Astronomers look to preserve the night sky as thousands of satellites set to launch

The potential launch of tens of thousands of satellites — called constellations — is a serious threat to astronomy, according to the International Astronomical Union (IAU). Now, it's trying to find solutions.

Reflectivity of so many satellites would interfere with astronomical research, change views of the stars

The diagonal lines running across an image taken at the Lowell Observatory in Arizona on the night of May 25, 2019, shows trails of reflected light left by more than 25 of the 60 Starlink satellites as they passed through the telescope’s field of view. (Victoria Girgis/Lowell Observato)

The potential launch of tens of thousands of satellites is a serious threat to astronomy, according to the International Astronomical Union (IAU). Now, it's trying to find solutions.

The announcement came just days before SpaceX launched an additional 60 of its Starlink satellites

Such "constellations" — any collection of artificial satellites —  are already in wide use, powering the GPS in our cars and cellphones, for instance. But it's the massive number yet to come that has astronomers around the world deeply concerned.

"We are used to some satellites crossing the night sky, but now we're talking about thousands, some that would be bright enough to see with the human eye," said Piero Benvenuti, an adviser at the executive committee of the IAU, which has more than 13,000 members worldwide.

A series of lights in the night sky.
Seen here is a trail of almost 60 satellites recorded by Marco Langbroek. The Starlink satellites were launch atop a Space X Falcon 9 rocket on May 23, 2019. (Marco Langbroek)

In all, SpaceX plans to launch as many as 42,000 satellites, and it's not the only one. Amazon plans to launch roughly 3,200 satellites, and OneWeb's 650 satellites. Canada also plans to launch 300 Telesat satellites.

The goal of Starlink is to bring internet connectivity to every part of the world, a goal similar to OneWeb's.

And while astronomers agree that goal is a practical one, they are concerned over not only the loss of the night sky, which is already under threat due to light pollution, but also to large-scale and very expensive observatories, like the $1 billion US, 8.4-metre, ground-based Large Synoptic Survey Telescope

There are more and more of these all-sky surveys being put into place. Instead of looking at a small patch of sky, they scan large swaths. But moving satellites create long streaks of light in the images collected.

Around 19 Starlink satellites were imaged by DECam on the Blanco 4-metre telescope at the Cerro Tololo Inter-American Observatory (CTIO) shortly after launch in November 2019. The gaps in the satellite tracks are due to the gaps between the DECam CCD chips. (NSF’s National Optical-Infrared)

"Apart from their naked-eye visibility, it is estimated that the trails of the constellation satellites will be bright enough to saturate modern detectors on large telescopes," the IAU statement said. "Wide-field scientific astronomical observations will therefore be severely affected."

'Pristine' night sky

Reports of the visibility of a "train" of Starlink satellites began last May, shortly after the first batch of 60 were launched. Astronomers, both professional and amateur, posted videos and photos of the long streak of satellites dotting the night sky.

Then, in December, more satellites were launched. 

But while the threat may be most felt by professionals, the IAU statement noted, "The appearance of the pristine night sky, particularly when observed from dark sites, will nevertheless be altered, because the new satellites could be significantly brighter than existing orbiting man-made objects."

As a result, the IAU, as well as other organizations like the American Astronomical Society, sought out professional astronomers to run simulations showing what would happen with tens of thousands of satellites in orbit around Earth. The hope was to not only better understand the consequences but also head toward some solutions.

Preliminary findings

They found that, using an example of 25,000 satellites in low-Earth orbit — which ranges from 160 to 2,000 kilometres above Earth and with orbits between 84 and 127 minutes — at any given point, satellites above the horizon could number from 1,500 to a few thousand. 

Some other notable findings:

  • While most would lie near the horizon, roughly 250 to 300 of those would appear in a part of the sky where most of astronomical observations are conducted (roughly 30 degrees above the horizon).
  • When the night sky is darkest, there could be 1,000 satellites visible at once, until they enter Earth's shadow and become less visible. 
  • The trains of satellites are most visible shortly after initial launch. 
  • While the IAU's focus is on optical telescopes, radio telescopes are also in jeopardy.

Benvenuti is keen for more research in order to better understand what the effects of tens of thousands of satellites could be. Right now, he said, astronomers are working with SpaceX in an effort to reduce their reflectivity — called albedo — and trying to work with other companies as well. 

Connie Walker, an astronomer and president of the Commission B7, which is involved in the IAU constellation analysis, said the idea is to find a solution suitable for everyone.

"It's going to be a long process, and I think to some extent, the various companies producing these satellite constellations are willing to try to come up with some solutions," she said. Some of the ideas being examined, she said, are changes to the coatings of the satellites and changes to software to help observatories avoid, or compensate for, albedo.

But, she said, there is unlikely to be one quick-fix that will check off all the boxes.

Moving forward

The launch of satellite constellations and their consequences have largely taken the astronomical community by surprise. One of the problems is that there is no regulation surrounding the albedo of an object in orbit.

But that might change.

WATCH: A train of Starlink satellites crosses the sky (on the right)

The IAU plans to bring the issue to the UN Committee on the Peaceful Uses of Outer Space (COPUOS) in the coming months. They also plan to include the issue of constellations and their threat to science in the program of the Conference on Dark and Quiet Skies for Science and Society, held by the IAU, the United Nations Office for Outer Space Affairs and the Government of Spain in October.

"We don't want to stop the progress of having this G5 interconnectivity," Benvenuti said. "But one has to consider the implications that you're creating on the environment, and in particular the night sky." 

And, he added, "We don't want to cry wolf and say it's a disaster and you can't do astronomy anymore."

But astronomy is more than just looking up at the night sky, admiring the stars or photographing them. It's about advancing knowledge and even technologies. 

"The progress that we've made in the last 100 years … It's absolutely astonishing how much we've learned because of astronomical observations," he said. "When you use your GPS, you apply Einstein's relativity, otherwise you wouldn't know where you are. People tend to forget about this."


Nicole Mortillaro

Senior reporter, science

Based in Toronto, Nicole covers all things science for CBC News. As an amateur astronomer, Nicole can be found looking up at the night sky appreciating the marvels of our universe. She is the editor of the Journal of the Royal Astronomical Society of Canada and the author of several books. In 2021, she won the Kavli Science Journalism Award from the American Association for the Advancement of Science for a Quirks and Quarks audio special on the history and future of Black people in science. You can send her story ideas at