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New Study Finds Satellites Contribute Significant Light Pollution To Night Skies

Bright trails of light from SpaceX Starlink satellites are seen across this image of the night sky made in Berlin, Germany, on 20th April 2020. Photo by Andreas Möller (CC-by-sa 4.0)

Scientists reported new research results today suggesting that artificial objects in orbit around the Earth are brightening night skies on our planet more than previously understood.

The research, accepted for publication in Monthly Notices of the Royal Astronomical Society Letters, finds that objects orbiting Earth elevate the brightness of the night sky by at least 10 percent over natural light levels, exceeding 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,” said Dr. Miroslav Kocifaj of the Slovak Academy of Sciences and Comenius University in Slovakia, who led the study.

“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.”

A new approach to assessing impact

The work is the first to consider 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 sky. 

The team of researchers, based at institutions in Slovakia, Spain and the U.S., modeled the space objects’ contribution to the overall brightness of the night sky, using as inputs to the model the known distributions of the sizes and brightnesses of the objects. These include 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 see only the combined effect of many such objects. The effect is an overall increase in the diffuse brightness of the night sky, such as the glowing clouds of stars in the Milky Way as seen away from the light pollution of cities.

“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,” explained John Barentine, IDA’s Director of Public Policy and a study co-author.

“Astronomers build observatories far from city lights to seek dark skies, but this form of light pollution has a much larger geographic reach.” 

Concerns grow with the launch of ‘mega-constellations’

Astronomers have expressed unease in recent years about the growing number of objects orbiting the planet, particularly large fleets of communications satellites known informally as ‘mega-constellations.’ 

In addition to crowding the night sky with more moving sources of artificial light, the arrival of this technology increases the probability of collisions among satellites or between satellites and other objects, generating further debris.

A summary of all objects in Earth orbit officially cataloged by the U.S. Space Surveillance Network as of 2019. Graphic by the U.S. National Aeronautics and Space Administration Orbital Debris Program Office.

Recent reports sponsored by the U.S. National Science Foundation and the United Nations Office for Outer Space Affairs identified mega-constellations as a threat to the continued utility of billions of dollars’ worth of astronomy facilities on the ground and in low-Earth orbit.

The new science results published today imply a further brightening of the night sky proportional to the number of new satellites launched and their optical characteristics on orbit. Satellite operators like SpaceX have recently worked to lower the brightness of their spacecraft through design changes.

Despite these mitigating efforts, the collective effect of a sharp increase in orbiting objects stands to change the experience of the night sky for many.

The researchers hope that their work will change the nature of the ongoing dialog between satellite operators and astronomers concerning how best to manage the orbital space around the Earth.

“Our results imply that many more people than just astronomers stand to lose access to pristine night skies,” Barentine said. “This paper may really change the nature of that conversation.”