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How satellites add significant light pollution to the night skies

A new study looks at the overall impact of space objects—functioning satellites and space debris—on the night sky

This slow shutter speed image shows a trail of a group of SpaceX's Starlink satellites passing over Uruguay as seen from the countryside some 185 km north of Montevideo near Capilla del Sauce, Florida Department, on February 7, 2021. (Photo by Mariana SUAREZ / AFP) (AFP)

Scientists believe that artificial objects in orbit around the Earth are brightening night skies on our planet significantly more than previously understood.

According to latest research, which has been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society: Letters, the number of objects orbiting Earth could ramp up the overall brightness of the night sky by more than 10 per cent above natural light levels across a large part of the planet. This scenario would exceed a threshold that astronomers set over 40 years ago for considering a location “light polluted”.

“Our primary motivation was to estimate the potential contribution to night sky brightness from external sources, such as space objects in Earth's orbit,” Miroslav Kocifaj of the Slovak Academy of Sciences and Comenius University in Slovakia, who led the study, said in an official release from the Royal Astronomical Society. “We expected the sky brightness increase would be marginal, if any, but our first theoretical estimates have proved extremely surprising and thus encouraged us to report our results promptly,” Kocifaj added.

This research is the first to assess the overall impact of space objects on the night sky rather than the effect of individual satellites and space debris affecting astronomers' images of the night skies. The team of researchers, based at institutions in Slovakia, Spain and the US, modelled the space objects' contribution to the overall brightness of the night sky, using the known distributions of the sizes and brightnesses of the objects as inputs to the model, the release explains.

A long exposure shows a streak across the sky from the launch of a Falcon 9 rocket and 60 Starlink satellites from Launch Complex 40 at Cape Canaveral Space Force Station, early Wednesday, March 24, 2021, in Florida.
A long exposure shows a streak across the sky from the launch of a Falcon 9 rocket and 60 Starlink satellites from Launch Complex 40 at Cape Canaveral Space Force Station, early Wednesday, March 24, 2021, in Florida. (AP)

For the study, researchers included both functioning satellites as well as assorted debris such as spent rocket stages. While telescopes and sensitive cameras often resolve space objects as discrete points of light, low-resolution detectors of light such as the human eye are able to see only the combined effect of many such objects. “The effect is an overall increase in the diffuse brightness of the night sky, potentially obscuring sights such as the glowing clouds of stars in the Milky Way, as seen away from the light pollution of cities,” the release adds.

Also read: The race to clean up outer space

John Barentine, director of public policy for the International Dark-Sky Association and co-author of the study, says unlike ground-based light pollution, this kind of artificial light in the night sky can be seen across a large part of the Earth's surface. “Astronomers build observatories far from city lights to seek dark skies, but this form of light pollution has a much larger geographical reach,” he said in the release.

In recent years, astronomers have expressed unease about the growing number of objects orbiting the planet. This has only been amplified by the large fleets of communications satellites, known informally as ‘mega-constellations’, as the arrival of this technology increases the probability of collisions among satellites or between satellites and other objects, generating further debris. Recent reports sponsored by the US National Science Foundation and the United Nations Office for Outer Space Affairs identified mega-constellations as a threat to the continued utility of astronomy facilities on the ground and in low-Earth orbit, the release adds.

According to the release, researchers hope that this study will change the nature of the ongoing dialog between satellite operators and astronomers concerning how best to manage the orbital space around the Earth.

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