Astronomers from all over the world are mobilizing to keep our light-polluting civilization from creeping into what they have for years deemed sacred territory. 

The proverbial battle ground is the Atacama Desert in Chile, a high-land plateau in the foothills of the South American Andes. Scattered across its arid peaks at altitudes of over 6,500 feet (2,000 meters) are some of the world’s most powerful astronomical observatories. In addition to its remoteness, astronomers have earmarked Atacama for their most challenging observations because of the clarity through the atmosphere above it. Shielded by the more than 20,000-foot (6,000 m) summits of the magnificent Andes range, the air above Atacama is the driest on the planet. Clouds are scarce, rain is precious.

For the observatories it means more than 300 nights a year of perfectly unobstructed views of the most distant universe. A proposed industrial park threatens this hallowed night sky.

The U.S. energy company AES Energy is now planning to build a major complex in the area to produce green hydrogen using wind and solar power. Astronomers are concerned that light pollution from the 3,021-hectare development will increase the brightness of the night sky above so much that up to 30% of the faintest stars and galaxies could disappear from the telescopes’ view. 

Among the Atacama telescopes, those enjoying the most unspoiled cosmic views are located on Mount Paranal, an 8,645-foot-high (2,635-m) peak some 745 miles (1,200 kilometers) north of Chile’s capital Santiago. Since the 1990s, Mount Paranal has been home to the European Southern Observatory’s (ESO) Very Large Telescope (VLT), an assembly of four 28-foot-wide (8.5 m) telescopes that act as one super-powerful star-observing machine.

Only 12 miles away (20 kilometers), on the top of the neighboring Mount Armazones, the even more potent Extremely Large Telescope (ELT) is being built by ESO, a nearly 125-foot-wide (38 m) single-mirror super telescope, the largest in the world to observe the sky in visible light. 

It's not just the future of ESO’s Paranal and Armazones observatories that is at stake. Astronomical organizations from all over the world that run telescopes in Chile are watching the situation with concern that its approval may usher in the beginning of the end of the world’s most scientifically valuable night sky.

“If you allow the precedents, if you allow one company to do that, that opens the door for any company to do that to any observatory in Chile,” an astronomer familiar with the situation who didn’t wish to be named, told Supercluster.

For example, the U.S. National Optical-Infrared Astronomy Research Laboratory (NOIR Lab) operates several observatories in the Atacama Desert including the 27-foot-wide Gemini South telescope and the unique Vera Rubin Observatory, which is expected to come online later this year. Fitted with the world’s largest camera, the $571 million Rubin will survey the sky, completing a full-sky map every three nights. This vast data set will allow astronomers to chart the structure of the universe in unprecedented detail and observe transient phenomena across the entire sky, such as supernova explosions that destroy large stars at the end of their lives. Any increase of the artificial glow of the night sky could hide some of the celestial objects from Rubin’s view.

Astronomy has been running away from civilization for more than 100 years. The arrival of electrical lights, which began replacing the much less luminous gas streetlamps in the early 20th century, paired with the rapid expansion of urban populations, pushed observatories further out into the wilderness.

In the 1920s, the legendary U.S. astronomer Edwin Hubble made his ground-breaking observations of the Andromeda nebula from the Mount Wilson Observatory located only about 16 miles (25 kilometers) from the center of Los Angeles. With a population of over half a million, the burgeoning Los Angeles was at that time the fifth largest city in the U.S. Its city lights, however, were already hindering the Mount Wilson’s Observatory’s potential, Tim Thompson, Science Director at the Mount Wilson Institute, told Supercluster.

“It was already in the 1920s when [Caltech astronomer] Fritz Zwicky advised against putting the planned 200-inch Hale Telescope on Mount Wilson due to the growth of Los Angeles,” Thompson. “That’s one big reason why it is on Palomar Mountain.”

Today, the Mount Wilson Observatory is the most light-polluted among 28 major astronomical research locations in the western world. A 2023 study led by Italian light pollution expert Fabio Falchi found that the artificial glow of the nighttime sky over Mount Wilson has increased by a staggering 1350 percent compared to natural levels. 

The beleaguered Mount Wilson Observatory had to reinvent itself to remain relevant in the 21st century, Thompson admitted. Observations in visible light, which enabled Edwin Hubble to prove that the Universe extends beyond the Milky Way galaxy, are no longer feasible on the level needed for cutting-edge science. 

“Light pollution, however, has no real impact on the sky at near infrared wavelengths,” Thompson said. “From Mount Wilson Observatory, wavelengths of 1 to 2.5 microns can be readily observed, which is the wavelength range in which our CHARA Array does its observing.”

The Palomar Mountain, chosen by Zwicky as the preferred site for, at that time, the world’s new largest telescope, is no longer free from light pollution either. The observatory, located some 120 miles (200 km) south from Los Angeles and 70 miles (110 km) northeast from San Diego, has seen an 170 percent increase in nighttime light levels compared to the natural state. 

Among the 28 observatories included in the 2023 study by Fabio Falchi, the telescopes on Chile’s Mount Paranal were found to benefit from the lowest levels of artificial light pollution. The background glow above the ESO observatory has, according to the paper, increased merely by  1 percent compared to natural levels. That makes Paranal one of only a handful astronomical locations around the globe where light pollution has not yet increased the nighttime glow of the sky by more than 10 percent. According to the International Astronomical Union a 10 percent increase in night sky brightness compared to natural levels is a threshold behind which astronomy begins to suffer. 

The AES Energy green hydrogen park could tip the Paranal and Armazones observatories over that limit, Xavier Barcons, the Director General of ESO, told Supercluster. 

“The brightness of the sky is going to increase by 1 to 10 percent only from this project,” Barcons said. “And let’s not forget that there is an aim to create a hub, meaning that other projects may get attracted into the area and the effects will pile up.”

AES Energy, on the other hand, thinks the facility will have only a minor impact. 

“The proposed project's light impact has been evaluated considering the specific locations of nearby astronomical activities,” AES Energy’s spokesperson Stephanie Cathcart told Supercluster in an email. “Calculations confirm that the maximum increase over the natural sky brightness is only 0.27% at Cerro Paranal and 0.09% at Cerro Armazones, both well below the permitted limit, ensuring the protection of these astronomical areas.”

Fabio Felchi is concerned about the situation, although he admits he has not yet evaluated the impact of the green hydrogen project on Paranal in his light pollution models. In his previous studies of light pollution in Chile, he and his colleagues found that the trans-Chilean Ruta 5 highway creates measurable light pollution at the Las Campanas observatory over 18 miles (30 km) away.

“There are far fewer light installations along Ruta 5 than we expect at this new green hydrogen project,” Falchi told Supercluster. “I believe it’s important to relocate this project further away from the Paranal Observatory.”

While Fritz Zwicky could relocate the largest optical telescope of his era to a more remote, darker location, ESO astronomers have no alternatives for their VLT and ELT machines.

“All the farther away places that astronomers have searched for decades to build their telescopes are now at least a bit light polluted,” Falchi said. “We have arrived at a limit. We cannot escape anymore from civilization.”

He stresses that it’s not just astronomy that suffers from the omnipresent nighttime glow, so do human circadian rhythms and the well-being of animals and plants that evolved over millions of years to rest in perfect darkness. He proposes that light pollution should be regulated just like any harmful pollutant that humankind has ever created.

Connie Walker, an astronomer and light pollution expert at NOIR Lab, tries to remain optimistic, hoping that astronomy and civilization might find a way to coexist. The biggest blow to astronomy worldwide was the advent of light-emitting diodes, or LEDs, which began replacing incandescent light bulbs in the early 2010. Cheaper, less power-hungry, brighter and glowing in the bluer part of the spectrum, LEDs took the world by storm, accelerating the spread of light pollution. Since their arrival, light pollution levels worldwide have been increasing by a staggering 9.6 percent per year, according to another 2023 research paper. But new technologies are becoming available that could reverse at least part of that damage. 

“New lights are being developed that are coated in phosphor and produce amber colored light that only shine in a limited part of the spectrum,” Walker told Supercluster.

Orange light doesn’t scatter as much as white or blue light does, causing less overall sky glow. As it only occupies a limited portion of the visible light spectrum, it doesn’t interfere with most astronomical observations. 

In humankind’s history, however, the battle between pure utility and the preservation of our natural world has never been an easy one. The global astronomical community is up in arms, lobbying for regulations that would prevent unhindered nighttime lighting from taking over the entire planet. The battle over the Paranal skies marks an important milestone in this struggle.