At the 46th COSPAR Scientific Assembly, astronomers, space-industry executives, policymakers and legal experts confronted a problem that is rapidly moving from specialist concern to global debate: how can humanity continue expanding satellite services without turning the night sky brighter and the radio spectrum noisier? During a session chaired by Marco Tavani, the panel examined the growing pressure that satellite constellations place on both optical and radio astronomy, while stressing that protecting the sky is essential not only for science but also for culture, education and the environment.
The phrase “dark and quiet skies” describes two connected but technically distinct goals. A dark sky is one with minimal artificial light, allowing optical telescopes to detect faint stars, galaxies, exoplanets and transient events. A quiet sky is one in which radio-frequency interference is sufficiently controlled for radio observatories to measure extremely weak natural signals. These signals can be millions or billions of times weaker than transmissions produced by human technology, making even emissions that seem insignificant to everyday communications potentially disruptive to astronomical research.
Satellites can interfere with optical observations in several ways. Their surfaces, solar panels and other components reflect sunlight toward Earth, creating bright streaks that cross long-exposure images. The problem is especially severe during twilight, when the ground may already be dark but satellites remain illuminated at high altitude. A single streak can contaminate an image, saturate pixels or obscure a transient object. Repeated trails can reduce the usable area of a telescope’s detector and complicate automated surveys designed to identify moving asteroids, exploding stars and other rapidly changing phenomena.
The impact is not limited to visible light. Modern astronomical instruments observe across a broad range of wavelengths, including infrared, where heat emitted by spacecraft and reflections from satellite surfaces can also affect observations. Large constellations create a continuously changing orbital environment, requiring observatories to predict satellite positions and adjust their schedules or telescope pointing. Such strategies can reduce some effects, but they cannot eliminate data loss, particularly for wide-field surveys that monitor huge portions of the sky at once.
Radio astronomy faces a different kind of threat. Satellites communicate through carefully assigned frequency bands, but radio telescopes often operate at frequencies close to, or even overlapping with, portions of the spectrum used by space-based systems. Interference may arise from authorised signals, unwanted emissions outside their allocated bands or electromagnetic radiation generated unintentionally by onboard electronics. Because radio observatories seek faint emissions from distant planets, molecular clouds, pulsars and the early Universe, even weak signals from nearby satellites can overwhelm the cosmic data researchers are trying to collect.
The panel highlighted the importance of distinguishing between technical progress and regulatory responsibility. The International Telecommunication Union establishes international rules for radio-frequency use, including the allocation and coordination of spectrum. Its work is central to limiting harmful interference, but spectrum regulation alone cannot address satellite brightness, orbital congestion or the broader cultural value of the night sky. The United Nations Committee on the Peaceful Uses of Outer Space will continue considering Dark and Quiet Skies as a dedicated agenda item over the next three years, creating a forum where scientific, environmental, legal and operational concerns can be addressed together.
The discussion also placed astronomical protection within the wider environmental debate surrounding near-Earth space. More satellites mean more opportunities for collisions, more complex traffic management and a greater risk of debris generation. Researchers are also investigating possible atmospheric effects associated with spacecraft launches and re-entry. Although these issues were not the main focus of the COSPAR session, speakers stressed that they are connected: decisions about satellite design, deployment, operation and disposal will influence both the sustainability of orbital activities and the quality of observations made from Earth.
Protecting the night sky matters beyond observatories. Natural cycles of light and darkness influence the behaviour, navigation and reproduction of many species, while artificial light pollution can disrupt ecosystems. For human societies, dark skies have shaped calendars, navigation, mythology, art and scientific discovery. The ability to see the Milky Way remains an accessible way for people to connect with science, yet it is disappearing from many populated regions. The rapid development of satellite networks has therefore intensified a conversation already underway about how much artificial illumination the planet can absorb before a shared natural heritage is permanently diminished.
This was the first dedicated Dark and Quiet Skies discussion at a COSPAR Scientific Assembly, and the strong interest demonstrated how quickly the issue is becoming a defining challenge for modern astronomy. The panel included representatives from COSPAR, the International Astronomical Union, the European Space Agency, the International Telecommunication Union, the Square Kilometre Array Observatory, industry and the Vatican Observatory. COSPAR plans to establish a dedicated Task Group to support existing initiatives and help develop practical solutions, including improved spacecraft design, coordinated observation strategies, better emission controls and international policy. The central message was clear: satellite technology can continue delivering vital services, but its future will depend on whether industry, governments and scientists can preserve humanity’s ability to see and hear the Universe.
Subject of Research: The effects of satellite constellations and space activities on optical and radio astronomy, including light pollution, radio-frequency interference, orbital sustainability and protection of the natural night sky.
Article Title: Dark and Quiet Skies: Astronomers Warn That Satellite Growth Could Change How Humanity Sees and Hears the Universe
Web References: 46th COSPAR Scientific Assembly scientific programme; COSPAR 2026
Image Credits: INAF
Keywords: Dark and Quiet Skies, satellite constellations, light pollution, radio-frequency interference, optical astronomy, radio astronomy, COSPAR, space sustainability, satellite technology, night sky, orbital debris, astronomy policy
