Dark Embrace
In the Chilean desert, stargazers want to dim the lights on a mining boom.
When Eduardo Unda-Sanzana arrived in Chile’s Atacama Desert to teach astronomy, the darkness was disorienting. The remote location of the small observatory at Catholic University of the North made it an ideal vantage point from which to study variable stars and exoplanets. But without the telltale nighttime aura, Unda-Sanzana couldn’t make out where the nearest city stood.
That was in 2005. Today, as director of the Ckoirama Observatory, also in the Atacama, Unda-Sanzana has no trouble discerning the location of Antofagasta, a city on the Pacific Coast that’s logged a more than 50% population increase in the past two decades.
Cities aren’t the only source of light pollution in the Atacama. Mines have also become a visible contributor. As extraction of copper and lithium ramps up to meet soaring global demand for minerals critical to the clean energy transition, Unda-Sanzana and other astronomers working in the area worry that the Chilean desert’s status as the “eyes of the world” could be in jeopardy.
“We’re all concerned that the current situation does not become worse than it is,” Unda-Sanzana, who is also a professor at the University of Antofagasta, says. “You never know when they are going to announce a new stage of a large mining facility.”
A mountainous region covering about 40,000 square miles and one of the most arid places on the planet, the Atacama has been luring astronomers for decades, thanks in part to generous tax breaks from the Chilean government. The area’s exceptionally clear skies have revealed profound discoveries, including potentially hazardous asteroids drifting close to Earth and evidence that the universe’s expansion is accelerating.
Two multibillion-dollar projects under construction—the Extremely Large Telescope and the Giant Magellan Telescope—may help establish whether there’s life beyond our solar system. By the end of the decade, Chile will host more than half of the world’s observation capacity, says Daniela González, executive director of the Skies of Chile Foundation, a nonprofit that advocates limiting light pollution.
But as science gazes up, industry is drilling down. Chile is the world’s top producer of copper and No. 2 in lithium. The vast majority of this mineral wealth is buried in the Atacama.
Many of the mining installations run 24/7 and use LED lighting to operate at night—an energy-efficient choice, but particularly harmful from a light pollution standpoint because the unfiltered emissions of commonly used cool-white LEDs, with their shorter blue wavelengths, scatter more than amber and yellow lighting.
That’s affecting skies shared with nearby observatories. Ckoirama, where Unda-Sanzana works, is less than 10 kilometers (6.2 miles) from Aguas Blancas, an iodine mine. Escondida, the largest copper mine in the world, and Zaldívar, another major copper deposit, are almost 100km away but still generate as much light pollution as a small city.
While actual cities are bigger emitters, the proximity of these facilities—particularly in the northern part of the desert—can be a problem for observatories, says Igor Valdebenito, head of the Chilean Ministry of the Environment’s noise, light and odor department. “Scientists are contemplating the composition of the universe,” he says. “In that type of endeavor, they are very sensitive to the glow of humans.”
As the night brightens and so-called halos of light pollution rise closer to the celestial zenith, it’s harder for astronomers to spot distant objects because of the weakening contrast with the sky.
Guillermo Blanc, an astronomer and researcher at Carnegie Institution for Science based at the Las Campanas Observatory and president of the Skies of Chile Foundation, likens the effect to hearing someone speak while there’s heavy noise in the background: “You’re trying to listen, but the louder it is, the harder it is to hear a faint sound. It’s the same with visuals.”
For now, the problem hasn’t stopped scientists from doing their work. At most observatories in the Atacama, the skies are still less than 5% brighter than natural conditions, with sites in the urbanized southern part of the desert, such as the Cerro Tololo Inter-American Observatory, more affected than those in the north. That’s far below light pollution levels at observatories in places such as Southern California, where explosive urban growth in the 20th century bleached out skies, rendering several major telescopes less effective.
Researchers have pressed the Chilean government to take a proactive stance. The South American nation first regulated light pollution in 1998 by setting an upper limit on blue light in outdoor illumination in the Atacama and surrounding regions. Two decades later, Unda-Sanzana and other stakeholders started lobbying lawmakers to set more stringent standards. In 2023 the Ministry of the Environment officially expanded the outdoor lighting norm so it applies to the entire country, joining a handful of European countries that have adopted similar measures.
In addition, the government formally recognized special “astronomical areas” where even tighter restrictions apply. To be approved by regulators, new developments will have to submit an environmental analysis with plans to mitigate lighting’s impacts. The changes will come into full effect in October, though there’ll be a compliance window of two to five years; Blanc says the policies should effectively mean more amber-colored lights.
While mining isn’t the main target of the rule change, its threat could grow. The Chilean government estimates a $66 billion pipeline of projects over the next decade. The mining industry supports about 300,000 jobs in Chile and accounts for 12% of gross domestic product.
Chile’s Mining Council, a trade group, declined to comment on the effects the stricter light rules would have on its members. Another industry association, Sonami, also declined to comment. None of the mining companies contacted directly by Bloomberg Businessweek provided comment on the measures or plans for reducing light pollution.
Astronomers hope the mines will comply with the new lighting standards. Cities, with so many different sources of illumination, will likely be the bigger challenge. While it’s unlikely that the Atacama’s skies will return to the pitch-black of 20 years ago, Unda-Sanzana is cautiously optimistic that light pollution levels will at least stabilize.
“If you’re trying to attract new observatories, you need to give them the confidence to invest in the region, that things are not going to change for years to come,” says the Chilean astronomer. “We are trying to send a strong signal that we are invested in protecting the sky.”