Starlink and other megaconstellation satellites pose a real problem to astronomy.

Update (March 6, 2020): The European Southern Observatory has released a study on the impact of megaconstellation satellites on astronomical observatories around the world, finding that large telescopes will be "moderately" affected, while wide-field surveys, such as the Rubin Observatory in Chile, will be "severely affected." Find more details on the study in the ESO press release.

By now many of us have seen the photo of the Starlink satellite train launched by SpaceX crossing the field of view of a professional telescope, and perhaps also the video of Starlinks interfering with a meteor-monitoring video camera.

The shots are dramatic — even shocking — but they’re also a bit misleading. The real problems that Starlink and other so-called megaconstellation satellites pose are actually more insidious.

Starlinks cross DECam image
Early morning on Monday, November 18th, Cliff Johnson (Northwestern University) and colleagues took this image using the Dark Energy Camera on the 4-meter Blanco Telescope at the Cerro Tololo Inter-American Observatory. Nineteen Starlink satellite trails crossed the image during the six-minute exposure. The image was taken as part of the DELVE survey, which is mapping the outskirts of the Magellanic Clouds, as well as much of the southern sky in search of new dwarf galaxies orbiting the Clouds or the Milky Way.

The Starlink Train

As with the last Starlink launch in May this year, the most recent launch placed 60 satellites in a staging orbit. The staging orbit for the first 60 was 440 km (273 miles); for the ones just launched in November, it was only 280 km. This is the altitude where SpaceX first communicates with and checks out its satellites, and it’s low on purpose. If a satellite fails, and several from the May launch did fail, then it can passively de-orbit from this lower altitude and re-enter Earth’s atmosphere fairly quickly, rather than remaining on as space junk. SpaceX claims the failed satellites from the May launch will burn up within a year; presumably, the more recently launched satellites will deorbit even more quickly.

What this means for observers is that, until the satellites have undergone testing and have moved to higher altitudes, they’re going to look really bright. The satellites launched in May first appeared around magnitude 2, similar in brightness to Polaris, but by July they appeared around magnitude 6, just within reach of the unaided eye at dark-sky sites. A similar pattern should occur for the second batch.

What’s more, the satellites are all bunched together following their deployment, like a wagon train of stars moving through the sky. That lends some serious drama to any photograph, of course. But they won’t stay in that configuration for long. For their first 1,584 satellites, SpaceX has FCC approval for 24 orbital planes of 66 satellites each. So, once they’ve started operations, if you’re looking in any given orbital plane, you’ll see satellites spread out 22 minutes apart.

The Global Meteor Network posted this video of the Alpha Monocerotid meteor shower. Starlink satellites start streaking across the frame starting at the 2:12 mark.

Finally, contrary to headlines claiming the ruin of astronomical exposures, the passage of the Starlink train over the Dark Energy Camera posed only a modest loss to the astronomers involved. “Although we never want to lose pixels (and valuable data), the impact to this exposure was to approximately double the number of bad pixels, and the overall effect was moderate,” says Cliff Johnson (Northwestern University), an astronomer involved in the observations.

That all sounds like good news, right? Except that each batch of satellites spends perhaps 5% of its lifetime reaching operational altitude. Depending on how many launches are occurring — and SpaceX and another company, OneWeb, are both aiming for a high frequency of launches — the satellite train could become a more common sight.

The Problem with Satellites

However, the real problem actually occurs when the satellites reach operational orbits. Current photos and videos of the satellite train can’t accurately capture the near-future situation we're facing.

Neither can the nearest precedent we have, the 66-satellite Iridium constellation that enables satellite phones and pagers. These satellites appear at similar magnitudes to the Starlink satellites and have been around more than 20 years. Iridium demonstrates that the mere existence of a few magnitude-6 satellites is not an issue. Rather, it's a numbers game: If SpaceX fills out its planned 12,000-satellite Starlink constellation, or its proposed 42,000-satellite constellation (though the latter plan doesn’t have international or federal approval yet), astronomy will change forever — though maybe not quite in the way pictured above.

This simulation, by Michael Vlasov and published on DarkySkyWatch, shows what our future night sky might actually look like (with a few simplifying assumptions). It’s not as dramatic as shots of the Starlink train, but it’s no less problematic for astronomy.

At operational altitudes, the satellites will be fainter and more spread out than the photos and videos that have made the rounds online, making them less obvious to the unaided eye — but they'll be plenty visible to cameras and other astronomical instruments.

The upshot is, even after megaconstellation satellites fade, they'll be distracting for visual observers in dark-sky locations. They'll also be problematic for nightscape photographers, who can't easily process out satellite trails. And they'll pose a real dilemma for professional astronomy, where wide and deep surveys to study everything from cosmology to near-Earth asteroids are becoming the norm.

We take a deep dive into the subject of megaconstellation satellites in the March 2020 issue of Sky & Telescope. If you're an astronomer or stargazer, or even if you just want to be, you'll want to check this article out to learn the full gamut of unintended consequences for visual astronomy, astrophotography, professional optical astronomy, professional radio astronomy, and space debris. This issue will be on newsstands in late January.

What Will the Future Hold?

SpaceX, and to some extent OneWeb, are already in conversation with professional astronomers, largely as a result of the furor following the May Starlink launch. Due in part to these conversations, SpaceX has announced its intention to paint parts of its future Starlink satellites a matte black, which could decrease their visual magnitude by as much as 3.5. (The announcement came shortly before the November launch, and the date of the black-satellite rollout remains under wraps for now.)

OneWeb, on the other hand, has not mentioned any plans for utilizing black paint, focusing instead on placing its smaller satellites in higher, 1,200-km orbits. They'll be a little fainter there, by two or three magnitudes, but not enough to prevent consequences. At higher altitudes, they'll also be visible for longer periods at night.

Given that every aerospace company could take a different approach to the problem facing astronomy, it’s clear that if we want to protect the night sky, we can’t rely on goodwill alone. Let’s just make sure that we engage using facts, not frenzy.

“The best grassroots action that Sky & Telescope readers can take at this point is to educate themselves about the verifiable and likely potential impacts of this coming technological leap and then work to educate their communities and elected leaders about it,” says Deputy Executive Officer Joel Parriott at the American Astronomical Society.




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Mike Fidler

December 3, 2019 at 5:28 pm

This issue is only going to effect the night sky during astronomical twilight and not later. These satellites will then be in earth's shadow since they are at a much lower altitude. No one in the astronomy community seems to be mentioning this. Remember over 3 billion people have no access to the internet and 5 BILLION do not have 25mbs that the major cities in the USA have. We forget how small (5%) a country the USA is when compared to the rest of the world's population.

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Monica Young

December 3, 2019 at 8:01 pm

Hi Mike, that's a great point, and one that I address in the feature. How far into the night a satellite is visible depends on its altitude as well as on the observer's latitude. The megaconstellations being proposed are at a wide variety of altitudes in low-Earth orbit. Lower altitudes mean brighter satellites, but they're also visible for less of the night; satellites in higher-altitude orbits will be fainter but visible for more of the night. And latitude matters: At high latitudes in summertime, satellites will actually remain visible for most of the night. Cees Bassa has tweeted some visualizations of satellite visibility (such as the one here: and we feature his work in the feature as well.

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December 4, 2019 at 4:19 pm

I was imaging M42 a couple of nights back here in the UK, offset to try and catch the NGC1999 in the frame, and every single exposure (20s to 180s) showed at least 3 Starlink satellites passing below NGC1999. The magnitude varied slightly, the track varied slightly, but they kept coming throughout the hour I was imaging that area. Watching the track the satellites were taking, I gave up, and sure enough processing the stacked images did not remove the trails, as some seem to be on exactly the same track. This was 22:00 - 23:00 at 52N - the sun had disappeared below the horizon 4-5 hours earlier and, when I gave up, was due up in 6 hours... if the satellites are visible to imaging at 23:00 in the winter, they are going to be visible to imaging all night long, all year round, until they get to the operating altitude.. maybe even then.

As for the 3 billion people who do not have access to the internet, the majority of those also don't have access to electricity and/or the minimal wealth to afford Elon's terminals, unless he plans to give them away?

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Andrew James

December 6, 2019 at 8:32 pm

Your point is well taken regarding access to the Internet by humanity is agreed, but isn't there perhaps a better engineering solution to the problem that does not damage the environment or our ability to explore the Universe?
Doesn't Starlink design and deployment mostly based on reducing the commercial costs and making profit rather than human need to observe the sky? Is there a better and less damaging way to achieve this aim?
Also saying "We forget how small (5%) a country the USA is when compared to the rest of the world’s population." is a plain contradiction, as the full deployment will affect 100% of the world's population. e,g. So 95% of the population have no say in their own desire to observe the Universe?
Total investment in ground-based astronomy is significant for many countries, being a global undertaking toward uniting our human desire of exploration and collaboration without the weight of commercial gain or nationalistic competition. e.g. Pure science. Astronomy is one of the the final bastions that hasn't been totally destroyed by vested interests. Sacrificing this might be an awfully high price that we may well rue for our future generations.
IMO astronomical endeavours must be defended and protected at all cost.

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Anthony Barreiro

December 3, 2019 at 6:07 pm

Do we want to have a window onto the rest of the universe, or a mirror reflecting back tweets and HD videos onto every square centimeter of the Earth's surface? It's too bad we need to rely on the good will of an unlimited number of unregulated high tech entrepreneurs. Even if most of them make every possible accommodation, the sheer number of satellites in multiple arrays will be problematic, and one or a few bad actors would have a huge negative effect.

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December 4, 2019 at 2:45 am

I wonder what uncontacted tribes in places like Brazil are making of this.

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December 4, 2019 at 6:20 am

Nice to see a more thorough article, as well as the promise of more to come. The obvious question from outsiders (disclaimer: I do have an interest in astrobiology and so cosmology) is why the regulatory process, the satellite traffic oversight, and - it seems - the astronomical society - are all unprepared?

The process seems mainly commercial/military though I gather radio astronomy has protected bands; the satellite traffic oversight has reportedly no enforced avoidance procedures (so e.g. Starlink satellites will be self guided to avoid collisions and can go anywhere within the orbit corridor), and the astronomy society seems to have no weight or even communication insight whatsoever (s e.g. the launch trains are coming as surprises instead of as planned interrupts)..

Hopefully the upcoming articles will go over some of that. The same reactive-instead-of-proactive process can be seen in regards commercial interplanetary traffic impact on astrobiology (e.g. the dead but still organic contaminants of stealth tardigrades on the Moon, adding to the Apollo waste bags).

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December 5, 2019 at 12:55 am

don't forget the impact on infra-red and radio astronomy. black paint won't work there.

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Andrew James

December 6, 2019 at 7:27 pm

The argument for this sadly falls back to imposing exploitation, politics and singular domestic national commercial interests - regardless of moral damage it may cause or the collective wishes of humanity or other nations. Worst the launching of all these satellites plainly ignores international agreements - the peaceful and specific non-commercial use of space. If saying : "For their first 1,584 satellites, SpaceX has FCC approval for 24 orbital planes of 66 satellites each." is true, then the problem is really down to the Federal Communications Commission (FCC) is a wholly US agency, whose goal is: "make available so far as possible, to all the people of the United States, without discrimination on the basis of race, color, religion, national origin, or sex, rapid, efficient, Nationwide, and world-wide wire and radio communication services with adequate facilities at reasonable charges." (Five elected US politicians.) Whilst this organisation may have an International Bureau (IB) for agreed telecommunications bandwidths, there is clearly no provision to protect the interests of other countries - nor now seemingly even their own rights to freely explore and observe the vast universe. The contradiction is plainly obvious. e.g. What is truly ironic here is Musk's SpaceX laudable goals of advancing the exploring or colonising the Moon or Mars but willingness to sacrifice the ability and philosophical need to understand humanity's place in the world.
I personally find that the sheer degree of imposition of another country upon my own environment is quite repulsive and abhorrent. In my view, it is just another step towards the obliteration of our collective futures - as exhibited from such things as the dogmatic attitudes towards climate change or other unnecessary destructive human activities such as the ever continuing encroachment of light pollution.
IMO, the cost of this Starlink (and future satellite constellation 'infestations') on astronomy is far too high a price.

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December 7, 2019 at 9:14 pm

Even if it will be practical or even possible, who ruled that colonizing the Moon or Mars is a worth while or even moral laudable goal?

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December 6, 2019 at 9:52 pm

I’m glad they’re putting thought into reducing the satellites’ impact on the night sky... I wonder what effect, however, the black paint will have on the satellites’ ability to keep cool?

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December 7, 2019 at 1:06 pm

Are any other launch-capable countries planning similar exploits? If so, this could be just the tip of the iceberg (and just as destructive to astronomy as that one the Titanic encountered).

Doug Z

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December 10, 2019 at 2:04 pm

We have read in these pages recently of the negative effect of the relatively rapid switch from sodium vapor to bright-white LED streetlight and security illumination, and now the current debate over the Starlink situation. It all reminds me of something that Leslie Peltier once prophetically wrote over 50 years ago in Starlight Nights: " In these strange lights that cross the sky my two scopes see a gloomy portent, a distant early warning of the nights to come. Forty years ago, on the top of Mt. Wilson, the world's largest telescope could look down and see the gathering lights below. Today the approach is from above as well.

So much that man touches he destroys."

Monica, why was your article pulled so soon? I hope he hasn't gotten his fingers into S&T!!

Doug Z

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December 27, 2019 at 12:56 pm

I think that one of the best grassroots action that Sky & Telescope readers can take at this point is that they read, sign and share the petition that is trying to limit light pollution from space. It has been signed by over 6000 people, including many famous astronomers, astrophotographers and visual observers:

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