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Satellites and Space Junk Threaten the Dark Night Skies and Astronomy

For centuries, humans have looked up at the night sky in awe, but in recent years, the night sky has been changing. With the rise of ground-based light pollution and the increasing numbers of satellites and space debris in orbit around Earth, the night sky is becoming brighter. This phenomenon may make it harder for astronomers to do research and for people to view an unpolluted night sky.

The number of functional satellites in orbit has more than doubled since 2019, and by the end of this decade, there may be 100,000 satellites in orbit around Earth. These satellites reflect sunlight towards the night side of Earth, making the night sky appear less dark. This, in turn, impacts astronomy by appearing as moving points of light and increasing diffuse night sky brightness.

In a recent study, researchers presented calculations of the aggregate effects of satellites and space debris in low-Earth orbit on major ground-based astronomy research facilities. The study found that reflected light from objects in low-Earth orbit will likely increase the diffuse background brightness for large-scale surveys of the night sky by at least 7.5% compared to an unpolluted sky. This would diminish the efficiency of the survey by 7.5% as well, adding some US$21.8 million to the total project cost.

Brighter night skies mean longer exposures through telescopes are needed to see distant objects in the cosmos. This will mean that less science will be accomplished, and there will be increased competition for telescope access. In addition, brighter night skies will reduce the detection limits of sky surveys, resulting in missed research opportunities.

Increases in diffuse night sky brightness will also change how we see the night sky with the unaided eye. An increase in satellites and space debris will create an even greater increase in the apparent brightness of the night sky, making it increasingly difficult to see fainter stars and the Milky Way.

The projected increase in night sky brightness will have profound consequences for professional astronomy and for anyone who wishes to view an unpolluted night sky. This transformation of the night sky is without historical precedent and with limited oversight. As humans continue to launch more and more satellites, it is important to consider the impact on the natural environment, including the night sky.

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