Ep. 601: Unexpected Light Pollution

Day by day, we’re losing our connection with the night sky. Already 1/3rd of humanity lives in so much light pollution that they can’t see the Milky Way without a drive. And now satellite constellations are adding additional light pollution, even in the darkest skies on Earth.

Show Notes | Transcript

Show Notes

NASA’s OSIRIS-REx Leaves its Mark on Asteroid Bennu (NASA)

The citizen scientists who helped map Bennu (Phys.org)

International Dark-Sky Association

Find a Dark Sky Place (IDA)

Light Pollution (IDA)

The Lost LED Revolution: Light Pollution is Increasing (Sky & Telescope)

Blue Sky (Hyperphysics)

RAS warns of growing light pollution as satellite fleets expand (Astronomy Now)

Satellites contribute significant light pollution to night skies (RAS)


Paranal Observatory (ESO)

La Silla Observatory (ESO)

ALMA Observatory

Cerro Tololo Inter-American Observatory (NOAO)

Radio Frequency Interference (NRAO)


Radio pollution of the OH 1612-Mhz band (adsabs)

Starship (SpaceX)

SpaceX Describes Exactly How They’re Planning to Make Starlink Satellites Less Visible From Earth (Universe Today)

Astronomers Confirm That Darksat is About Half as Bright as an Unpainted Starlink (Universe Today)

Starlink Satellites are Fainter Now — But Still Visible (Sky & Telescope)



United Nations

National Park Service


Transcriptions provided by GMR Transcription Services

Fraser:                         Astronomy Cast, Episode 601, Unexpected Light Pollution. Welcome to Astronomy Cast, our weekly facts-based journey to the cosmos where we help you understand not only what we know but how we know what we know.

                                    I’m Fraser Cain, publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hi, Pamela, how are you doing?

Pamela:                       I’m doing well. How are you doing Fraser?

Fraser:                         I’m doing very well. Have you seen the new pictures that NASA has sent back of Bennu of the landing spot of OSIRIS-REx?

Pamela:                       I had a really good laugh because they have this fabulous animation they did explaining what they intended to do with the mission, which is to basically fly down with their little arm and boop the asteroid, Bennu, and then fly away.

                                    The thing is that while, thereafter the fact, the interview still showed this nice friendly boop, in reality, Bennu punched really hard really, really hard.

Fraser:                         Yeah, yeah.

Pamela:                       And it was like on its way into the asteroid when thrusters were finally able to reverse its motion after it descended half a meter. That’s like more than knee-depth into the asteroid.

Fraser:                         Yeah. I’m just sort of imagining, like, it just sort of plunged its jaws into Bennu, took a giant bite, and then kicked itself back out. And now these new pictures that came out from NASA like the last day or two –

Pamela:                       Oh, yeah.

Fraser:                         – you can see this scar on the space rock where, you know, where it bit.

Pamela:                       Yeah, yeah.

Fraser:                         And yeah. It’s so cool. And it’s so exciting to sort of see this whole thing narrow it’s time for it to come home. But it is the capstone on this incredible work that everybody at CosmoQuest did to survey the asteroid, to mark every rock, to suggest places that it could land. The spacecraft did the landing. And now we see the proof. And now the data is – I guess the final step will be when the sample is in the hands of the scientists, and they’re actually examining it.

Pamela:                       Yeah. Instead of saying the film’s in the can; the rocks are in the can.

Fraser:                         Yeah. Absolutely.

Fraser:                         All the rocks, more rocks than anticipated.

Fraser:                         Yeah, yeah. Exactly, because it jammed its face half a meter into the asteroid, and it’s just overfilled, so.

Pamela:                       Yeah, yeah.

Fraser:                         Day-by-day, we’re losing our connection with the night sky. Already 1/3 of humanity lives in so much light pollution that they can’t see the Milky Way without a drive. And now satellite constellations are adding additional light pollution even in the darkest skies on Earth. And we will get into that topic in a second. But first, let’s have a break.

                                    And we’re back. So, can you see the Milky Way from your backyard, Pamela?

Pamela:                       I can, just not very dramatically. We have, unfortunately, those exact historic-looking, not actually historic, streetlights that the International Dark-Sky Association complains about where you have a pole with like a teardrop on top. And because they’re fake historic lights, they actually have really bright LEDs inside of them. And so, they make a fair amount of light pollution. So, even in my small town, we can see it. We just can’t see the details in it.

Fraser:                         It’s not bad for me. I can definitely see it from my backyard. But where I grew up, it’s much darker. But I can see the Milky Way. I can see fainter objects in the sky from my backyard. I can do some mediocre astronomy. And our town is maybe 25,000 people where I live. And so, but we’re surrounded by darkness. And so, I just have to go driving maybe 10, 15 minutes, and I get to much darker skies.

                                    But when you look at those dark sky maps for some people –

Pamela:                       Yeah.

Fraser:                         – who live, say, on the eastern seaboard of the United States or in Europe, there’s nowhere they can go –

Pamela:                       Right.

Fraser:                         – that isn’t half a day’s drive away that gets them to the place where they can actually start to see the Milky Way. It’s heartbreaking.

Pamela:                       And one of the things that makes it even more complicated is while a fair amount of attention has been paid to, well, streetlights like the one I have cause light pollution, lighting up historic buildings causes light pollution, all these things – gas stations. Gas stations are a terrible source of light pollution. If something attracts bugs, you’re probably generating light pollution.

Fraser:                         [Laughs] That’s a really good tip. Actually, we did a drive across the United States. And we got into Minnesota, and we stopped at like a road stop, you know, one of the rest stops. And the mosquitoes were just in giant clouds. You know, they would suck you dry in a moment –

Pamela:                       Yeah.

Fraser:                         – as you got out of your van. Yeah. It’s terrifying. And they’re all attracted – I’m sure they were attracted by the knowledge that human lights brings blood.

Pamela:                       Human warmth.

Fraser:                         But they’re also – and they’re fooled just by the light.

Pamela:                       Yeah.

Fraser:                         I think it’s the moon or something. Yeah, yeah. So, let’s start with, you know, the first thing that’s quite surprising, you know, we’re now living in the LED age. I don’t know about but you. I’ve swapped out all the lights in my house with LEDs.

Pamela:                       Yeah.

Fraser:                         I pay a fraction of the electricity bill that I used to. And the expectation was going to be that now that we had these new lights that would direct, you know, very direct illumination, be able to provide light exactly where you needed, that overall light pollution should be going down in our cities. But that’s not what happened.

Pamela:                       No. No. The problem is that LEDs tend to give off more light in the blue part of the spectrum. You can see that in how human beings look. We tend to not have that natural ruddy look we naturally have when we go outside under the sun. We instead look more like I do right now, kind of pale and with a slightly blueish cast. That’s from all of the blue light in the LEDs.

                                    And as it happens to work, the same fact that blue light scatters super easily that makes our sky blue, also means that all of those blue shades of light that are coming down from these low energy lights outside, it’s going to scatter off the pavement. It’s going to scatter off the cement. It’s going to go straight up and bounce around in our atmosphere, lighting that sky up and drowning the stars beyond.

Fraser:                         And so, what’s actually happening with the sky? How is the light interacting with the sky to cause this loss of the heavens for us?

Pamela:                       It’s an effect that’s called Rayleigh scattering, a lot of situations where, as all the different colors of light from the sun pass downwards towards the surface of the Earth, the particles in our atmosphere periodically get in the way. And the way scattering works, blue light gets scattered first, and then the thicker the atmosphere, the more particles in the atmosphere, the more colors of light are going to be scattered.

                                    So, when the sun is straight overhead, sunlight coming through, blue light scatters all over the place. And it keeps scattering. This is why you can look off at the horizon with the sun straight overhead, and you still see blue down at the horizon because light has just kept bouncing, and eventually, it bounces towards our eyeballs.

Fraser:                         Right, right.

Pamela:                       Now, as the sun gets lower towards the horizon, you’re looking through much more atmosphere. And that thicker atmosphere is able to scatter more colors of light, causing the sunset to be red. Now, when we’re looking at things in the other direction, light here on Earth will hopefully be directed towards the ground. And the ground’s going to absorb some of those colors of light, and it’s going to reflect some of those colors of light. The reflected light goes up, hits the atmosphere, and then scatters the same way the sunlight does. So, all that scattered light is creating the sky glow, a midnight sky that blocks stars and galaxies.

Fraser:                         And so, that Rayleigh scattering, we’re just seeing it in reverse. All right. We’re gonna continue this conversation in a second. But first, let’s have a break.

                                    And we’re back. And so, we can mitigate that light pollution a little bit, if we’re doing astronomy, using a special set of filters.

Pamela:                       Yes. So, luckily, LEDs, unlike the sun don’t give off their light in every single color of the electromagnetic spectrum. Depending on the chemistry involved in the LED, you get spikes in certain colors. And by combining those certain colors that we can create, thanks to chemistry, you get things that approximate different specific colors. I can make a light look red. It may be giving off light in a whole lot of different very narrow colors that my eyes perceive as red.

                                    Now creating filters that block out those specific colors native to LEDs is super useful if you’re trying to do astrophotography. It can be useful in some cases if you’re trying to do astronomy. But you’re essentially saying, these specific things I want to study, I’m not allowed to because their color happens to be coincidental with all the LED light that’s now polluting the atmosphere. So, ideally, we just want people to turn stuff off at night. Just turn it off, people.

Fraser:                         Yeah. And it’s like in order to get the same picture, or to get a good picture, you’re having to gather light for vastly longer periods of time. So, you’re throwing out the 99%, or whatever’s the amount of light, that is turning into light pollution. And then you’re just keeping that last little bit that’s the night sky. And then you’re trying to take pictures using that last little fraction of light because everything else has been ruined, by the moon too, I mean the moon or light pollution.

Pamela:                       Yeah.

Fraser:                         And so, you know, an interesting paper, I know, crossed both of our desks in the last couple of weeks. And this idea that in fact now it turns out that satellite constellations are starting to increase the amount of light pollution that we’re seeing. And this is bad because it’s everywhere, not just over the cities.

Pamela:                       And this is very much the same problem of just scattered light. It’s just the scatterers are much higher up. So, we have our satellites. They’re orbiting hundreds of miles above the surface of the planet, sometimes thousands, and because they’re higher up, they have a sightline to the sun that we may not have at the surface of the planet. So, sunlight comes over from behind the planet, hits this high altitude satellite, and that sunlight then gets reflected back toward us. And many of us have probably seen this when you go outside and you see these little faint points of light just zhzhzh across the sky. Today is the day I make sound effects while we record.

Fraser:                         That’s great. This is awesome.

Pamela:                       [Laughs] Now, while we’re used to seeing these individual satellites and being annoyed, I – all the research I did every third image – satellite.

Fraser:                         Yes.

Pamela:                       Satellite. And it’s getting worse because the numbers of satellites are increasing.

Fraser:                         Oh, yeah. Right now there’s, whatever, 1,000, plus another 1,500 Starlinks.

Pamela:                       Yeah.

Fraser:                         What are you going to do when it’s 40,000?

Pamela:                       Right. And so, we were fully aware of the problem created by these individual annoying streaks that passed in front of the things we’re trying to see and otherwise saturate our detectors. What I haven’t thought through, but in retrospect, is kind of obvious, as so often is the case, that light getting reflected back to us from the satellites, while some of it comes straight down and hits our eyeballs, our cameras, and things like that, a lot of the light, just like sunlight coming from the sun, gets scattered. And so, scattered light from satellites is brightening the sky. And that paper we read indicates it’s brightened it by 10%.

Fraser:                         The way I’d seen it was that it has the potential to brighten it by 10%. We haven’t hit 10% yet.

Pamela:                       Okay.

Fraser:                         But if the constellations reach the level that are being planned, it will essentially bring up the base level of light pollution across the entire planet by 10%.

Pamela:                       Yeah.

Fraser:                         And so, when you think about this situation, like, for the big observatories located in remote mountaintops in Chile, airplanes aren’t allowed to fly nearby them; you can’t build cities nearby them; there is no light pollution. You are in the darkest possible skies. But the satellites flying overhead are going to just add to the light pollution. There’s no getting away from it.

Pamela:                       So, this is the situation we’re in. And as bad as it is in optical, we’re also starting to hit radio difficulties. This isn’t entirely new. The first time we ran into this was with the GLONASS satellites used for satellite telephone communications. And because you want your satellite phone to work wherever you are on the planet, you ideally want to have more than one satellite overhead at any one moment. And you want all those satellites covering all of the planet from equator to pole. So, you need constellations.

                                    And once you’ve launched your satellites, no one can really stop what wavelength you’re working at. And there have been efforts made to protect the wavelengths of light that correspond to astronomically interesting sources.

Fraser:                         Interesting. I didn’t know that.

Pamela:                       Yeah. So, 1612 megahertz is one of those colors that attempts were made to protect so that we could better understand galaxies and stars and the chemical transitions that are possible. Quantum mechanics tells us exactly where to look. And it turns out that communication satellites said, “Uh-uh, Can’t.”

Fraser:                         Right.

Pamela:                       So, if you launch your satellites and use wavelengths you were told not to use, nothing can stop that.

Fraser:                         All right. Well, we’re going to talk about solutions in a second. But first, let’s have another break.

                                    And we’re back. So, what can be done? It is funny to me though that people – like, people are outraged, and I think rightly so, that that the night sky is being taken away from us. And I think the ad hoc answer is, let’s just build more space telescopes. But that’s not a solution.

Pamela:                       No. There was actually this fascinating image taken by the Hubble Space Telescope that caught a satellite at a higher orbit than it in one of its images.

Fraser:                         Right. I mean that won’t be the big problem.

Pamela:                       No.

Fraser:                         I mean if the satellites are orbiting below the space telescopes, it should be a solved problem.

Pamela:                       But there’s so many things you can’t do with space telescopes, like experiment and learn. Doing interferometry in space, we haven’t mastered that yet. All the things that we need to have massive telescopes capable of resolving the faintest and smallest objects in the sky, we’re not there yet. And sometimes you just want to experiment and tinker and try and do iterative design. And you can’t do iterative design with something in space. Not yet, not for a long time, even with Starship on the horizon.

Fraser:                         Right.

Pamela:                       So, we need to figure out how to fade our spacecraft.

Fraser:                         Yes. And fortunately, I think, SpaceX, with the Starlinks, they’ve been fairly responsive to the requests. Now, that didn’t stop them from deploying close to 2,000 satellites and then starting to come up with various ways to make them darker. But they are being responsive. So, what are the ideas that they’ve got?

Pamela:                       So, various ideas from changing the geometry, to changing how they align, to painting them, to using different materials. The idea is to reduce how much light can get scattered back down at the surface of the planet. And this is very much how you work on building stealth technology. It’s just instead of trying to hide from other nations, we’re just trying to hide from the sunlight, hide from the sunlight.

Fraser:                         Right. So, let’s talk about some of those ideas. So, one idea, as you say, you paint them black. They’ve tried that with some, and they call them DarkSat.

Pamela:                       Yeah.

Fraser:                         That worked. Didn’t work great. Definitely decreased the overall brightness by a little bit. They’ve also tried – they put a visor, they called VisorSat, that blocks – essentially blocks the sunlight from reflecting off the satellite. And that worked pretty well also.

Pamela:                       Yeah.

Fraser:                         I guess a lower altitude means that they spend less time in sunlight. And so, you’ve got the Starlinks, but they’re also brighter because they’re lower, as opposed to the OneWeb. So, Starlinks are lower, and then the OneWeb ones are far higher. And so, they’re dimmer, but they’re visible for the entire pass, and so they’re visible in the light of the telescope.

Pamela:                       Yeah. And one of the things that intrigues me is we’re seeing some experiments being done by other nations with things like ultra-black to see, can we create satellites that, in the wavelengths of light we care about, are transparent? Now, the thing with painting things black is they’re still giving off infrared light.

Fraser:                         Light, heat. Yeah. So, basically, yeah, you make the visual astronomers happy, but the infrared astronomers are miserable.

Pamela:                       And this is where we’re probably going to be looking at some sort of a combined answer to prevent the light pollution. They’re still going to block those things you’re trying to see. They’re still going to create problems with a lot of our astronomical images. But at least they won’t be making the background sky brighter.

Fraser:                         Yeah. And I mean if we could rewind the clock, and don’t get me wrong, I’ve wrong; I’ve got a Starlink. It’s awesome, right. It’s amazing.

Pamela:                       Yeah.

Fraser:                         And I can’t wait to be able to take that thing and put it in the car and drive to a remote location and do my work. I’m going to livestreams from the middle of the Canadian forest.

Pamela:                       Yeah.

Fraser:                         But I would have loved to have seen a conversation had between regulators and Starlink to say, let’s sit down, and let’s think through every single possible way that we could limit the impact that these are going to have on humanity, on science, on navigation, on future space debris. Let’s sort this out before we launch the satellites and not after.

Pamela:                       And as we’ve discussed before, this is a very complicated moral question.

Fraser:                         Yes.

Pamela:                       Because there are places where people’s economic and educational opportunities are limited by lack of affordable internet connectivity, from islands to remote places in the wilderness. You just can’t drop cables everywhere people happen to be.

Fraser:                         Yeah.

Pamela:                       But you can drop Starlinks.

Fraser:                         Yeah.

Pamela:                       And so, we are improving the economic and educational opportunities for millions, perhaps billions, of people.

Fraser:                         Yeah.

Pamela:                       And that’s an overall good. But how do we mitigate the cost?

Fraser:                         Yeah. At the very least, it’s an incredibly complicated conversation that needs to have been had that is sort of the future of humanity. But I think the thing that we can all agree on is that light pollution is already an enormous problem.

Pamela:                       Yes.

Fraser:                         And if you’re angry about the light pollution of satellites, you should be furious about the light pollution of the lighting systems that we talked about, the fact that already 1/3 of humanity can’t see the Milky Way, that the sky was already taken from us. And we did it – bit-by-bit, house-by-house, factory-by-factory – and have been doing it for the last 100 years. And there are many great organizations that are working to try to restore, protect these dark areas around the world.

                                    So, how can people get involved if they want to help protect the night sky?

Pamela:                       The flagship organization is the International Dark-Sky Association. They are working with the International Astronomical Union and the United Nations, as well as many National Park services to protect the places that are dark today, to keep them dark for tomorrow, and to work on mitigating, well, the impacts that we have from so many other things.

Fraser:                         Yeah. If you’re a member of local politics, work with your city to try to minimize – to change the way the outdoor lighting is done in your city. There are some cities – I guess Tucson, there are some cities that are doing it really well. If you have a house and you have external lights, think about it from the perspective of how much light is leaking up. Direct your lights. Don’t use lights that push in all directions. Don’t leave the –

Pamela:                       Motion sensors.

Fraser:                         Yeah. Don’t leave them up all night long. Just use them when you need them. Get involved, and really help fund some of these dark sky locations, and help protect some of these more pristine areas, and help raise awareness with other people that this needs to be protected. It’s like most people don’t even know what they’re missing. And it’s hard to get them excited or worked up about this thing that’s already been taken from them, which is kind of heartbreaking.

Pamela:                       Go out. Look up while you can. And try to build a future where you can see more than you see today.

Fraser:                         Right. Did you have some names for us this week?

Pamela:                       I do. So, as always, we are brought to you by our wonderful Patreons on patreon.com. So, today I would like to thank the following wonderful human beings who are part of what make this show possible, allow us to pay all the people who keep us in order. That’s Rich, Ali, Beth, Nancy, all of you. You’re out there herding us. And we are cats.

                                    All right. So, here’s our thanks to Adam Annis-Brown, cacoseraph, Ed of the Universe, Helge Bjørkhaug, Nicole Vorisek, Gordon Dewis, Bill Hamilton, Frank Tippin, Joshua Pierson, Thomas Sepstrup, Jack Mudge, Alexis, Richard Rivera, Sydnie Walker, Ben Lieberman, William Baker, William Andrews, Ron Thorrsen, Jeff Collings, Harald Bardenhagen, Marek Vydareny, Ben Floss, Jason Thomas, Arcticfox, The Lonely Sand Person, Nate Detwiler, Matt Rucker, David, Philip Walker, Elad Avron, Sarah Turnbull, Karthik Venkatraman, and Gregory Singleton.

                                    Thank you all so much. You make what we do possible.

Fraser:                         Thanks. Everybody. We’ll see you next week.

Pamela:                       Bye-bye, everyone.

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