Not only do the cities on Earth contribute to light pollution around the planet but the light pollution created by the high number of satellites orbiting Earth poses an "unprecedented global threat to nature," astronomers have warned.

The number of satellites in low Earth orbit has more than doubled since 2019 when United States company SpaceX launched the first "mega-constellation," which comprises thousands of satellites. In addition, an armada of new internet constellations will launch soon, adding thousands more satellites to the already congested area fewer than 2,000 kilometers (1,250 miles) above Earth.

Each new satellite increases the risk of smashing into another object orbiting Earth, creating yet more debris. This can create a chain reaction in which cascading collisions create ever smaller debris fragments, further adding to the cloud of "space junk" reflecting light to Earth.

In a series of papers published in the journal Nature Astronomy, astronomers warned that this increasing light pollution threatens the future of their profession. In one report, researchers said that for the first time, they had measured how much a brighter night sky would financially and scientifically affect the work of a major observatory.

Modeling suggested that for the Vera Rubin Observatory, a giant telescope currently under construction in Chile, the darkest part of the night sky will become 7.5% brighter over the next decade. That would reduce the number of stars the observatory can see by around 7.5%, study co-author John Barentine told Agence France-Presse (AFP).

That would add nearly a year to the observatory's survey, costing around $21.8 million, said Barentine of Dark Sky Consulting, a firm based in the U.S. state of Arizona. He added that another cost of a brighter sky is impossible to calculate: the celestial events that humanity will never observe.

And the increase in light pollution could be even worse than thought. Another Nature study used extensive modeling to suggest that current light pollution measurements significantly underestimate the phenomenon.

'Stop this attack'

The researchers warned that the brightening of the night sky would not just affect professional astronomers and significant observatories. Aparna Venkatesan, a University of San Francisco astronomer, said it also threatened "our ancient relationship with the night sky."

"Space is our shared heritage and ancestor – connecting us through science, storytelling, art, origin stories, and cultural traditions – and it is now at risk," she said in a Nature comment piece.

A group of astronomers from Spain, Portugal, and Italy called for scientists to "stop this attack" on a natural night.

"The loss of the natural aspect of a pristine night sky for all the world, even on the summit of K2 or on the shore of Lake Titicaca or Easter Island, is an unprecedented global threat to nature and cultural heritage," the astronomers said in a Nature comment piece. "If not stopped, this craziness will become worse and worse."

The astronomers called for drastically limiting mega-constellations, adding that "we must not reject the possibility of banning them." However, they said it was "naive to hope that the skyrocketing space economy will limit itself, if not forced to do so," given the economic interests at stake.