Atacama desert skies in Chile face light-pollution pressure

The Atacama Desert in Chile has long drawn astronomers because the combination of dry climate, high altitude and — crucially — limited interference from urban light supports some of the clearest views of the universe. In the Paranal area, where multiple observatories operate in a high-altitude corridor often referred to as “Photon Valley,” researchers say maintaining darkness is not just a scenic preference: even small amounts of outside light and other environmental disturbances can undermine observation quality.

Chiara Mazzucchelli, president of the Chilean Astronomical Society, said the Atacama has “more than 300 clear nights per year,” adding that the setting means “no clouds and no rain.” The AP visit described the effect on arrival: after eyes adjust to the dark, stars, planets and entire constellations come into view, with even galaxies visible to the naked eye in conditions the article described as exceptional.

Those conditions have enabled major, long-term projects, including the Extremely Large Telescope, or ELT, a $1.5 billion effort by the European Southern Observatory scheduled for completion in 2030. The article said the ELT will use 798 mirrors and a light-gathering area of nearly 1,000 square meters (a quarter of an acre), and that it is designed to be 20 times more powerful than today’s leading telescopes and 15 times sharper than NASA’s Hubble Space Telescope. ESO astronomer Lucas Bordone said in the article that with the ELT, researchers “we should be able to see Earth-like planets in what we call the habitable zone.”

But the article also described how the “darkest skies” that enable those instruments are under pressure as development expands across northern Chile. It cited changing conditions driven by urban sprawl, industrial development, and the arrival of mining and wind farms, all of which increase the challenge of preserving darkness in the region where Paranal sits. Specialists at Paranal are described as living with lighting restrictions, with windows covered and common areas kept dark so that even faint light can interfere less with telescopes’ work.

Last year, the concerns intensified after an energy firm proposed a green power complex just kilometers from Paranal. The article said that proposal would have been managed by ESO and that the site is also expected to host the future ELT. Although the AP story said the energy project was canceled in January following a massive appeal from astronomers, physicists and Nobel laureates, it also said the episode exposed “deep concerns” that existing sky-preservation laws are lax, outdated and unclear.

Since the cancellation, multiple environmental regulations have come under review in Chile, including guidance from the science ministry aimed at protected astronomical zones. Daniela González, director of the Cielos de Chile Foundation, said in the article: “We are working to ensure the new criteria are strict enough to guarantee that there will be no impact on astronomical areas.” She described the nonprofit as focused on protecting the quality of Chile’s night skies.

The AP report said astronomers and researchers remain worried not only about light pollution but also about other physical impacts that development can bring, including micro-vibrations and dust, along with increased atmospheric turbulence. It quoted Itziar de Gregorio-Monsalvo, ESO’s representative in Chile, as saying that ESO’s telescopes in particular are among the most powerful astronomical facilities on the planet. It also quoted de Gregorio-Monsalvo saying that putting the ELT close to a city would have consequences regardless of the telescope’s scale, noting that “If you place the ELT next to a city, it doesn’t matter that its diameter is 40 meters long. It’s just the same as having a tiny telescope.”

Researchers also pointed to past examples of environmental contamination affecting observatory operations. Eduardo Unda-Sanzana, director of the Astronomy Center at the University of Antofagasta, recalled that 70 years ago was not the first time Chile’s astronomy faced such risks, saying the first international heliophysics observatory in Chile — a solar station operated by the U.S. Smithsonian Institution in the early 20th century — shut down operations in 1955 after environmental pollution tied to mining expansion in the area. Unda-Sanzana warned that without updated regulations, similar problems could recur, telling the AP that despite media attention in 2025, the situation remained much the same as it had been the year before.

Finally, the article described the long odds and hard conditions that underpin day-to-day work at Paranal, including reduced oxygen levels at altitudes above 3,000 meters (10,000 feet) and temperature swings from scorching days to relentlessly cold nights. It said the Atacama draws thousands of researchers annually, and it quoted Julia Bodensteiner, an assistant professor at the University of Amsterdam, saying the chances of being selected as a visiting astronomer at Paranal are “just 20% to 30%.” Against that backdrop, scientists argue that protecting the darkness that supports the next generation of telescopes requires clear rules that hold up when new development proposals emerge.