ESO and international partners petition UN for the protection of the Earth’s dark and quiet skies

7 februari 2022

An international collaboration involving ESO has submitted a new paper to the United Nations Committee on Peaceful Uses of Outer Space (COPUOS) seeking better protections for the Earth’s dark and quiet skies. The paper was accepted for discussion today at the ongoing session of the COPUOS Scientific and Technical Subcommittee, marking the first time the dark and quiet skies have ever been tabled as a formal agenda item by the United Nations. The paper, which has been endorsed by Chile, Spain and Slovakia, encourages the international community to protect global astronomical observing capabilities from disruptive and harmful artificial interference.  

The night sky offers a rich tapestry of stars to the fortunate viewer, but over the last few decades, its quality has been diminished as a result of encroaching ground-based light pollution. A new threat is now emerging: the large number of satellites being introduced into low Earth orbits. As many as 100 000 satellites could be placed into these orbits in the coming decade. While important for global communications networks, these satellites can disrupt astronomy because of the sheer number of them, their brightness in the sky, and their ubiquitous radio emissions. In particular, they can affect measurements which require twilight observation, such as searches for Earth-threatening asteroids.  

By the 2030s more than 5000 satellites could potentially be detectable above a typical mid-latitude observatory at any given moment. This will be noticeable in all wide-field images obtained at twilight except those taken by the smallest optical telescopes. Large constellations of satellites also pose a challenge to radio astronomy. The sheer number of new satellites will result in thousands of additional radio transmitters, affecting the measurements made by highly sensitive radio telescopes. There is a clear need for better global coordination, policies and laws for dark skies protection, but also for radio-quiet skies. 

The paper presented to the COPUOS subcommittee outlines four main actions to combat the impact of satellites on astronomical observatories: recognising that ground and space-based astronomical research constitute an instrumental part of space exploration; raising the attention of governments to the harm created by the uncontrolled expansion of artificial light at night; supporting the adoption of the set of voluntary best practice guidelines for satellite constellation operators; ensuring that the “Impact of satellite constellations on astronomical facilities” is included in the agenda of the Scientific and Technical Subcommittee until the issue is satisfactorily resolved. 

The paper was co-signed by ESO, the International Astronomical Union (IAU) and the Square Kilometre Array Observatory (SKAO), and will be discussed on Monday 14 February as part of the 59th session of the COPUOUS Scientific and Technical Subcommittee. This will give international delegates the chance to digest, discuss, and outline potential future actions relating to the protection of the dark and quiet night skies. The discussion is a key step in engaging international lawmakers in global protective measures for astronomy. 

An international approach is vital for protecting the dark and quiet skies. Collaborative efforts are required from governments, industry, astronomers. Even private citizens, whose access to the sky should be preserved for important cultural and heritage reasons, have a part to play in the campaign. ESO, a permanent observer at COPUOS, has consistently advocated for policy action surrounding dark and quiet skies protection.  

It is critical for ESO to be a member of COPUOS because that’s where we are able to advocate for astronomy to policy makers,” says ESO External Relations Officer Andrew Williams, who represents ESO at COPUOS. “With the inclusion of the dark and quiet skies as an agenda item, we have brought this issue to prominence, ensuring governments worldwide are listening to the needs of the astronomy community.” 

The recommendations outlined in the paper draw on a recent report produced by the Dark and Quiet Skies Working Group, an international collaboration led by the IAU and involving ESO scientists and policy experts. The report looks at how policy measures can be implemented to reduce the impact of satellite constellations on astronomy.  

We hope that the COPUOS Scientific and Technical Subcommittee adopts the four proposed actions,” says ESO Director General Xavier Barcons. “This will take us closer to the legislative, global change required to preserve the legacy of our night skies.”



Andrew Williams 
ESO External Relations Officer 
Garching bei München, Germany 
Tel: +49 89 320 062 78 

Bárbara Ferreira 
ESO Media Manager 
Garching bei München, Germany 
Tel: +49 89 3200 6670 

Over de Mededeling



Colour before the dark
Colour before the dark