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The end came with a huge bang: On December 1st - after several minor damage in the previous days - an instrument platform of the Arecibo radio telescope in Puerto Rico fell 135 meters and destroyed the dish-shaped radio antenna with a diameter of 300 meters below.
It was the end of an era: After commissioning in 1963, Arecibo was the largest radio telescope in the world for half a century.
"For us astronomers, it was a workhorse that reliably delivered data," emphasizes Anton Zensus, Director at the Max Planck Institute for Radio Astronomy in Bonn.
In particular, the large collection area of the facility, which was built in a basin in Puerto Rico, was important to the researchers.
In 2016, the FAST radio telescope with a diameter of 520 meters went into operation in China and replaced Arecibo as the largest radio telescope in the world.
The gigantic antenna is now also available to astronomers from other countries for their research.
“But such instruments always have a strong national character,” says Zensus.
It is therefore understandable that US astronomers are calling for a quick replacement.
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In general, radio astronomy has developed considerably since Arecibo was built: Today there are numerous large antenna systems that cover special wavelength ranges.
LOFAR, for example, the “Low Frequency Array” installed throughout Europe, consists of over 10,000 antennas for long-wave meter waves.
Or the Atacama Large Millimeter / Submillimeter Array ALMA on the 5000 meter high Chajnantor Plateau in the northern Chilean Andes.
It consists of a total of 66 antennas with a diameter of seven to twelve meters and covers the wavelength range around one millimeter.
Construction of a new, even bigger facility will begin next year: The Square Kilometer Array (SKA) has a collecting area of one square kilometer - hence its name - and consists of thousands of antennas in Australia and South Africa.
The gigantic facility, which should be completed by the end of the decade, should not only observe a wide range of wavelengths, but also exceed the sensitivity of current facilities by fifty times.
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Radio astronomers are concerned about the creation of large satellite constellations such as Starlink.
With up to 30,000 satellites, this network, operated by the US space company SpaceX, will offer high-speed internet access all over the world.
But the radio signals from Starlink disrupt the astronomers' sensitive radio antennas considerably.
That is why some researchers in the USA propose to build a replacement for Arecibo on the back of the moon, because there a radio telescope would be shielded from earthly interference.
The Starlink satellites are also becoming a nuisance for astronomical observations in visible light: It is increasingly common for one of the satellites to rustle through the image while observing and the sunlight it reflects to ruin the data.
“I'm definitely worried about Starlink,” admits Laura Kreidberg, director at the Max Planck Institute for Astronomy in Heidelberg.
"But there are ways to mitigate the harmful effects of the satellites."
China starts alien search with mega-telescope "Fast"
The world's largest radio telescope has now been put into operation in China.
It is supposed to intercept gravitational waves and radio frequency radiation.
His name "Fast" stands for "Five-hundred-meter Aperture Spherical Telescope".
Source: The World
In close contact with SpaceX - the company appears to be quite cooperative - astronomers are trying to keep the damage caused by changes in orbits and less strongly reflective surfaces to a minimum.
"Starlink is frustrating," says Kreidberg.
"But that doesn't mean it is all over for ground-based observatories."
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That is why the sky researchers are optimistic about a huge increase in the performance of optical telescopes on earth.
The currently largest telescopes such as the four mirrors of the Very Large Telescope of the European Southern Observatory ESO in Chile or the two American Keck telescopes in Hawaii have mirror diameters in the range of eight to ten meters.
But before the end of this decade, two much larger telescope giants are expected to receive their first light from the depths of the cosmos.
The Thirty Meter Telescope with its 30-meter mirror consisting of 492 segments is being built on the Canary Island of La Palma and is a joint project between the US research company Caltech and Canadian universities.
The Extremely Large Telescope (ELT), which is being built by the European Southern Observatory in Chile, is even bigger: composed of 798 hexagonal mirror elements, it has a diameter of 39 meters.
Source: WORLD infographic
Two developments in particular make it possible to build telescopes of this size: On the one hand, the use of ever thinner mirrors, and on the other hand, the combination of many small mirror segments instead of one massive individual mirror.
Thin mirrors - the segments of the ELT are only five centimeters thick - reduce the weight and thus make it easier to store and control the telescopes.
However, they have the disadvantage that they are easily deformed.
However, advances in computer technology mean that these deformations can be permanently compensated for using a large number of small motors.
The ELT is equipped with 6000 such actuators, which correct the shape of the mirrors a thousand times per second.
Even more: By specifically adapting the shape of the mirror, it is even possible to compensate for image disturbances caused by turbulence in the atmosphere.
The earth's atmosphere is a nuisance to astronomers not only because of this turbulence, but also because it absorbs some of the light coming from space.
These problems can only be completely avoided by stationing telescopes in space - but that is expensive.
Shooting a 30-meter-class telescope into space is currently neither technically nor financially feasible.
But now a whole series of smaller telescopes are orbiting the earth, often specializing in tasks such as searching for planets near other stars.
The most famous space telescope is the now 30-year-old “Hubble” - which is to have a modern successor this year: The start of the “James Webb Space Telescope” (JWST) is scheduled for October 31st.
It can collect around five times more light than “Hubble” and is also more efficient in the infrared range.
This range of radiation offers astronomers, for example, insights into the formation of planets.
In contrast to “Hubble”, the “JWST” does not orbit the earth after its start, but flies to a location 1.5 million kilometers away on the far side of our planet.
At this so-called Lagrange point, the telescope is not only protected from earthly disturbances, but can also orbit the sun together with the earth with almost no drive.
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In just a few years, astronomers will have a whole series of new large-scale instruments at their disposal to explore the cosmos.
There are two main questions to which they are looking for an answer: What is the universe made of - and is there life somewhere in the depths of the universe?
All the visible matter - stars, planets, gas clouds - makes up only a fraction of the universe according to today's knowledge: just 4.6 percent.
The main components are dark matter and dark energy: although both influence cosmic development, researchers do not yet know what it is.
An answer to the second question would be even more important.
Some researchers estimate that there could be around 300 million habitable planets in our Milky Way galaxy alone.
The next generation of telescopes could provide evidence of biological activity on distant planets.
And perhaps the great radio telescopes will soon receive signals from distant technical civilizations - humanity would no longer be alone in the infinity of the cosmos.