Ep. 659: Clear Skies, Bright Satellites

Light pollution is a big problem, and it’s only getting worse — not just near cities but everywhere thanks to increased satellite constellations. How bad is the problem, and how can we fix it?

Download MP3 | Show Notes | Transcript

Show Notes

Universe Today (Patreon)

Universe Today

CosmoQuest (Patreon)

Find Your Night Sky Brightness on the Bortle Scale (Astro Backyard)

Starlink satellites can look like a plume or train of light (EarthSky)

Light pollution map

Light Pollution Map (Dark Site Finder)

One-Third of Humanity Can’t See the Milky Way (Astronomy)

Up with People

International Space Station (NASA)

Spot the Station (NASA)

United Nations


International Dark-Sky Association

UNESCO World Heritage Centre – World Heritage List (UNESCO)

Saving the night sky: New Zealand’s craziest experiment yet? (BBC Travel)

Aoraki Mackenzie (New Zealand) (IDSA)

Here’s why hut-hiking is the best way to see New Zealand (National Geographic)

The Lord of the Rings: The Fellowship of the Ring (Warner Bros.)

NIGHTS OVER TUCSON: How the Tucson, Arizona, LED Conversion Improved the Quality of the Night (IDSA)

Bright LEDs could spell the end of dark skies https://www.energy.gov/eere/ssl/potential-impacts-led-street-lighting-sky-glow (MIT)

LED streetlights are increasing blue-light pollution in Europe (Physics World)


Amazon reserves up to 83 launches for Project Kuiper satellites (GeekWire)

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

Apparent Magnitude (Swinburne University)

Skyglow (Wikipedia)

Coruscant (Wookiepedia)

Star Trek

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Transcriptions provided by GMR Transcription Services

Fraser: Astronomy Cast, Episode 659 “Clear Skies and Bright Satellites”. Welcome to Astronomy Cast, your weekly facts-based journey through 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. I have been a space and astronomy journalist for over 20 years. And with me is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey, Pamela. How are you doing?

Dr. Gay: I am doing well. I want to apologize to our audience if today’s quality isn’t what you are used to. One of our team members, Annie Wilson, is getting married this week and all of us are in Vegas to celebrate. So, I’m coming to you from hotel internet, which is not the best. But the show will go on.

Fraser: So, you might not know but every time a person signs up as a patron to Universe Today, I send them an email asking them to do an interview with me. And it’s actually talking to me like we’re at a Zoom meeting and I’m asking you a bunch of questions about where you found Universe Today and so on. And I would say about half of the people first found out about Universe Today through Astronomy Cast

Dr. Gay: Wow.

Fraser: So, for those of you who have sort of followed this journey from Astronomy Cast to Universe Today, thank you. I really appreciate it. For those of you who don’t realize, it’s so funny. Every episode I go, “I’m the publisher of Universe Today.” And people are like, “I didn’t realize that you did Universe Today or what this Universe Today thing was.” So, maybe I need to say, “Universe Today” 10 times a show or something. I don’t know. But it’s been very interesting to have this conversation with people. So, just a secret bonus if you didn’t know, if you sign up for my Patreon over at patreon.com/universetoday, I will ask you to talk to me. And it will actually be me and we will actually talk.

Dr. Gay: That’s amazing.

Fraser: Right. 

Dr. Gay: I need to start doing that for CosmoQuest, I think. That’s amazing. I –

Fraser: It is so much fun.

Dr. Gay: – love that idea.

Fraser: It’s so much fun. And after you see all these trolls, all these nasty people out there on the internet, people yelling and fighting each other, and you just get like 15 minutes of pure bliss talking to people about interesting things. And it just restores your faith in humanity. Anyone who does run a Patreon, talk to your fans. It’s so much fun. Now, light pollution is a big problem and it’s only getting worse; not just your cities, but everywhere thanks to increased satellite constellations. How bad is the problem and how can we fix it? So, you’re right now traveling. You’re in Las Vegas. What Bortle number would you give the place?

Dr. Gay: Oh, man. How bad does it go? It’s not quite Times Square or that intersection in Tokyo with the crazy crosswalks, but there’s not a lot of stars up there or planets. It’s just kind of a few things. And for better or worse, unless there’s a Starlink train going over where I am right now, you’re not even gonna see the satellites because of all those lights pointed up on the buildings, pointed down on the ground that are scattering into the sky.

Fraser: And actually, Vegas is an island of light pollution in an ocean of pretty dark skies in the West side of the United States. Like, if you look at a map of the light pollution in the U.S., there is this clear line between the West and the East. The East is a nightmare. It’s funny. So, I talk to people about how to find dark skies, and so I pull of the dark sky finder map which overlays light pollution on top of Google Maps. And you can sort of zip around and look at various places, and I’m looking for stuff that is green. The best you can have is black. Then, after that is blue, and then green. Green lets you see the Milky Way. If you’re in green, you can see the Milky Way.

                                    And for people on the West side, it’s easy. You just go in any direction for about 10 minutes and you should be able to see the Milky Way. For people in the East, it can be an hour to get somewhere, two hours to get somewhere where they can actually see the Milky Way. And for people in Europe there’s nowhere you can go. Get on a boat and –

Dr. Gay: Oh, you can’t really. In Portugal, there’s this dark sky site. In Spain, there’s a dark sky site. But they’re not dark the way we’re used to dark here.

Fraser: And so, if you’re in, say, the Netherlands, I don’t know. The Alps? There’s just nowhere to go. It’s terrifying. And I think a third of humanity now can’t see the Milky Way.

Dr. Gay: What is the darkest place you think you’ve ever been?

Fraser: Australia, no question. By far. Hands down.

Dr. Gay: For me, and this is so bitter sweet in these times that we live in, back when I was in high school, I was in the People-to-People Youth Exchange. And a whole group of us astronomy nerds went to U.S.S.R to be at an exchange at their six-meter telescope, which at the time was the largest in the world. And as part of the exchange, they took us camping up on the glacier, or near a glacier. We were in the rock field at the base of the glacier.

Fraser: Wow. 

Dr. Gay: And being a moody, slightly-goth-in-my-head-but-never-had-the-willpower-to-do-the-makeup kid, I decided one night I was going to go off by myself and sit on a rock and just stare at the stars. And that was the first time in my life I’d ever seen a satellite. And to me, it was this magical moment of figuring out “Wait, that moving thing is not an airplane,” and just folding into the sky and seeing all these things I’d never seen before; being completely lost because there were too many stars for me to easily find my way around. And I’d grown up desperately trying to find Andromeda from my driveway in New England and that was not a thing that I ever succeeded at. To go from that to this dark satellite was amazing.

Fraser: So, growing up, there had always been satellites overhead and my dad would teach me to find them as we’d go out at night. And I guess being in Canada, we’re farther north and so when we’re in the summer in Canada, then the satellites are in sunlight for longer than they would be for more southern latitudes. And so, during the summer you can be sitting out in the warm evening and just watch these satellites go overhead. We can get three passes of the International Space Station in the summer 90 minutes apart, separated –

Dr. Gay: Wow.

Fraser: – in different spots in the sky. And we definitely get Starlink trains as they’re going by. So, I think this idea of dark skies and the light pollution, it’s been around for a long time. It’s been around for probably 50, 75 years. It’s been around for a long time and it’s just been getting worse and worse. What is the state of light pollution today?

Dr. Gay: There are United Nations committees working in concert with the International Astronomical Union and the International Dark Skies Association, IDA, to try and identify places in all the nations of the world. And they’re not gonna succeed in all the nations, but trying to find places where the skies still allow you to see Andromeda with your unaided eye, still allow you to make out Messier objects easily, and take those sites with a visual magnitude of getting down to six if your eyes are good, seven if you’re a crazy eye person. Some people can do that. I learned that and it was shocking. 

                                    They’re trying to find those places and turn them not just into national parks but into internationally recognized dark sites, the same way we have UNESCO historical sites. Now, we’re starting to have essentially the equivalent for dark places. And this is in recognition of if we don’t set aside the places that are dark, we’re gonna lose them forever; the same way one might once have set aside national parks to be preserves of animals, now we’re preserving the sky as well as the landscape.

Fraser: I don’t know if you had heard the news but New Zealand is thinking of trying to make the whole country a dark-sky preserve.

Dr. Gay: That would be amazing. There’s already a dark site not too far away from Christchurch. And I haven’t been to that half of New Zealand, but there are more sheep by orders of magnitude in New Zealand than humans and it is a place that celebrates its countryside. You can actually hike all the way from the southernmost tip of the islands, take a ferry to get between the two islands, and then walk the rest of the way with little cabins for hikers all along the way. It is designed to allow people to celebrate the landscape, which is why Lord of the Rings could so successfully be filmed there. 

                                    And it’s easy to preserve the sky if you don’t have a lot of people and you say, “Okay, when the people do start encroaching on this land, we’re going to require that constructions of new properties be built in such a way that we’re not taking away from our ability to see this sky.

Fraser: There are some places that are demonstrating that this is completely feasible. You look at Tucson, Arizona, which is near a lot of the observatories, and the whole place is designed with a respect for the night sky. The lights point down; they’re dimmish, and any excessive lights being sent up into the sky is discouraged. And you can still get around at night in Tucson, and yet you have these skies that let you see the Milky Way pretty much when you’re in any part of the city. And so, it’s not impossible. And I think we expected that, as the new revolution in the LED lights came out, their lower power but same amount of light, plus their ability to be pointed a lot better, would turn the tide of light pollution. 

                                    But it didn’t happen. If anything, it got worse. They just said, “Okay. Well, with more power we can put out more light, so let’s put out more light.” So, they swapped out dimmer light fixtures with brighter light fixtures. So, actually the light pollution problem is getting a lot worse in a lot of cities. 

Dr. Gay: And bluer. That is an unexpected outcome because different colors of light reflect in different ways, scatter in different ways. And as many of us have encountered it’s super easy to get a bunch of super-bright, on-the-blue-side-of-the-spectrum LED lights and just create motion sensors and floodlights. And I know that I currently have six extremely bright LED lights with solar panels on them in my front yard because they were pointed at Halloween decorations. Now, they will eventually come down. Although, we’ve decided the skeleton in the tree is gonna get a Santa hat and he stays there. But when you get to the –

Fraser: Right.

Dr. Gay: – point that you can get a solar-powered, very blue LED light, you can no longer make energy arguments.

Fraser: Right, right. So, let’s talk about the satellite problem. And obviously, at this point, there are various companies, especially SpaceX with Starlink, they’re adding hundreds if not thousands of satellites every year. We’re up to, I think, like 3,000, almost 4,000 Starlinks and they’re planning to get to 42,000 satellites. Amazon is planning to do its version. So, what impact are these satellite networks going to have on light pollution?

Dr. Gay: What we’re running into is these satellites are typically in low Earth orbit so that you can have low latency connections. Not that this particular connection feels all that low latency.

Fraser: Right. I’m on Starlink right now.

Dr. Gay: And I’m on hotel, so I have no idea what it’s using. But these low latency connections require satellites that are closer to the planet, and because they’re closer to the planet they’re able to appear brighter. So, what’s happening is, when light hits a surface, if it’s a perfectly smooth surface, the angle that the light comes in equals the angle that the light comes out. And in that scenario, you end up with super-bright satellites because the light can get beamed back. Now, luckily, perfectly reflected surfaces aren’t really a thing. So, in general what we’re looking at is sunlight hits a satellite, scatters out in all directions due to the roughness of the surface, and then we have a one-over-distance-squared relationship between us and how bright that satellite appears. 

                                    Now, if something gets fainter as the square of the distance, if you double the distance, it’s going to be four times fainter. Now, on the other side, if you bring it closer it’s gonna be all that much more bright. All these satellites in low Earth orbit are substantially brighter than the ones that are in geosynchronous orbit many, many, many times higher up.

Fraser: Right, right. 

Dr. Gay: So, there’s that factor.

Fraser: There was some interesting research that I was looking into. Astronomers have been very carefully measuring the brightness of the Starlinks and without any kind of brightness mitigation features. They’re about 6.5 magnitude; so, beyond the ability of most people, even in the darkest skies, to be able to see –

Dr. Gay: Once they get to their final orbit.

Fraser: – once they get to their final orbit. When they’re going up there in a train, they’re very bright and many people have seen that. Once they get to their final orbit, they’re essentially impossible to see with the unaided eye. There’s the VISORSat version which it looks like they’ve abandoned which get it even darker; I think it’s like magnitude 7.5, which is beyond the eyesight of anybody. There’s also ones they painted, which are like 6.8, something like that. So, they’re all in the 6.5 to 7.5 magnitude range which you need a pair of binoculars to be able to see them. And so, I think that great worry that you would stand outside and you would see this grid of satellites orbiting around planet Earth all the time wasn’t warranted. 

                                    But there absolutely has been an impact on astronomy, or it is beginning now and we’re starting to really recognize what the true ramifications of this are. What’s the impact?

Dr. Gay: What we’re seeing is it is getting significantly more difficult to take long exposures where you don’t have a satellite passing over one or more of the optics that you’re interested in. So, say that you’re looking at a galaxy cluster. Well, if you get a Starlink satellite passing right over the galaxies you’re interested in, that’s no longer data you can use. So, you have to take more exposures to get the same amount of un-interfered with photons from the galaxies. So, if 1 in every 10 images is going to have a satellite knocking out an object in your busy galaxy cluster field, that’s going to end up increasing by 10 percent how many images you have to take. 

                                    It’s not actually that bad. It’s just back-of-the-envelope math. But it’s going to have a multiple percentage impact as near as we can tell right now. And while we don’t have a grid orbiting out planet, I went camping during the summer and was shocked at the number of satellites that are now in the early evening sky. Luckily, it does mostly impact, for mid-latitudes, the early evening and the hours before dawn. So, that if you’re out all night observing with your eyes during a meteor shower, you can tell when the sun is gonna come up because the number of satellites gets higher again.

Fraser: I think it’s really important to clarify the problem because the satellites are only visible when the satellite is illuminated when the Earth is in shadow. So, when it’s nighttime, you still need to have the satellite illuminated and that only occurs just after sunset and just before sunrise, and in regions that are relatively close to the horizon, which are typically fairly terrible places to point your telescope anyway. You wanna point your telescope straight up to go through the minimal amount of atmosphere.

Dr. Gay: You can get satellites straight overhead though, just to be clear. It all depends on the orbit they’re in and how high up they are. The wild thing is that –

Fraser: And where you are. 

Dr. Gay: – the higher up, the more you see them.

Fraser: So, if you’re in Canada, which has a fairly high latitude, then you’re closer to the pole and there’s a much better chance that sunlight in the summertime is gonna be peeking over the top of the planet for hours. And that’s why I was mentioning before the show we could see the International Space Station on multiple passes because the sunlight is essentially going overtop of planet Earth while Earth where we are is in shadow. But you –

Dr. Gay: Right.

Fraser: – get the same problem in the Southern Hemisphere in places like Chile where all the big telescopes in the world are. They are closer to the South Pole and they have the same problem. So, it also really matters with the searches for, say, dangerous asteroids which are caught in the glow of the sun. You have to search for them near the horizon, near the sun shortly after sunset, shortly before sunrise. That’s the only time that you can find these potentially planet-killing asteroids, and that’s a problem. But one other problem is just the increased skyglow. And I think this was kinda unexpected. Can you talk about that?

Dr. Gay: Yes. So, you have two different things going on. So, first of all you have the specific light coming off of the satellite that allows you to see that bright streak through your image. But as I was saying, the light reflected off of satellites that have a rough surface, it’s coming out in an expanding cone, assuming flat surface. There’s lots of geometry involved. That light coming through the atmosphere is then getting scattered around by the molecules and atoms in our atmosphere. And so, just like sunlight gets scattered to create the blue light we see during the day as our blue sky, the scattered light coming off of the satellites is causing not a blue sky our eyes can see but a change in how dark the sky appears to a telescope because of all that scattered light within the atmosphere, even in the night.

Fraser: And so, you’re getting light pollution over top of these observatories, even though they’re far away from any city –

Dr. Gay: Right.

Fraser: – any artificial lights because now these satellites are everywhere. And this problem is just starting to appear, but it’s going to get worse and worse and worse as there are more satellites in the sky.

Dr. Gay: It’s something where I often find myself asking “Do you want to be on Coruscant? This is how we get Coruscant.” And while –

Fraser: Right.

Dr. Gay: – they have flying cars more at the skyscraper height, this zipping around of satellites in low-Earth orbit is going to eventually create a world that looks like it has a swarm of gnats flying around it to not-too-distant space explorers.

Fraser: I think about Star Trek. You see the giant shipyards and dock facilities and you think, “Boy, what would be the light pollution of that thing?” Right? It would just be this gigantic, gleaming object that would be visible and casting shadows, and it would be like the full moon every night every time this thing passed overhead. It’s the downsides you don’t think of when you’re excited about your Star Trek future.

Dr. Gay: One crazy calculation I ran preparing for the show that we will eventually record, I promise: when we were figuring out different things to calculate, I calculated how big would the International Space Station appear if it was at geostationary orbit. Right now, someone with a really good 14-inch or larger telescope on the planet has the ability to resolve out the solar panels and the basic shape of the International Space Station because it’s in low-Earth orbit.

Fraser: They’ve seen astronauts spacewalking.

Dr. Gay: Right. Now, if you boost the International Space Station all the way up to geostationary orbit, it’s about an arc second across. So, if you build your shipyard out at greater than geostationary distances, you would have this pinprick of stupidly bright like Venus moving through the sky. And I love this idea that something that’s so big could appear so small from the surface of the world. But reality is, they’ll probably put it a whole lot lower down. You can imagine in our sci-fi fantasy future putting it actually at geostationary so that you can do a space elevator. The future’s gonna get weird for the next three generations, assuming we don’t kill our planet. So, Star Trek, please.

Fraser: Right. 

Dr. Gay: Please, now.

Fraser: So, what can be done? Because we’ve had this conversation before that, on the one hand, satellite internet has the potential to provide high-speed internet access to a huge portion of humanity. And on the other side, the price that we’re gonna pay is a loss to ground-based telescopes. What can be done to solve this problem at least to some degree?

Dr. Gay: So, the shape of the satellite matters a lot in how much light it’s able to reflect back down to the planet. So, if you can change the profile so that the smallest possible surface area is facing our planet, that will help. Having rough surfaces helps. Having surfaces that don’t reflect easily helps because at that point you start getting into the infrared because if it doesn’t reflect light well, it’s going to warm up.

Fraser: Right. Then, it heats up. Right, or reflects radio waves. So, I think the most important thing in the short term is to provide real-time telemetry information to the telescopes, to the observatories. So, right now, there is no schedule for when various satellites are gonna be at various locations, and yet it should be. In fact, people have started to try and make this, but this is something that should just be supplied by the satellite operators and should be part of if you want a license, you have to provide real-time, down-to-the-nanosecond information about where your satellites are. 

                                    And so, then you integrate that with the giant observatories, and then they know that they can take pictures and pause for one second while the satellite is gonna more through the object that they’re attempting to image. It doesn’t have to be the whole field of view. If they’re just trying to get one little galaxy cluster, if you just wait a second before you start your observation run and you will then get the data that you need. This should be possible and this should have been mandated. And I can’t believe that we’re at this place where the telescopes aren’t getting real-time information about the satellites that they can then adjust. The classic example is the machine guns that timed, so they don’t shoot the propellors of the of the airplanes. You can just –

Dr. Gay: I love that.

Fraser: – time everything. That would be useful just in general across all observatories and you would get back pretty much all of the lost time from the satellites passing through your data. You won’t get back the skyglow, and there’s kinda –

Dr. Gay: Right.

Fraser: – no place to hide from that. And obviously people are gonna say, “Well, just go to space,” but ground-based telescopes have their place in modern –

Dr. Gay: Right.

Fraser: – science. And so, we can’t just say, “Hey, let’s turn everything into space.” They have to work together, and I think they should have put mandates, made requirements, and we would be in a totally different place with a much better partnership between science and internet satellite providers.

Dr. Gay: Right. The one type of device that we just aren’t yet to a point of being able to put in orbit at all is the giant spectrographs that we used to get detailed analysis of the composition of fairly bright objects. These spectrographs are often the size of a basement underneath an observatory where equipment is very carefully put together, where that light is moving tens of meters around in all of its forays to eventually land on the detector spread out into that perfect rainbow we can analyze. Those require tweaking, they require trial and error to get everything absolutely perfect, and I don’t want to even try to imagine doing all of the optical bench alignments that are necessary with building something like that in space at this point in our development of human construction and on orbit. 

Fraser: So, fix your house. Fix your streetlights. Fix your country to give us back that night sky and try to figure out how to bring balance to our need to light our environment, to communicate with each other and our ability to explore the universe. They can co-exist. People just have to make this a priority. It’s an environment like any other and let’s stop trashing it. Thanks, Pamela.

Dr. Gay: Exactly. Thank you, Fraser. All right. So, I have a whole lot of people to thank this week. This week I would like to thank William E. Kraus, Matthias Heyden, Claudia Mastroianni, Jeff Willson, Cooper, Gregory Singleton, Tim McMackin, Kenneth Ryan, Alex Raine, Eran Segev, Allan Mohn, Paul D. Disney, Micheal Regan, NinjaNick, Scott Briggs, Benjamin Müller, Steven Shewalter, Michelle Cullen, Janelle aka Veronica_Cure, Omar Del Rivero, Dean McDaniel, Don Mundis, Peter, J. AlexAnderson, Matt Rucker, Benjamin Carryer, Jim McGihon, Anitusar, Mark Steven Rasnake, Moose and Deer. 

                                    Abraham Cottrill, Mark H. Widick, Philip Grand, Father Prax, schercm, Frode Tennebø, Bruce Amazeen, Dustin A. Ruoff, Paul L. Hayden, Gfour184, Sean Martz, Andrew Stephenson, planetar, Gabriel Gauffin, Steven Coffey, Cemanski, Glenn McDavid, Dwight Illk, Karthik Venkatraman, Brent Kreinop, Sam Brooks and his Mom, thank you. James Rodger, The Mysterious Mark, john öiseth, John Drake, Camy Raissian, Nate Detwiler, The Air Major. Thank you all. You allow us to do what we do which, weeks like this, are going to require a lot of our editing team. So, thank you for –

Fraser: Right.

Dr. Gay: – fueling our editing team.

Fraser: Thanks everybody and we’ll see you next week.

Dr. Gay: Bye-bye. Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a Creative Commons attribution license. So, love it, share, and remix it, but please, credit to our hosts, Fraser Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website: astronomycast.com. This episode was brought to you thanks to our generous patrons on Patreon. If you want help keep this show going, please consider joining our community at patreon.com/astronomycast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your Inbox and invites to online events. 

                                    We are so grateful to all of you who have joined our Patreon community. Anyways, keep looking up. This has been Astronomy Cast.

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