Radio Astronomy: Part 1

Parkes Radio Telescope

Radio Astronomy

Radio Astronomy has become a key part of modern astronomical research.

It has literally given us a new view of the universe.

So what is radio astronomy?

What is a radio astronomy observatory like?

Parkes Radio Telescope

Parkes Radio Telescope, NSW, Australia

Photo: Dennis Ashton


Until the 1930s, our view of the universe came through light.

We saw planets, stars, nebulae and galaxies by their visible light.

But objects in space give out radiation in other parts of the electro-magnetic spectrum.

Radio waves are longer than visible light and invisible to our eyes.

They can be detected by radio receivers on the ground.

Electromagnetic Spectrum

 Image: NASA

In 1933, engineer Karl Jansky was working for Bell telephones in America.

He was investigating radio interference on trans-Atlantic phone lines.

The detector he built was a rotating radio antenna, ‘Jansky’s merry-go-round’.

The antennae were 30 metres across and 6 metres high.

They turned on Ford model-T wheels.

By moving the array, Jansky could more easily pinpoint the source of radio noise.

Karl Jansky

Karl Jansky’s radio antenna: Photo courtesy of NRAO/AUI


In 1933, Jansky found radio signals coming from the Milky Way.

They were strongest from the galaxy’s centre, in the direction of the constellation Sagittarius.

Jansky wrote several papers on his findings but they were not followed up.

Professional observatories were wary of the new science.

And the great depression in the USA deterred companies, including Bell Telephones.


However, Jansky’s findings inspired Grote Reber, an amateur astronomer and radio ham.

Reber built a radio telescope with an 9-metre dish at his home in Wheaton, Illinois, USA.

Reber telescope

Grote Reber’s radio telescope. (public domain)


In the early 1940s, Reber published a sky survey of radio sources.

They included Cygnus A and Cassiopeia A.

Cygnus A is now known to be a radio galaxy.

Cassiopeia A is a supernova remnant.

And what of Karl Jansky’s discovery of radio emission from the Milky Way?

It actually comes from material falling into a supermassive black hole at our galaxy’s centre.

This radio source is called Sagittarius A*.

Radio Telescopes

Radio telescopes have two advantages over optical instruments.

They work in daylight because radio signals are not swamped by sunlight.

And they are not dependent on weather conditions because radio signals penetrate through cloud.


They have disadvantages too.

Ideally they should be located away from urban areas and their radio noise.

This is the equivalent of optical light pollution.

And they have to be big.

The biggest professional optical telescopes have mirrors 8 to 10 metres in diameter.

Radio telescope dishes are many times bigger.

The largest, FAST in China, has a dish 500 metres across!


Radio wavelengths which reach Earth are long, from a few centimetres up to 10 metres.

So radio telescopes must also be big to collect the long wavelengths.

The most familiar radio telescope is the parabolic dish, like the one Grote Reber designed.

Less spectacular are antennae based on Karl Jansky’s original idea.

They often resemble fields of chicken wire.


Famous radio telescopes

I have been fortunate enough to visit several of the world’s most famous radio observatories.

Together, they illustrate important aspects of radio astronomy.


Jodrell Bank, UK

Jodrell Bank in Cheshire was established by Sir Bernard Lovell in 1945.

It is home to the iconic Lovell radio telescope.

The dish is 76 metres (250 feet) across, making it the third largest steerable dish in the world.

It gained national prominence in 1957, when it tracked Sputnik 1, the world’s first artificial satellite.

Since then it has been at the forefront of British astronomical research.

Lovell Telescope

Jodrell Bank Lovell Telescope at night.     Photo: Dennis Ashton


Parkes, Australia

In 2009, I visited Parkes Radio Observatory in New South Wales, Australia.

The main dish is 64 metres (210 feet) across, the second largest in the southern hemisphere.

Parkes Radio Telescope

Dennis at Parkes Radio Observatory, NSW


Parkes Observatory was founded in 1963.

Since then it has conducted several all sky surveys of the southern sky.

It has also discovered over half of all known pulsars.

In July, 1969, Parkes Observatory achieved international fame when it broadcast pictures from the first Moon landing.

The movie The Dish recounts how Australians played a key part in the Apollo programme.

The Australian observatory has also helped in tracking robotic missions, including the Voyager probes.


The Very Large Array

On a trip to the USA in 2004, I visited the Very Large Array, VLA.

The VLA is located in the dry San Augustin Plain in New Mexico.


Dennis at the VLA, New Mexico, USA


As its name implies, the VLA is a collection of radio telescopes.

Each steerable dish is 25 metres across and weighs 230 tons.

There are 28 dishes, each one a powerful instrument in its own right.

The telescopes are arranged in a huge ‘Y’ shape on the desert floor.

They are on rails so that their distance apart and configuration can be altered.

This array is electronically linked so, in effect, it becomes a telescope as large as the spread of dishes.

At its biggest, the VLA creates a telescope 22 miles across!

This hugely increases the resolution, the clarity and detail of the observations.

Its discoveries have varied from the detection of ice on Mercury to gas flows around supermassive black holes.

The VLA was the location in the movie Contact where Dr Ellie Arroway, played by Jodie Foster, first detected an alien signal.


HartRAO, South Africa

Finally we take a look at the Hartebeesthoek Radio Astronomy Observatory, HartROA,  in South Africa.

It is located about 50km west of Johannesburg, in the Magaliesberg mountains.

NASA built the observatory in 1961, when it was known as Deep Space Tracking Station 51.

It tracked many robotic space probes, including Mariner 4 at Mars.

South Africa’s National Research Foundation has now taken over running the observatory..


HarteRAO, the walk to the dish. Photo; Dennis Ashton


I visited HarteRAO in the year 2000, on a trip to South Africa with my mobile planetarium.

The staff invited our group to climb up to the 26-metre dish, which they had placed in its horizontal position.

It was a somewhat scary climb but finally we reached the metal gridwork of the dish.

The surface was surprisingly firm and I walked along the main struts to the edge.

It was high and so was I. My walk in a radio telescope dish was a memorable experience.

HartRAO dish

Dennis in the HartRAO dish.


Visit a Radio Observatory

Jodrell Bank in Cheshire is now open to visitors after a Covid shut down.

You can see the Lovell Telescope up close and listen to talks about it’s work.

The visitor centre also offers a range of activities.

Click here for details.

Next time

In our next blog, we will take a look at how radio telescopes receive and display signals from space.

We’ll also take a closer look at important discoveries made through Radio Astronomy.


The author: Dennis Ashton is a Fellow of the Royal Astronomical Society and a Wonderdome presenter.


Would you like to hear more  Astronomy news?

Do you want to to find out about our upcoming public events?

Follow WonderDome Portable Planetarium on Twitter and Facebook or go to our web site!