Light pollution affects most of the planet's telescopes

For centuries, the astronomical observatories were in the cities.

The astronomers observed the stars from the center of Berlin, London, Madrid... The increasing illumination of the cities forced them to be removed from there.

First to the outskirts and then further and further away and, especially, higher and higher.

The active celestial viewpoints in Europe or the United States are on the summits, such as those of Calar Alto, in Almería, or that of Roque de los Muchachos, in La Palma.

But even that isn't saving them from light pollution: A study of nighttime brightness over the sky from the planet's major observatories shows that most have so much light that it blinds their telescopes.

The research, developed by researchers from Chile, Italy and Spain, has used data collected by satellites during their night passage over the sky from all observatories with telescopes of at least three meters in diameter.

The results of their work, recently published in the specialized journal of the

British, show that only seven of the 28 observatories have a brightness at the celestial zenith below 1% of the natural brightness of the sky.

This zenithal glow (above the observatory's vertical) is the main quality parameter of the night sky.

But the authors of the study took others into account, such as the average brightness in the entire celestial hemisphere or the existing light in the 30º above the horizon line.

This is the minimum position that most telescopes can operate at, which cannot see below there.

The horizon is also the area where there is more light pollution.

Counting only on this parameter, only one of the observatories would be free of light pollution, in Namibia.

“If you have a bright sky, they need more time and more work to get the data to the same quality.

It's like the telescope shrinks

Fabio Falchi, researcher at the Istituto di Scienza e Tecnologia dell'Inquinamento Luminoso, Italy

Fabio Falchi, a researcher at the University of Santiago de Compostela and the Istituto di Scienza e Tecnologia dell'Inquinamento Luminoso (Italy), is the main author of this research.

Light pollution is a relative concept in which the reference is the degree of darkness in a natural environment.

"The sky of Madrid is 40 times brighter than the natural sky", he gives an example.

Observatories can't operate at those levels of nighttime brightness, let alone much less.

“If you have a bright sky, they need more time and more work to get the data they get to the same quality.

It's like the telescope is shrinking.

So if you have a 12-meter one, it would become a 9- or 8-meter one,” says Falchi.

The best place to see the stars is in the Namibian desert.

This is not a professional observatory, but one that has been set up as a tourist attraction by amateur astronomers, the Tivoli Southern Sky guest farm.

Among the professionals, other observatories located in southern Africa, lost in the Amazon jungle and those of the Atacama desert, in Chile, stand out.

The three with the worst scores are those of Chapultepec (Mexico), Púlkovo (Russia) and Mount Wilson (USA).

They are observatories that are more than a century old and, then, their location was ideal: outside the cities, but not too far.

The problem is that humans have not stopped expanding and increasing their lights.

Today, these centers are too close to Mexico City, St. Petersburg, and Los Angeles, respectively.

Usually,

Alicia Pelegrina is a member of the sky quality office of the Instituto de Astrofísica de Andalucía (IAA).

For her, "light is the messenger of the celestial bodies, but if the sky, the background, is not dark, we only see the brightest objects."

For this reason, Pelegrina recalls, "astronomers were the first to warn of light pollution, a pollution that is as much an environmental problem as that caused by hydrocarbons."

The IAA researcher recently published a book on the damage that human lights are doing to the sky, but also to life on Earth, whether natural or human health itself.

This starry sky can be seen from an observatory set up by amateur astronomers in the Namibian desert, where they rent their telescopes.Fabio Falchi

The problem is that the excess of light has been coupled with progress, with progress.

Pelegrina exemplifies this with the Granada astronomical observatory.

The Jesuits built it at the beginning of the last century in La Cartuja, then on the outskirts of the city.

But in 1968 they had to take it to the Mojón del Trigo, already in the heights of the Sierra Nevada.

In 1981 they had to move it even higher, to Loma de Dílar, on the Veleta peak, the third highest mountain in the Iberian Peninsula.

"We have associated light with positive aspects, with progress, with progress, and now we must change the paradigm," says Pelegrina.

The University of Exeter researcher Alejandro Sánchez has spent years studying and denouncing light pollution.

His most recent work shows that, instead of decreasing, the light that humans project into the sky is increasing.

"Throughout the planet, the minimum night brightness has increased by 49% since 1992," recalls Sánchez.

Minimal because "the satellites we use to measure are blind to blue light," he adds.

And it is in this range of the spectrum that the vast majority of LED lights that are leading the transition to this technology operate.

In fact, in another work, with data from the International Space Station, which does have instruments that record the different spectrums of light, they have seen an increase of "11% in light pollution in the green and another 24.4% in the blue” in 2020 compared to 2012.

In Europe and the United States, the blame for the increase would be in an erroneous "choice of blue LED light, instead of amber, which is more natural," says Sánchez.

Also, the improvement of living conditions in giants like India and China has translated into more light pollution.

There is also a source of pollution to consider: artificial satellites.

“They fill the sky with light at sunset and dusk, and when it is still night on Earth, but up there the Sun shines on them,” says Sánchez.

They work like mirrors, reflecting sunlight and brightening everything around them.

And, as this researcher recalls, "Elon Musk wants to put another 30,000 satellites in orbit."

Not even the observatories taken to the deserts of Chile or Namibia will be able to escape.

You can follow

Subscribe to continue reading

Read without limits

Keep reading

I'm already a subscriber