The statistics are stunning: More than 80% of the world’s population (and more than 99% of those in the U.S. and Europe) live under light-polluted skies. Most people can’t see the Milky Way. All this artificial sky glow has real impacts, affecting everything from insect reproduction to bird migration to crop yields to human health. Yet over the last 25 years, light pollution has only increased, by at least 50% overall — and in some areas, it’s up 400%.

More recently, the problem of light pollution has expanded in an unexpected way. The growing number of artificial satellites in low-Earth orbit (LEO) are increasingly adding moving lights, glints, and even diffuse glow to the night sky. Over the past two years, the number of active and defunct satellites has doubled, to a total of about 5,000 as of March 30, 2021. And companies have filed to launch tens of thousands more into orbit within the decade. While astronomers have always traveled away from civilization to reach darker skies, now satellites will streak across the fields of view of even the most rural telescopes.

Astronomers are engaging with satellite companies, such as in two conferences dubbed SATCON1 and SATCON2, which took place in the summers of 2020 and 2021, respectively. But the challenges facing satellite operators and astronomers alike are daunting.

Now, to bring the issue to a higher level — and address ground-based and space-based lights in one fell swoop — these issues are going to the United Nations. Astronomers, dark-sky advocates, industry representatives, and members of the UN’s Office for Outer Space Affairs took part in the Dark and Quiet Skies for Science and Society workshop on October 3–7, 2021. (The conference was virtual, not because of COVID-19 but because of an active volcano in La Palma, Spain, which was where the workshop was to have taken place.)

Artificial Lights at Night

Reducing light pollution doesn’t have to mean eliminating lights; outdoor lighting just needs to be directed where it is needed, when it is needed. And critically, any outdoor lights should be amber-colored, rather than the white/blue LEDs that disrupt the circadian rhythms of humans and wildlife alike.

Simple enough, right? So why aren’t we doing these things? Some individual cities have instituted dark-sky lighting ordinances. Pittsburgh, Pennsylvania, did so recently, and Tucson and Flagstaff in Arizona have and continue to implement even stricter measures in place, in part to protect nearby observatories. Representatives from Morocco and China gave updates during the conference on dark-sky efforts, and Andreas Hänel (Dark Sky Germany) reported that his country has particularly strong participation in dark-sky measures.

While such grass roots actions are difficult to implement and unevenly distributed, they also provide crucial examples to guide broader policies. “You want best practices that can be applied internationally, unilaterally, for all satellites,” suggested space diplomat Peter Martinez. “Use the outcomes of bottom-up efforts as inputs to move toward a set of international guidelines that could be adopted by the UN General Assembly.”

However, the secretary of the Committee on the Peaceful Uses for Outer Space (COPUOS), Niklas Hedman, cautioned that the committee might not consider ground-based light pollution as part of their purview. “We have to be careful so COPUOS doesn’t dismiss it,” he said at a final roundtable.

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Satellite Constellations

Sky & Telescope has extensively covered the impact of satellites on ground-based observing and astronomy. And, as presenters at Dark & Quiet Skies made clear, even space telescopes aren’t immune to satellite interference. Observatories such as the Hubble Space Telescope and the exoplanet-characterizing CHEOPS satellite have both reported seeing spurious flashes from satellites.

Mitigations, though more complex than in the case for light pollution, can help. For example, SATCON1 recommended that satellites be no brighter than 7th-magnitude when orbiting at 500 km, putting them out of reach of naked-eye observers. Satellites at higher altitudes, where satellites are more visible for longer in the night, would need to be even dimmer. Software and up-to-date databases will also help avoid satellite trails across astronomical images, or at least mask them when they do occur.

But mitigations have also been difficult to implement. While SpaceX has made considerable progress in dimming its Starlink satellites, they haven’t yet reached the 7th-magnitude goal that SATCON1 set out. And while OneWeb and Amazon’s Kuiper have both made pledges of corporate responsibility, Olga María Zamora Sanchez (Institute of Astrophysics of the Canary Islands, Spain) reported at the workshop that the 321 OneWeb satellites launched so far are still too bright at longer wavelengths.

Likewise, databases and software to predict satellite passes and mask trails take time and funding to develop, notes Jonathan McDowell (Center for Astrophysics, Harvard & Smithsonian), who led an algorithms group during SATCON2. Right now, most of these efforts have occurred in astronomers’ spare time.

And even if the mitigations were 100% successful, they wouldn’t be enough. “All of these mitigations have a regime where they might be helpful,” McDowell says, “and then a regime where you’re just swamped, and no mitigation will save you.” LEO can probably carry 100,000 satellites, maybe even a million with advances in technology. At great enough numbers, telescopes will no longer be able to avoid photographing satellite trails, and with multiple trails per image, they’ll become impossible to mask.

“The policy challenge is making sure we never get to that regime,” McDowell argues. “We need international action to preserve the space environment and the night sky.”

The Night Sky as Environment

To that end, space lawyer Charles Mudd advocated at the conference that Earth’s orbital space be considered a natural resource and an integral part of our planet’s environment —and regulated as such.  

“It’s clear that all our colleagues would like this to be made an environmental issue,” says organizing committee member Richard Green (University of Arizona). “It would be a broader solution for sure.”

But while successful dark-sky efforts in Europe have been grounded in environmental protection, that approach is less likely to work in the United States, Green notes. “If you have to create an environmental impact study, it’s a big deal,” he says. “It takes years, and it’s very expensive.”

There are lots of other, albeit narrower ways to approach the issue, he adds. “If it spoils the value of National Parks, that’s another agency’s mission. If it makes searching for Earth-impacting asteroids more difficult, that’s another agency’s mission.”

For their parts, industry representatives of SpaceX, Amazon, and OneWeb have all been pushing for corporate responsibility and citizenship in place of regulation, and they have encouraged international operators to do the same.

“On the other hand, if it turns out to be harder or more expensive, the bottom line is what counts,” Green says. “It would be good to have regulatory incentives to make sure they stick to that good intention.”

What Happens Next

The road from dark-sky-friendly guidelines to regulation and enforcement is a long and rocky one. COPUOS must balance the needs of its now 100 member states, some of which already host top-notch space industries and some of which are just emerging into the field. For this and other reasons, COPUOS is more likely to institute a resolution that would be up to the member states to enforce, rather than a binding treaty.  

But whether that is what the committee will recommend is still to be decided. The workshop report, still forthcoming, will be an official UN document that will go to the Scientific and Technical Subcommittee of COPUOS. If approved as a resolution, it will go to COPUOS itself. It could even go to the General Assembly.

“Do we have a definite way forward, with a good shot at COPUOS endorsement?” Green ponders the question. He notes that despite the compelling legal arguments, there could be hesitation to engage with anything that might reinterpret the Outer Space Treaty. “I don’t know which arguments are going to win the day.”

Further reading:

Report issued following SATCON1
Report issued following SATCON2
Report issued following Dark & Quiet Skies 2020

(The link to the report from the most recent UN workshop will be added here when available)