If the astronomers’ calculations are correct, it means we’ve surpassed a sky brightness threshold for unimpeded astronomical observation set decades ago by the International Astronomical Union, an association of professional astronomers who, among other things, assign names to newly discovered celestial bodies.
“Since there are objects orbiting the Earth in all manner of orbital inclinations, really nowhere is safe from this,” said John Barentine, director of public policy of the International Dark-Sky Association and a co-author of the study, which was published in the Monthly Notices of the Royal Astronomical Society, a scientific journal.
One major area of concern is the rise of satellite mega-constellations, like SpaceX’s Starlink project, which has put more than 1,300 satellites in orbit since 2018 with plans to potentially launch tens of thousands more. Other companies, including Amazon and OneWeb, also have constellation plans of their own (Amazon CEO Jeff Bezos owns The Washington Post).
Those figures would represent a massive increase over the current number of operational satellites in orbit, which the Union of Concerned Scientists estimates to be more than 3,300. The devices are used in telecommunications, navigation, weather monitoring, space science and other areas.
Some of the newer satellites have left glowing streaks through telescope images and prompted enough outcry among astronomers that Starlink has taken steps to reduce their luminosity. But the latest versions are still too bright by “a factor of more than 2,” Barentine said, noting that there is “no clear commitment” from the other commercial satellite operators to adopt the same brightness limit as SpaceX.
But the new research digs into the possibility of astronomical disruption above and beyond individual satellites’ direct effects on images. Every additional orbital object also contributes to an increase in the total luminosity of the light sky, as sunlight reflects off its surface and scatters throughout the atmosphere. The effect is similar to ground-based light pollution from lamps and other nighttime light sources, which effectively wash out the visual contrast of the night sky, making fainter astronomy targets more difficult to see.
It’s also plausible that we could be hampering our ability to detect hazardous asteroids on a collision course with earth. “I think the answer is ‘we don’t know,’” Barentine said, “but the idea that we might miss an object on a collision course with Earth is concerning.”
Christopher Kyba, a light pollution expert at the German Research Center for Geosciences who was not involved in the research, called the results “really shocking” but cautioned that they still need to be confirmed by experimental data.
“The problem with the reflected light from objects humans put into space (if the authors are correct) is that there’s almost nowhere on Earth you could go to avoid it,” Kyba said. “So as more satellites are put into orbit, all of Earth’s countryside and wilderness areas will get brighter.”
“The night sky is a gift the cosmos gives to all of humanity, inspiring awe and wonder and drawing our thoughts to some of the greatest questions humanity has ever asked in trying to understand the universe,” Barentine said. But, he added, “it’s already under assault in many parts of the world from terrestrial light pollution, and the contribution of diffuse light from satellites and space debris potentially robs us of something that is rightly the shared heritage of all people.”