Washington, D.C., June 2025
AAS Statement on Satellite Proliferation
Adopted 8 June 2019, Revised 7 June 2025
The American Astronomical Society (AAS) notes with concern the accelerating deployment of large constellations of satellites into Earth orbit. The number of satellites in low-Earth orbit (LEO) has risen exponentially in recent years, and over one million satellite license applications have been filed for deployment over the coming decades at the International Telecommunication Union (ITU), creating the potential for substantial adverse impacts to ground- and space-based astronomy if only a fraction of these systems come to fruition as well as the long-term sustainability of the orbital environment. These impacts include disruption of optical and infrared observations by direct detection of satellites and space debris in reflected and emitted light (optical and infrared); contamination of radio astronomical observations by electromagnetic radiation, including unintentional emission outside of allocated satellite communication bands; and proliferation of space debris due to collisions that may render portions of Earth’s orbit unusable for the foreseeable future.
The AAS recognizes that outer space is an increasingly available resource with many possible uses. However, the potential for large satellite constellations launched by nations around the world to adversely affect both each other and the study of the cosmos is becoming increasingly apparent, both in LEO and beyond. Modern space situational awareness requires international coordination, and astronomers can offer unique perspectives to inform these efforts, as has been recognized in diplomatic fora including the United Nations Committee on the Peaceful Uses of Outer Space (UN COPUOS), which adopted a 5-year agenda item in 2024 to study the impacts of satellite constellations on dark and quiet skies and ground-based astronomy.
Additionally, the components of satellite constellations undergo planned deorbit to mitigate the proliferation of space debris. However, deposition of metal and black carbon particles in the atmosphere from satellite launches and deorbits may impact global climate and the integrity of Earth’s ozone layer, while larger mechanical components on uncontrolled reentry trajectories risk damaging human life and property on the ground, both from impacts and pollution. The AAS encourages the broader scientific community to continue to study the potential global environmental impacts of satellite constellations and communicate findings to appropriate groups.
The AAS is actively working to assess the impacts on astronomy from large satellite constellations and mitigation strategies as their numbers rise further. Only with thorough and quantitative understanding can we properly assess the risks and identify appropriate mitigating actions across scientific, regulatory, and socially impacted communities. The AAS desires that this be a collaborative effort among its members, other scientific societies, and other space stakeholders, including private satellite companies and the U.S. federal government. The AAS will support and facilitate the collaborative work by relevant parties to understand fully and minimize the impact of large satellite constellations on ground- and space-based astronomy.
To this end, the AAS endorses IAU Resolution 2024 #1 “for the Protection of the Dark and Quiet Sky from harmful interference by satellite constellations” as guidance for establishing priorities for mitigations.
AAS Resolution on Light Pollution
Adopted 4 January 2017, Revised 7 June 2025
Astronomy has benefited from dark skies for thousands of years, but now the rapid growth of artificial sky glow – as fast as 10% per year – is jeopardizing all of humanity’s ability to see, study, and enjoy the cosmos from the Earth’s surface. More than half of all major observatories worldwide now operate under skies that are significantly brighter than natural darkness. Abundant scientific research demonstrates that light pollution also disrupts natural ecosystems, harms human health, and wastes energy.
To realize its mission to enhance and share humanity’s scientific understanding of the universe as a diverse and inclusive astronomical community, the AAS calls on its members to enact the following lighting principles locally, regionally, and nationally in support of the protection and restoration of dark skies. Artificial light at night should be:
Useful: Start with natural darkness and add light only if needed. Areas around observatories should be kept naturally dark.
Targeted: Use shielding to target the direction of light so that it points downward and does not spill beyond where it is needed. Glare should be minimized.
Low Level: Light should be no brighter than necessary. Use the lowest light level that will serve the intended purpose.
Controlled: Use controls such as timers or motion detectors to ensure that light is available only when it is needed, dimmed when possible, and turned off when not needed.
Warm-colored: Limit shorter wavelength (blue-violet) light to the least amount needed. When light is needed near major observatories and sensitive natural sites, it should be monochromatic and long wavelength.
In conjunction with this call to action, which is aligned with DarkSky International / Illuminating Engineering Society’s joint statement, “Five Principles for Responsible Outdoor Lighting,” the AAS endorses:
- IAU 2009 Resolution B5 “In Defence of the Night Sky and the Right to Starlight,” affirming that access to a dark night sky is a universal human right, making quality outdoor lighting a worldwide imperative;
- the American Medical Association’s CSAPH Report 2-A-16 (May 2016) on “Human and Environmental Effects of Light Emitting Diode (LED) Community Lighting”;
- the United Nations Office of Outer Space Affairs / IAU Dark & Quiet Skies I and II reports and recommendations (2020, 2022) for stopping and reversing the growth of light pollution and artificial sky glow; and
- the United Nations Environment Programme / International Union for the Conservation of Nature’s report, “The World at Night: preserving natural darkness for heritage conservation and night sky appreciation” (2024).
AAS Resolution on the Protection of Radio Frequencies Used for Radio Astronomy
Adopted 11 June 1995, Revised 7 June 2025
Radio wavelength observations are crucial to the field of astronomy due to the unique perspectives they offer. Radio telescopes are able to produce high-resolution images via aperture synthesis, revealing the detailed structures of astronomical objects. Studies of quasars, galaxy dynamics, the cosmic microwave background, pulsar timing, and cosmic magnetic fields among others almost uniquely benefit from study by radio waves. However, the radio spectrum is a finite natural resource with many different services vying for access. Distant astronomical signals are many orders of magnitude fainter than human-produced radio transmissions for communications. It is for these reasons that specific astronomically important radio bands have historically been internationally protected.
The continuing protection of radio astronomical observations is of great interest to the American Astronomical Society (AAS). The AAS strongly endorses the maintenance of international allocations for the radio astronomy service and domestic regulations supporting the protection of these allocations and broader frequency bands at the small number of special geographic sites where radio astronomy telescopes are located. As technology develops, new concerns arise. Of particular concern is the growing congestion of the radio spectrum caused by an ever-increasing demand for wireless communications services, especially in space-based operational paradigms. The expansion of satellite constellations means that traditional methods of mitigating radio frequency interference at telescopes –– including siting facilities in remote locations and using natural terrain to attenuate transmissions – are becoming less effective. Radio Quiet Zones (RQZs) are regions in which the usual spectrum allocations are modified for the protection of astronomy and other passive services within a certain region. One such RQZ is the National Radio Quiet Zone (NRQZ) around the Green Bank Observatory in West Virginia. However, there are many radio astronomy observatories which have no established RQZ. The AAS endorses the establishment of new RQZs for the Very Large Array, the Very Long Baseline Array, DSA-2000 and other remote sites. Additionally, with the growing population of transmitting satellites in low-Earth orbits, RQZs within the United States and internationally (such as within Chile), which were originally established when the primary requirement was to mitigate impacts from ground-based sources, may provide insufficient protection for astronomical telescopes located within their borders. The AAS endorses the incorporation of coordination requirements within RQZs that will mitigate the impact of satellites on astronomical telescopes. Additionally, protection of radio astronomical bands must account for unwanted emissions from transmissions in nearby bands and harmonics, as such unwanted emissions have the potential to severely disrupt radio astronomical observations.
In response to the novel challenges, especially with expanding satellite constellations, the AAS supports ongoing efforts to develop innovative means of coexistence between radio astronomy systems and wireless communications services. In particular, dynamic spectrum sharing techniques and active coordination between radio astronomy facilities and wireless operators (both satellite and terrestrial) offer opportunities to preserve the operations of both commercial services and radio astronomy while fostering long-term positive collaborations between academia and industry. Current efforts working towards these goals should continue.
The AAS also notes with concern that several satellite constellation operators are advancing towards an operational model known as Supplemental Coverage from Space (SCS) in which satellite transmissions are received directly by cell phones rather than from base stations in fixed locations. This model makes use of very high-power satellite transmissions and large spot beams due to the frequency bands and satellite antenna sizes used, making geographic avoidance of radio astronomy sites difficult. Traditional means of coordination within RQZs may become ineffective if SCS is adopted by satellite operators worldwide. Innovative dynamic spectrum sharing projects are therefore critical for ensuring that radio astronomers can continue conducting research from Earth, but dynamic spectrum techniques may not be feasible if too many SCS bands are adopted. The AAS supports the adoption of as few SCS bands as possible and close coordination between SCS operators and radio astronomy observatories to minimize impact.
The AAS supports comprehensive studies within the International Telecommunication Union (ITU) process leading to recommendations especially for the protection of the RQZ in Chile where ALMA, CMB experiments, and the Event Horizon Telescope operate from satellite constellation transmissions, and broader recommendations for other radio astronomy facilities worldwide at the 2027 World Radiocommunication Conference (WRC). The AAS endorses the recommendations provided by the National Academies Committee on Radio Frequencies for WRC-27.
Additionally, the AAS endorses the radio astronomy recommendations in the International Astronomical Union (IAU) Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (CPS) Call to Protect the Dark and Quiet Sky from Harmful Interference by Satellite Constellations. In particular, the AAS recognizes the importance of limiting unintended electromagnetic radiation (UEMR) from satellites, since UEMR in the 50 – 200 MHz range can be especially problematic to astronomical experiments seeking to confirm the Epoch of Reionization. The AAS supports ongoing efforts to better understand and characterize UEMR to find effective solutions to mitigate impacts.