Radio telescope

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The Radiotelescopes, instead of receiving light waves, use large parabolic antennas to capture radio waves from stellar space.

On the cover you can se Lovell telescope, a fully steerable radiotelescope at Jodrell Bank, Cheshire, England.

The Radiotelescopes are indispensable

Many celestial objects, such as pulsars, galaxies, and quasars, emit radio frequency radiation and are visible in the radio region of the electromagnetic spectrum.

By examining the frequency and power of radio emissions from these objects, astronomers are able to broaden our understanding of the Universe more efficiently and precisely than with the images provided by light waves.

Radio telescopes are also used in projects like SETI and in monitoring unmanned space flights.

The observatories that have the most powerful radio telescopes are:

  • Jodrell Bank (USA),
  • RATOM-600 (Russia),
  • Effelsberg (Germany),
  • Big Ear (USA),
  • Arecibo (Puerto Rico),
  • VLA (USA),
  • GMRT (India) .

Still under construction, the largest of all, the LOFAR (Holland).

Beginnings of radio astronomy and the radiotelescopes

In 1937, the American engineer Grote Reber built  a first radio telescope, with a 9-meter antenna, in the courtyard of his house.

Grote Reber
Grote Reber pictured in 1947. Credit: NIST Archives, web “”

This is how “Radioastronomy” began, which is the observation of the sky by means of radio telescopes.

The typical size of a radio telescope antenna is 25 meters.

There are currently dozens of radio telescopes of this size operating in observatories around the world.

The interferometers and the Radiotelescopes

In the early 1950’s a technique called “interferometry” began to be used.

This is based on the physical principle that if two light waves that coincide in phase intersect, the resulting wave is amplified.

On the other hand, if the waves are in phase opposition, both waves cancel.

This combination of light from different telescopes or radio antennas is used to obtain higher resolution images.

The Cambridge Interferometer was a radio telescope interferometer built by Martin Ryle and Antony Hewish in the early 1950s to the west of Cambridge.

Cambridge Interferometer. The Radiotelescopes
The Cambrige Interferometer. Credit: web “”

In those years, with the Cambridge Interferometer, which had a distance of a mile between its two antennas, an analysis of the sky was carried out that gave rise to the famous 2C and 3C maps of radio sources.

In 1957, at the Jodrell Bank Observatory (at the University of Manchester, England) the world’s largest single antenna radio telescope in those years was put into operation: 76 meters.

It has played an important role in the search for quasars and pulsars.

Jodrell Bank. The Radiotelescopes
Jodrell Bank Radio Telescope. Credit: web “”.

In 1979, Jodrell Bank scientists announced the first detection of gravitational interference, confirming Einstein’s theory of “General Relativity.”

The largest single radio telescope in the world is the RATAN-600 (in Russia) with a circular antenna 576 meters in diameter.

The largest radio telescope in Europe is in Effelsberg, Germany.

It has an antenna 100 meters in diameter. In 2000 the Green Bank Telescope was inaugurated.

The Big Ear radio telescope was the largest in the United States in the 1950’s.

It was on the grounds of Ohio State University.

Big Ear. The Radiotelescopes
The Big Ear radio telescope, Ohio. Credit: Jerry Mason, Science Photo Library, web “”

It stopped working in 1997 and there is now a golf course and some 400 houses belonging to the former researchers of the project.

The Arecibo radiotelescope

Probably the radio telescope best known to the public is the Arecibo radio telescope in Puerto Rico.

In 1963, in the north of Arecibo Island (Puerto Rico), near the Equator in order to be able to observe all the planets of the Solar System.

Arecibo. The Radiotelescopes
The Arecibo Telescope was a 305 m spherical reflector radio telescope. Credit: web “”

The astronomical observatory called “National Astronomy and Ionosphere Center (NAIC)” was built, the which is administered by Cornell University and which houses the largest telescope built to date.

The Arecibo telescope has a spherical main antenna, 305 meters in diameter, built within a depression.

It is the largest and most curved converging antenna in the world, allowing the reception of much weaker electromagnetic waves, better than in any other telescope.

The antenna is fixed, but the receiver located on a 900-ton platform and suspended in the air, 150 meters, by 18 cables supported by three reinforced concrete towers, is at the focal point of the antenna, so that it intercepts all signals reflected from different directions by the spherical surface.

In December 2020, two cables holding the 900 tonnes of the telescope’s instruments broke above the 305-meter-diameter spherical antenna.

The falling of the cables irreparably damaged the antenna. It was an absolute disaster. The telescope was considered unstable and not repairable, so the institution announced its dismantling.

The famous telescope that allowed the first exoplanets to be discovered collapsed after 57 years of operation.

The Very Large Array telescope

Another well-known radio telescope is the Very Large Array (VLA), near Socorro, in New Mexico, United States.

This telescope is an interferometric system composed of a battery of 27 small antennas.

It is part of the National Radio Astronomy Observatory (NRAO) of the United States. Radio telescope

In 2007, the largest existing set of radio telescopes was the GMRT (Giant Meterwave Radio Telescope) located in India.


Bigger still is the LOFAR (LOw Frequency ARray).  It is in Western Europe (Holland and North Germany), consisting of 25,000 small antennas distributed in an area of ​​several hundred kilometers in diameter.

Lofar. The Radiotelescopes
This is part of the core of the LOFAR large radio telescope. Credit: web “”