Light pollution puts world's top astronomy hub under pressure

Chile's Atacama Desert, home to some of the darkest skies on Earth, has long been regarded as one of the world's premier locations for astronomical research. But scientists warn that the steady spread of artificial light from nearby cities, mining operations and industrial developments is beginning to threaten one of the planet's last remaining havens for observing the universe.

Astronomers have relied on the Atacama's unique conditions for decades. Its high altitude, exceptionally dry climate and near-total absence of light pollution make it one of the few places on Earth capable of supporting the world's most advanced ground-based telescopes, as highlighted in an open letter written by several academics by the Max-Planck Society of Germany.

Among them is the European Southern Observatory's (ESO) Paranal Observatory, which houses the renowned Very Large Telescope (VLT) and will soon be joined by the Extremely Large Telescope (ELT), scheduled for completion in 2029, with its dome and primary structure expected to be finished by 2027.

The observatory has played a pivotal role in some of the most significant astronomical breakthroughs of the 21st century, including capturing the first direct image of an exoplanet and tracking stellar motions that confirmed the existence of the supermassive black hole at the center of the Milky Way.

Unlike urban areas, where the glow of millions of streetlights and buildings obscures much of the night sky, the Atacama's remote landscape allows stars and distant galaxies to remain strikingly visible. But that advantage is gradually eroding.

Each year, artificial illumination from surrounding population centers, industrial facilities and mining projects creeps closer to Paranal, threatening the pristine darkness on which modern astronomy depends.

The challenge facing Chile's observatories reflects a much broader global trend. As electric lighting has expanded across the world, around 80% of the global population now lives under light-polluted skies.

A recent study found that night skies became nearly 10% brighter on average each year between 2011 and 2022 due to artificial lighting. Researchers estimated that someone who could see roughly 250 stars at the beginning of that period would be able to distinguish only about 100 by its end.

Scientists say the consequences extend far beyond astronomy. Psychologists have suggested that the gradual disappearance of the stars may weaken people's connection to the natural world and negatively affect mental well-being. Ecologists, meanwhile, have shown that artificial light disrupts the biological rhythms of plants and animals by mimicking daylight, altering feeding, reproduction and migration patterns throughout entire ecosystems.

Growing evidence has prompted some researchers to argue that excessive artificial lighting should be treated as a form of environmental contamination on par with air and water pollution.

Astronomers first sounded the alarm more than five decades ago, when researchers in California warned that expanding urban lighting around San Francisco would eventually interfere with telescope observations. At the time, scientists concluded that a 10% increase in night-sky brightness above natural levels would significantly compromise ground-based astronomy.

By 2022, that threshold had already been exceeded at roughly two-thirds of the world's leading observatories.

"Astronomical observatories can be seen as the proverbial canary in a coal mine," the researchers behind the study warned. "If we are not able even to keep the canary alive, then we can forget being able to solve the problem of light pollution as a global environmental issue."

Their findings showed that Chile's Atacama Desert remains one of the few major astronomical sites that has not yet crossed that critical threshold — but scientists caution that without stronger protections, even one of Earth's darkest skies may not remain untouched for much longer.

By Nazrin Sadigova