an engineer. In 1933, Karl Jansky worked on a project for Bell Laboratories, a laboratory in New Jersey named after Alexander Graham Bell, who invented the telephone. The first telephone system was developed there, which operated across the Atlantic Ocean. But when people first tried to call this system, they heard a hissing sound in the background at certain times of the day.

Bell Labs decided that the noise was bad for business and sent Karl Jansky to find out what caused it. The engineer soon realized that radio waves emanating from the center of the galaxy were disrupting telephone communications and causing interference. This is how, without knowing it, Yansky discovered a new, invisible Universe and became the world’s first radio astronomer.

The founder of radio astronomy Karl Jansky next to the antenna he built, which discovered the first radio waves emanating from space.

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How do radio telescopes work?

When astronomers point radio telescopes at an object in space, radio waves hit their surface. The surface of the telescope works like a mirror for radio waves and can be metal with holes in it (mesh), or solid metal such as aluminum.

The first mirror directs radio waves to a second “radio mirror”, which then directs them to a place called the “receiver.” This part of the radio telescope picks up radio waves and turns them into an image. Basically, a receiver does the same thing as a camera: converts radio waves into a picture.

Scientists have recently mapped hundreds of thousands of new galaxies using radio astronomy.

Когда астрономы ищут радиоволны, то наблюдают за другими объектами и событиями, чем когда ищут видимый свет. Все потому, что места, которые кажутся темными нашим глазам или обычным телескопам, в радиоволнах буквально светятся.

The corners of our universe where stars form, for example, are full of dust. This dust prevents light from reaching us, so that everything around looks like empty black space. But as soon as the radio telescope is directed to such areas, astronomers will have a delightful sight – through the dust you can see a star being born.

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