Image credit: ESO/P. Horálek

The European Southern Observatory (ESO) and other astronomy groups are petitioning the United Nations to address the impact of satellites on dark and quiet skies.

An international collaboration involving ESO has submitted a paper to the United Nations Committee on Peaceful Uses of Outer Space (COPUOS) proposing a new “Expert Group” to protect dark and quiet skies.

The call for a new Expert Group is to push forward on monitoring the impact of satellites on astronomy and seeks inputs from global stakeholders to make recommendations to help mitigate their sky pollution concerns.

Dark sky reserves and radio quiet zones 

“The proliferation of satellites launched into orbit around the Earth has improved our ability to communicate globally instantaneously; however, there are concerns about the impact these technologies have on astronomical observations and the preservation of dark and quiet skies,” explains an ESO statement.

Starlink constellation pass overhead near Carson National Forest, New Mexico, photographed soon after launch.  
SpaceX Starlink Satellites over Carson National Forest, New Mexico, photographed soon after launch.
Credit: Mike Lewinsky/Creative Commons Attribution 2.0

The statement flags the fact that there are over 8,000 active and defunct satellites orbiting the Earth and this number will continue to grow. As many as 100,000 satellites could be launched in the coming decade. These new satellites are encroaching on the few remaining dark sky reserves and radio quiet zones.

Credit: SpaceX/StarLink

“Astronomers have already begun to notice the effects of the dramatic increases in space traffic. Even from remote locations — specifically chosen to isolate telescopes from unwanted light pollution — satellites interfere with optical and infrared observations,” the ESO statement adds. “These satellites also transmit and receive radio signals which is especially concerning for radio telescopes, such as the highly sensitive Atacama Large Millimeter/submillimeter Array of which ESO is a partner.”

Mitigation steps

The ESO statement notes that some companies have made efforts to mitigate these effects, such as use of less-reflective material in satellite construction or changing the orientation of satellites in space.

An image of the NGC 5353/4 galaxy group made with a telescope at Lowell Observatory in Arizona, USA on the night of Saturday 25 May 2019. The diagonal lines running across the image are trails of reflected light left by more than 25 of 60 Starlink satellites as they passed through the telescope’s field of view. Although this image serves as an illustration of the impact of reflections from satellite constellations, please note that the density of these satellites is significantly higher in the days after launch (as seen here) and also that the satellites will diminish in brightness as they reach their final orbital altitude.
Credit: Victoria Girgis/Lowell Observatory

A proactive step would have companies provide astronomers with higher accuracy information about the location of satellites so that observatories can take this into account to decide when and where to point their telescopes.

“While these potential solutions show promise, they will require a coordinated effort between satellite industry, governments, and astronomers,” the ESO statement continues. “A cooperative approach involving all stakeholders is an effective way to reach a satisfactory balance between the need for the evolution of the low-Earth orbit space economy and the need protect the science of astronomy and the pristine visibility of the night sky.”

Cascade effect

Andrew Williams, co-lead of the policy hub of the International Astronomical Union’s (IAU) Center for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference, stated that there is a cascade effect from the discussions at COPUOS that can influence governments and companies to act.

Nineteen Atacama Large Millimeter/submillimeter Array (ALMA) antennas on the Chajnantor Plateau in Chile.
Image credit: ALMA (ESO/NAOJ/NRAO)/W. Garnier (ALMA)


“From the substantial number of countries from all regions of the globe that voiced support for our proposal, we are hopeful we can find a way forward at the main session of the committee,” Williams says.

The mission of the IAU Center is to coordinate efforts and unify voices across the global astronomical community with regard to the protection of the dark and quiet sky from satellite constellation interference.

A “Conference Room Paper on the Protection of Dark and Quiet Skies for science and society” has been endorsed by Chile, Spain, Slovakia, Bulgaria, Dominican Republic, Peru, South Africa, in addition to ESO, the International Astronomical Union (IAU) and the Square Kilometer Array Observatory (SKAO).

That paper is available at:

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