Light pollution affects most planetary telescopes | science

For centuries, astronomical observatories have been located in cities. Astronomers observed the stars from the center of Berlin, London, Madrid … The increased illumination of cities forced them to move away from there. First to the outskirts, then further and further, especially higher and higher. Active heavenly viewpoints in Europe or the United States are found on peaks, like those at Calar Alto, in Almeria, or those of Roque de los Muchachos, in La Palma. But even this does not save them from light pollution: a study of the night brightness over the sky from the main observatories of the planet showed that most of them contain so much light that they block their telescopes.

The research, developed by researchers from Chile, Italy and Spain, used data collected by the satellites during their nighttime passes over the sky from all observatories with telescopes at least three meters in diameter. The results of their work were recently published in The specialized magazine affiliate Royal Astronomical Society The British showed that only seven of the 28 observatories had a peak-sky brightness of less than 1% of the normal sky-brightness. This bright glow (above the observatory’s perpendiculars) is the main quality standard for the night sky. But the study’s authors took into account others, such as the average brightness for the entire celestial hemisphere or the light within 30 degrees above the horizon line. This is the minimum position that most telescopes can operate at, which cannot be seen below. The horizon is also the area where there is more light pollution. Relying solely on this parameter, only one of the observatories will be free of light pollution, in Namibia.

“If you have bright skies, they need more time and more work to get the data just as good. It’s like shrinking a telescope.”

Fabio Falchi, researcher at the Institute of Applied Sciences and Technology, Italy

Fabio Falchi, researcher at the University of Santiago de Compostela and Istituto di Scienza e Tecnologia dell’Inquinamento Luminoso (Italy), lead author of this research. Light pollution is a relative concept in which the reference is the degree of darkness in a natural environment. He gives an example: “The sky in Madrid is forty times brighter than the natural sky.” Observatories cannot operate at those levels of nighttime brightness, let alone much lower. “If you have bright skies, they need more time and more work to get the data they’re getting at the same quality. It’s like the telescope is shrinking. So if you have 12 meters, it becomes 9 or 8 meters,” he says. Valche.

The best place for stargazing is the Namibian desert. This is not a professional observatory, but an observatory created as a tourist attraction by amateur astronomers, the Tivoli Southern Sky guest farm. Among the specialists, the other observatories located in South Africa, lost in the Amazon jungle and those in the Atacama Desert, in Chile, stand out. The three with the worst results are Chapultepec (Mexico), Belkovo (Russia) and Mount Wilson (USA). They are observatories over a century old, hence, their location was perfect: outside the cities, but not too far away. The problem is that humans have not stopped expanding and increasing the lights. Today, these centers are very close to Mexico City, St. Petersburg, and Los Angeles, respectively. In general, telescopes in mainland Europe and the United States have a lot of night light.

Alicia Pelegrina is a member of the Sky Quality Bureau at the Instituto de Astrofísica de Andalucía (IAA). For her, “light is the messenger of the heavenly bodies, but if the sky, the background, is not dark, we see only the brightest things.” For this reason, Pellegrina recalls, “astronomers were the first to warn of light pollution, pollution that is as much an environmental problem as hydrocarbons.” An IAA researcher recently published A book about the harm that a person causes to lights They do in heaven but also life on earthWhether it is natural or human health itself.

The problem is that an excess of light has been associated with progression and progression. Pellegrina exemplifies this at the Granada Astronomical Observatory. It was built by the Jesuits at the beginning of the last century in La Cartuja, then on the outskirts of the city. But in 1968 they had to move it to Mojon del Trigo, already in the highlands of the Sierra Nevada. In 1981, they had to move it even higher, to Loma de Dilar, to the top of Veleta, the third highest mountain in the Iberian Peninsula. “We associated light with positive aspects, with progress, with progress, and now we have to change the paradigm,” says Pellegrina.

Researcher at the University of Exeter Alexander Sanchez He has been studying and denouncing light pollution for years. His latest work shows that instead of diminishing, the light projected by humans into the sky is increasing. “Across the planet, the minimum nighttime brightness has increased by 49% since 1992,” Sanchez recalls. lower limit because “the satellites we use to measure are blind to blue light,” he adds. It is in this range of the spectrum that the vast majority of LEDs driving the transition to this technology operate. Indeed, in another work, using data from the International Space Station, which has instruments that record different spectra of light, they saw an “11% increase in light pollution in green and another 24.4% in blue” in 2020 compared to 2012. In Europe and the United States The blame would be on the increase in “opting for a blue LED light, rather than amber, which is more natural,” says Sanchez. Also, the improvement of living conditions in such giants as India and China has led to more light pollution.

There is also a source of pollution to consider: satellite. “They fill the sky with light at sunset and dusk, when it’s still night on Earth, but up there the sun shines on them,” says Sanchez. They act like mirrors, reflecting sunlight and illuminating everything around them. As this researcher recalls, “Elon Musk wants to put another 30,000 satellites into orbit.” Not even observatories relocated to the deserts of Chile or Namibia will be able to escape.

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