Science & Discovery
Satellite Constellations are a Colossal Threat to Astronomy
As private companies launch thousands of satellites into space, the light pollution problem is rapidly growing worse.
By Briley Lewis
Pexels/Photo by chris clark:
For decades, astronomical observatories have been safe havens for dark skies, protected from the encroaching lights of civilization: billboards, streetlights, house lighting, and more. The problem of light pollution — the unwanted presence of artificial light at night — isn’t a new concept. Now, however, even the most remote night skies are getting brighter and murkier, threatening our ability to learn about and connect with the cosmos. Studies in the journals Science and Monthly Notices of the Royal Astronomical Society show that two-thirds of major observatories are now affected by light pollution, and the problem is rapidly getting worse.
Light pollution reaches far beyond astronomy: It can harm wildlife, cause problems with human health including disrupting our sleep, wasting energy and contributing to climate change, and — of course — blocking our view of the night sky. According to the International Dark Sky Association, 80 percent of the world’s population lives under a polluted sky. Researchers also found that the night sky, on average, brightened almost 10 percent each year between 2011 and 2022. This means the night sky doubles in brightness every eight years, leading to “adverse impacts on astronomical observations, limiting scientific discoveries, cultural connections to the night sky, and opportunities presented by astrotourism,” wrote astronomer Antonia Varela Perez in her recent Science article on the topic. Losing our view of the night sky is harmful to human health, astronomy, wildlife, and our cultural connection to the cosmos.
A study published in 2023 found nearly 3 percent of all Hubble Space Telescope images captured between 2002 and 2021 had satellites streaking through the image. Shown here are four examples.
[Sandor Kruk, et al./Nature Astronomy volume 7, pages 262–268 (2023)]
Lights from human activity on the ground tend to be clustered around cities, which fortunately limits their geographical reach and allows for the creation of dark sky preserves. The situation in the sky isn’t as easy to work around. “The biggest threat towards the night sky is the dramatic uptick in the launching of satellites,” says astronomer Lindsay DeMarchi, who currently works on space policy in the U.S. Congress. The specific “satellites” DeMarchi is referencing are the satellite constellations, networks of hundreds to thousands of Earth-orbiting spacecraft launched by private companies. These spacecraft transform the problem of light pollution into a global issue, harming our shared views of space across borders and boundaries.
Urban light pollution leads to skyglow, which blots out all but the brightest night sky objects. The numerical values at the bottom of this illustration correspond to what's called the "Bortle scale," and is a way for citizen scientists to gauge how pristine or light-polluted their sky views are.
[NOIRLab/NSF/AURA, P. Marenfeld]
The threat to astronomy
“You can’t escape commercial Low-Earth Orbit (LEO) satellites, because constellations are designed to blanket the Earth and provide global coverage for various telecom services,” explains University of Washington astronomer Meredith Rawls. She is a member of the International Astronomical Union (IAU) Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (CPS).
“What we're experiencing now is what would happen if the automobile industry began using a single highway, never cleaned up a single accident — think: glass, bumpers, paint, hubcaps, handles, screws — and continued to produce new models of cars for consumers for over 100 years,” adds DeMarchi, highlighting the recklessness of our current plans for satellites around Earth. With little regulation, say astronomers, companies are constantly adding to the chaos, seemingly without regard for how it might impact the view from below. Satellite constellations blanket the whole night sky no matter where you are on Earth’s surface, including areas previously untouched by light pollution and professional astronomical observatory sites.
Astronomers are deeply concerned about how this will affect our ability to study the skies, both with the increasing overall sky brightness and due to visible satellites intruding on astronomical observations. That second concern includes some gloomy numbers: The Vera C. Rubin Observatory, for example, is slated to begin seeing the sky next year — and the observatory team predicts more than 30 percent of the images taken with this new facility will be unusable, contaminated with streaks from satellites soaring above.
Starlink satellites mar observations from professional observatories as well. The Dark Energy Camera, which uses the Víctor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIO) image, captured this view during a 333-second exposure on November 13, 2019.
[CTIO/NOIRLab/NSF/AURA/DECam DELVE Survey]
Even images taken with smaller telescopes, such as those captured by amateur astronomers observing from their backyards, are already being ruined by satellite streaks that seem to scratch an array of small lines into the picture. It is almost as if humanity will have to peer at space through a fence, unceremoniously blocked from the rest of the cosmos by the decisions of CEOs. These constellations are “fundamentally reshaping our skies,” says Rawls, “and I am personally frustrated that a small number of people and companies are able to alter the night sky for everyone so rapidly with such far-reaching consequences.”
Satellite constellations are a problem because of both their sheer numbers — nearly 8,000 are currently in orbit with up to 400,000 more planned by 2030 — and the characteristics of their orbits, which make them highly visible as sunlight glints off their surfaces. Some satellites are worse than others; the company AST SpaceMobile’s BlueWalker 3 is now “one of the top 20 brightest stars in the sky” says DeMarchi. A recent Nature paper dives into the results of a global observing campaign of this satellite.
“While this is just one prototype satellite, it is extremely bright, and is not the kind of thing we want to become the norm in low-Earth orbit,” adds Rawls.
Satellites pass through this night-sky view, a composite of 33 individual photographs. The satellites' reflections rival the brightness of the stars. (The bright streak at the image's right is a meteor.)
[Egon Filter/Wikipedia CC BY 4.0]
Envisioning a better future
It isn’t all gloom and doom. Astronomers are developing multiple paths forward to reduce the impact on ground-based astronomy and our view of the sky from Earth. Launching fewer satellites is the first obvious solution, but scientists have brainstormed other compromises, too.
One technological change to the networks of satellites that could help, suggest astronomers, is keeping their orbits below a certain altitude threshold. In addition, the astronomy community suggests designing the satellites so that they aren’t bright enough to be seen by the unaided eye. Committees and working groups, such as the IAU CPS, have also recommended that companies launching satellites make their orbital data readily available and accessible, to allow astronomers to coordinate their observations to not point in the direction of the offending spacecraft. When avoiding the streaks is unsuccessful, astronomers are also developing computational tools to deal with satellite artifacts left in their data, trying to salvage what they can from contaminated images.
Multiple groups are working toward these technological and computational goals. The IAU CPS is the major international leader for this issue, and it hosts workshops and develops recommendations for policymakers and companies. Recently, the committee even made an appearance at the 66th United Nations meeting as a major part of the agenda for the UN Committee on the Peaceful Uses of Outer Space, bringing the issue to the forefront of global discussion and policy. One of the IAU CPS divisions, SatHub, is working on quantifying the impact of satellite constellations to reveal the full extent of the issue. The American Astronomical Society also has a group focused on light pollution and satellite constellations that engages with companies to mitigate their products’ impacts on the night sky and rallies together astronomers from across the country to lobby for improved U.S. policy.
But, there’s one huge flaw in this plan, explains Rawls. “All brightness mitigations to date are voluntary, and they are only happening at all because astronomers willingly use their time to coordinate with satellite operators on a company-by-company basis,” she says. “I cannot envision this model scaling effectively.” To realistically tackle the issue of satellites blurring the sky, we need policies and legislation at all levels to keep companies in check.
Skyglow from a city lights up the horizon of this otherwise cosmic view.
[Pexels/Photo by Frank Cone]
SpaceX Starlink satellites streak across this photograph taken in 2019 and that captures the double star Albireo in Cygnus.
[Rafael Schmall]
Making better rules
The current state of international rules preventing light pollution and preserving the cosmos aren’t exactly comprehensive. “The only real ‘law’ is the Outer Space Treaty of 1967,” says DeMarchi, “which not every nation has signed, and many countries (namely the U.S.) are far behind in keeping their promises to uphold.” Some legislation has recently been passed at the country and state level; the Pennsylvania House of Representatives, for example, passed a light pollution bill following the guidelines of conservation group DarkSky International, and the U.S. Senate passed the ORBITS act for managing space debris. “As we speak, the House, the White House, and the Senate are busy with conversation surrounding mission authorization — a way of establishing a regulatory framework for in-space activities,” adds DeMarchi. Regulating launches could be an effective way of minimizing the impact of satellite constellations, by restricting the rate companies want to pump them into the sky.
Bureaucracy, government, and regulatory agencies move at a glacial pace, though, and passing laws takes a long time. Meanwhile, companies follow the classic Silicon Valley ethos of move fast and break things, and launch as many satellites as they want while the rules are in the works. “We need limits on the number of satellites that can be launched and in operation at any given time,” says Rawls. “We need limits on how bright they can be, and we need funding to verify these limits are being adhered to.”
The night sky should be used and enjoyed by groups and individuals, and without those regulations, satellite companies and their customers are taking the bulk of that enjoyment.”
“There is a lot of work to do,” adds Rawls.
Near-Earth space is getting crowded. This visualization includes 30,000 Starlink communication satellites, which is the number SpaceX initially proposed for its generation 2 constellation. As of this writing, the U.S. Federal Communications Commission has approved only a subset of that number.
[ESO]
How to help
Although the situation seems daunting, there are ways that even individuals can help. As with many other causes, educating your friends and family and talking to your local representatives are crucial; legislation starts at a local level, and politicians rely on their constituents for re-election. Communities in Arizona and Idaho have illustrated the power of consensus and local activism, successfully designating Tucson as a dark sky city and Central Idaho as a dark sky preserve, with certain rules and regulations to maintain darkness in those areas. The IAU CPS is also led by a community of volunteers, and could use more help from those with relevant professional experience and more funding to enable their work.
The satellite constellations mucking up the sky are a relatively new problem, and that youth is important and optimistic, says DeMarchi. “We can fix this,” she adds.
“Keep looking up, keep asking questions,” adds Rawls. “And don’t accept that the only possible future is one where we see more swarming satellites than twinkling stars.” ✰
(Published February 23, 2024)
BRILEY LEWIS (she/her) is a freelance science writer and Ph.D. Candidate/NSF Fellow at the University of California, Los Angeles, studying Astronomy & Astrophysics. Follow her on Twitter (X) @briles_34 or visit her website.
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