27 September 2023

The dark side: Should astronomers have sole control of the night sky?

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David Grossman* says new man-made satellite constellations are causing concern among amateur and professional stargazers.

Photo: Alexander Andrews

Last month’s launch of Starlink satellites was a moment long planned by Elon Musk and SpaceX.

Known as a satellite constellation, the company has sent 60 of a planned 1,200 satellites into orbit.

What they did not expect, though, was backlash from the International Astronomical Union (IAU) and the International Dark Sky Association.

The Starlink constellations, it turns out, could be threatening the study of the night sky.

The IAU has issued a statement saying it is “concerned” about satellite constellations and what they mean for the future of astronomy.

“We do not yet understand the impact of thousands of these visible satellites scattered across the night sky and despite their good intentions, these satellite constellations may threaten both” nocturnal wildlife and astronomical research,” the IAU says.

The risks are twofold — the satellite constellations could affect both visible and radio waves.

The “surfaces of these satellites are often made of highly reflective metal, and reflections from the Sun in the hours after sunset and before sunrise make them appear as slow-moving dots in the night sky,” reads the IAU press statement.

“Although most of these reflections may be so faint that they are hard to pick out with the naked eye, they can be detrimental to the sensitive capabilities of large ground-based astronomical telescopes”, like the Hobby–Eberly Telescope in Texas.

It’s more than a hypothetical.

Victoria Girgis, of Lowell Observatory in Flagstaff, Arizona, told NPR about a moment when Starlink satellites moved in front of distant galaxies she was studying.

“My first immediate reaction was, ‘that’s visually kind of cool,’” she says.

“But my second reaction was, ‘man, you can’t see a single galaxy.’”

From a radio wave perspective, the IAU is worried that even if precautions are taken to keep the satellites from interfering, “aggregate radio signals emitted from the satellite constellations can still threaten astronomical observations at radio wavelengths.”

Radio waves have been responsible for some of the biggest astronomical discoveries of the last decade, including the first ever photograph of a black hole.

It’s not just scientific observations that might be at risk.

The International Dark Sky Association (IDA), which promotes the concept of night skies without light pollution, has issued a statement saying that “we do not yet understand the impact of thousands of these visible satellites”.

“The reason that this issue is now on our radar, and that we have gone on record with an opinion about it, is that Starlink and competing satellite constellations have the potential to radically remake our experience of the night, whether as casual stargazers or professional astronomers,” astronomer John C. Barentine, IDA’s Director of Public Policy, told Popular Mechanics.

“As someone who cares deeply about the night and our access to views of the universe, seeing the Starlink object train pass over Tucson two nights after launch was jarring,” he says.

“And it became clear by the end of that weekend, based on member feedback and comments on our website, that we had to do something.”

While satellites have orbited the globe for decades, they’ve never reached the numbers of current satellite constellations.

Exact numbers are hard to come by, but estimates in 2018 showed that 1,980 active satellites were orbiting the planet.

The situation is already troubling without satellite constellations to worry about, Barentine says.

“Facilities like Palomar [Observatory] and Mt Wilson, in California, now suffer from light pollution to the point where their utility is really limited,” Barentine says.

“If we could get a lid on the problem of skyglow, these 70-plus-year-old facilities would still be doing cutting-edge science.”

But now, piling tens of thousands of new satellites on to the thousands already in orbit will strain even the latest and greatest facilities.

And, as we continue to push technology and facilities to the absolute limits, it makes the problem of a night sky polluted with skyglow or artificial satellite trails all the more acute.

Satellite constellations are being sent into space with clear purposes — in Starlink’s case, to expand internet access to countries lacking infrastructure.

The IAU and IDA both acknowledge these as worthy goals, Barentine says, saying there are “good reasons to put objects in orbit for their clear benefits to humanity.”

SpaceX CEO, Elon Musk reaffirmed those reasons in a tweet, saying that “potentially helping billions of economically disadvantaged people is the greater good” in the situation.

“That said,” Musk adds in the tweet, “we’ll make sure Starlink has no material effect on discoveries in astronomy.”

“We care a great deal about science.”

But Barentine is sceptical that an easy solution will be found.

“Simply making the satellites dark in order to reflect less sunlight probably won’t work, because the emission and re-radiation of heat can actually push on the satellites and change their orbits,” Barentine says.

“Sending them up to higher orbits doesn’t seem feasible, either, because it would then involve stronger radio transmissions to and from the ground — which will certainly have an impact on radio astronomers’ work.”

But neither side will likely be going anywhere.

“The bottom line,” Barentine says, “is that there doesn’t seem to be an approach here that will satisfy both parties, one that puts objects of a particular nature into particular orbits that render them essentially invisible to astronomers but that also enables achievement of the technical goals of the satellite constellations.”

* David Grossman is a staff writer for PopularMechanics.com. He tweets at @davidgross_man.

This article first appeared at www.popularmechanics.com.

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