Daniel and Kelly’s Extraordinary Universe - What is tidal locking?

Episode Date: May 25, 2023

Daniel and Kelly talk about how the gravitational dance of the Earth and Moon, and other objects in and out of our Solar System.See omnystudio.com/listener for privacy information.

This is an I-Heart podcast. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System

On the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want or gone.

Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Do we really need another podcast with a condescending finance brof trying to tell us how to spend our own money? No thank you. Instead, check out Brown Ambition. Each week, I, your host, Mandy Money, gives you real talk, real advice with a heavy dose of eye. feel uses, like on Fridays when I take your questions for the BAQA. Whether you're trying to invest for your future,

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No, I didn't audition. I haven't auditioned in like over 25 years. Oh, wow. That's a real G-talk right there. Oh, yeah. We'll talk about all that's viral and trending with a little bit of cheesement and a whole lot of laughs. And of course, the great bevras you've come to expect.

Listen to the new season of Dacias Come Again on the I-Heart Radio app, Apple Podcast, or wherever you get your podcast. Hey, Kelly, I have a controversial question for you. Oh, boy. Coming from you, that makes me particularly nervous? Is this another episode I'm going to have to make sure my kids don't listen to? No, but it might cause some other kind of family drama.

Okay, now you have my attention. Well, you know, since you're married to a cartoonist, I'm wondering if I'm allowed to ask you whether you're a fan of a different cartoon. Well, that depends if it's a rival cartoon or not. So I'm wondering if you have a favorite cartoon from The Far Side. Oh, I mean, he hasn't updated for a while, right? I mean, I suppose he's still competition. But anyway, all right, let's see, let's see.

So hard to pick so many favorites. So there's one where there's a slide, you know, like a kid's playground, and some spiders have built a net or a web along the bottom. And one spider is saying something like, if we can pull this off, will never be hungry again or something like that. And I, as an invert person, just thought that was amazing. And, of course, I liked the, like, school for the gifted, the one that, like, was on T-shirts when I was a kid.

What about you? Well, I have to ask you, do you see that spiders eating a baby cartoon differently now that you're a parent? No, still hilarious. Still hilarious. Still hilarious. I think your children should be terrified if they listen to this episode. Probably.

Oh, my gosh. Poor kid won. The other day I told her to go get a bowl in my office and she thought it was going to have something like candy in it, but she accidentally picked up the bowl of dead insects that I found in the barn that I was thinking of pinning at some point. And they were all over my office. So she must have seen it and thrown it up in the air. And they went all over. My kids are going to have very high therapy bills at some point.

But I love them very much. I think that living your house must be even weirder than the far side cartoon. Almost certain. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I don't think I've yet traumatized my children with insects. Hi, I'm Kelly Weiner-Smith, and I study creepy-crawly things at Race University. and I'm traumatizing kids all the time.

Education through trauma. Is that your strategy? That's a good way to make people remember stuff. Well, you live out on the farm where there's lots of access to creepy, cruelly, weird things. And so I hope your kids are becoming acclimatized to that. I'm making them tough. Because it takes a brave soul to explore the nature of the universe or even just your backyard, depending on what's slithering out there.

So whether or not you turn your eyes down to the ground or up to the sky, eyes is a whole lot of stuff to wonder about. And so welcome to the podcast, Daniel and Jorge explain the universe in which we do all of that wondering. We think about everything that's between your toes and everything that your eyes can gather as you look up into the night sky. We think about what's on the moon, what's on the back side of the moon, and what's in the deepest, darkest depths of the universe. We chew all of it up and try to digest it and explain it to you. And it's not always pretty. Sometimes the truth is just gross. My Typical co-host and friend Jorge Champ can't be here today.

So I'm very glad to have one of our regular guest host, Kelly. Kelly, thanks very much for joining us again and terrifying your children. Yeah, well, I hope I could terrify some people today, too. Thanks for having me back. But today we're not talking about the weird, creepy, crawly bits that are inside Kelly's pantry, strange as that might be. We are turning our eyes to the sky tonight. We are thinking about what's out there in the universe and what we can see and what we can can't see and how the gravitational forces that have built the structure of our universe also limit

what we can see out there. If you were a kid like me, then you spend a lot of time looking up at the night sky, not just absorbing the stars, but also gazing on the closest object that's out there, the biggest, fattest thing in the night sky. And that's, of course, our moon. It has so many fascinating features to it. But one of the most interesting features is that you always see the same features. Kelly, do you remember understanding this as a kid, or wondering about why you're always seeing the same bits on the moon? You know, I really wish you hadn't asked me that because the answer is when I was a kid, I didn't realize I was always seeing the same side of the moon that hadn't really hit me

until I think maybe I was in college and then I was like, wait a minute. And I guess I just wasn't, I was looking down at the salamanders and not up at the sky. But so no, that that is not a question I had when I was a kid, but it should be. When did you learn this? I remember learning about it, I think, when I was seven or eight. But, you know, my dad was pretty into astronomy and into science. And so we talked about this kind of stuff. Something I'm still curious about, though, is when humanity understood that or when

humanity understood, it was an interesting question. Like the ancient Chinese astronomers who spent a lot of time looking up at the moon and predicting its eclipses, did they figure out that the moon was a sphere and that it was rotating and that it was weird that we always saw the same side of it? Or is this just something they overlooked? Do you know the answer to that question? I don't know the answer to that question. I've been digging through the history of astronomy a little bit.

And I know that Newton understood it because of his ideas about gravitation. But digging deeper into history, it's not really discussed very much. And I sort of wonder if people suspected that it was just a coincidence that the moon rotates at this perfect rate just so that we can only see one side of it. Because, you know, there are other fascinating coincidences about the moon. For example, the moon and the sun happen to be the same size in our sky, right? The sun is much, much bigger, but much, much further away. And those two numbers line up perfectly. So the sun and the moon appear to be the same size, which is why we can get so many fascinating eclipse effects.

And that, of course, is just a coincidence. There's no, like, deep reason for that. It just happens to be these two numbers just kind of line up in our universe. And humans are notoriously tripped up by coincidence. is exactly and so I think ancient astronomers must have wondered about that size and I wonder if they also wondered about the rotation of the moon if they understood that now I do know that ancient Chinese astronomers had a little bit of a disadvantage compared to for example ancient Greek astronomers because they didn't have geometry right we think about the universe in terms of geometry you imagine how eclipse has happened and you think probably in your head you have a mental picture of all these things happening and to explain it but Chinese astronomers didn't develop geometry, so they didn't have the same sort of geometrical thinking that we're all very familiar with. Instead, they had like tables of numbers and they had arithmetic and they can manipulate these numbers to do their predictions. So I think they must have thought about these things very

differently than we did. Interesting. It's nice to have our modern tools. Thank you to those folks who invented geometry. Turns out to be pretty useful. Quote unquote modern. Yeah, right. And so we have been looking up into the night sky and looking at the moon and seeing the same side of it for a thousands and thousands of years. And now, of course, we understand why. And so today on the podcast, we're going to be digging into the physics of the far side of the moon and many other objects in our solar system that exhibit the same behavior. On today's episode, we'll answer the question.

What is tidal locking? And this is another thing that connects us to the dinosaurs, right? Because they also would have seen the same side of the moon. If dinosaur geometers had figured that out, boy, well, they could have written a paper and got a lot of citations. They really could have. And then maybe they could have started a, you know, NASA and had an asteroid deflection program. Everything could have been different. You sound like you're kind of hoping for that, but, you know, in that scenario, we don't exist.

Oh, good point. We're rooting for the asteroid on that one. That's right. We sure are. I'm sorry, dinosaurs. Which puts us on the anti-math education for dinosaurs committee as well. It's an uncomfortable place to be, but no, it doesn't feel very good, but I'm firmly in this position, yeah. So this is a topic that affects our moon and affects our planet and affects a lot of things in the solar system and in other solar system.

It's a fascinating little bit of physics. So I was curious what people knew about the topic of tidal locking and if they understood the physics of it. So I went out there into the internet to ask folks if they understood this. Thanks very much to those of you who participate in this segment of the podcast to let us know what people think. about the topic of the day if you'd like to hear your voice for a future episode please don't be shy write to me to questions at daniel anhorpe.com so think about for a minute do you understand the physics of tidal locking here's what some listeners had to say so i believe that tidal walking is when a say a planet has a moon that's locked in orbit at a

certain distance so the tides are always the same so i guess you could say that we're in tidal locking because day in and day out our tides go the same because the moon's in a fixed orbit. Tidal locking is just like our moon. We see the same face of it at all times. It has no spin and the dark side of the moon is facing outward. It is the deformation that a celestial body suffers when it's orbiting or is orbited by another massive celestial body. Tidal locking is when a lower mass body is orbiting a much higher. mass body, and the same side always faces it. So I know that we always see the same side of a moon. Moons tidily locked to the earth. I was impressed that none of the listeners seemed totally stumped by this, because I feel like title locking is not necessarily something that you hear.

Like that, at least is a phrase I don't hear very often. And so, like, it seems like some people knew exactly what you were asking about. And none of them were like me when I was a kid and we're just Totally unaware that this is a thing that was happening. Yeah, we got some pretty well-educated listeners. The word tidal, I think, makes some people think of tides, which is connected, of course, to tidal forces, you know, like the moon pulls on the earth and squishes its oceans and makes us have higher tides in some places

and lower tides and other places. But that's not what we mean by tidal locking. Tidal locking is actually a different phenomena we're going to dig into today. But thank you very much to all of our volunteers. we really cherish your thoughts. Yeah, you have a smarter than average audience, I think, or a smarter than Kelly average audience. I'm always impressed by the answers.

They're smart and they're good looking too. That's right. I think that's called the Halo effect. You know one good thing about them and you assume you know all the good things about them. So let's dig into the physics of tidal locking. What it is, what's going on and why it plays such a big role

in what we see in our night sky. And I think the first thing to understand And it's just like the geometry of what's going on. Obviously, the moon is orbiting the earth and the earth is spinning. And the moon is spinning around the earth. And the moon is also spinning on its axis. So there's sort of a lot of spinning going on. But you've got to get all that spinning in your head to understand like why we only see

one side of the moon. Yes. So I am staring directly ahead trying to picture everything. So go ahead. What should I be imagining? So first just put yourself on the earth. and forget the fact that the earth is spinning and just move the moon around the earth in your mind. And imagine the moon is like a shoe or something.

If the moon is not spinning, it's just orbiting the earth, then the earth is going to see different sides of the shoe. It's going to see the back of the shoe. It's going to see the front of the shoe. Because as the shoe moves around the earth, different sides of it are going to be closer to the earth or closer to outer space. So the shoe is not rotating either? That's right. So first the shoe is not rotating. And so we see one side of it and then we see the other side of it.

So if the shoe or the moon or whatever is not spinning, then you would see different sides of it, right? Now, the moon, of course, is spinning. It's spinning on its axis. But if it was spinning at some random rate, like really, really fast or really, really slow, you would still see both sides of it because eventually it would spin it a way that revealed every part of the moon. The only way for us to not be able to see part of the moon is for its spin to be perfectly synced up with its orbit. So that as it goes around the Earth, it turns just the right. amount every second so the same side of it is always facing the earth like if the back side of the

shoe is always facing the earth because the shoe itself is spinning at just the right rate as it goes around the earth and everyone on every part of the earth is always seeing the same side of the moon right it's not like you know in the u.s you see one side and in china you see the other side or right you're always seeing the same side that's right the same side of the moon is always closer to the earth and the other side of the moon that we call the far side which i assume is the origin of the name of the far side comic is always facing outer space and this is the sort of coincidence we were talking about like these two numbers the rate at which the moon goes around the earth and the rate at which the moon spins around its axis have to be perfectly

synced up to get this effect and why are they perfectly synced up is this one of the few instances in which we have something special going on and they just happen to sink up or are we just like every other moon because this happens all the time so it's not that special and it's not a coincidence but it's not something that's always happened like to really get into it you have to understand the history of the formation of the moon like how did it get made how was it spinning originally and then how has that changed you know our moon is not just like some object that we captured as it was flying by we think that the moon actually comes from a huge collision something like a hundred million years after the earth was formed. So we're talking like 4.4 billion years ago. You have some

like very hot proto earth. It got slammed into by some giant Mars size planet they call Thia. And so you're talking about a huge collision like Earth versus Mars in space. And both objects are essentially vaporized. But we still have the Earth in the moon. You're like, how do I dot dot dot that to current reality? You know, you're exactly. You're exactly. right. It got vaporized, but then it coalesced, right? Gravity is very, very patient. And so even though all of its original work in the first 100 million years was ruined by this collision, it got back to work and it pulled those blobs together and it made two new blobs, one that formed the earth and then a big ring around the earth, like a ring of debris that was spinning

sort of too fast around the earth to fall into the central clump. It formed this like huge spray of material. All right. And that's why the moon's made out of the same stuff the Earth is made out of. Exactly. When we visited the Earth first and we sampled it, people were surprised to discover that it's basically the same mixture of stuff as the Earth. It's not like a different solar system body that was formed in another place and so has a different mixture of like icees and rocks and different isotopes and stuff. It's basically made out of the same stuff as the Earth. And that's because it comes from the same mixture of those two planets. Like it was the same vaporized blob of stuff.

some of it fell in towards the earth, and the stuff that was spinning around sort of too fast ended up in this big debris ring. But then gravity pulled that together into a moon. Did we have this hypothesis before we went to the moon and found what it was made of? Or did going to the moon and physically collecting samples give us this hypothesis when we were like, whoa, it's the same stuff? This hypothesis has been around for a while, but it really became the favorite once we went to the moon.

And also once we understood something about the moon's inner core, the moon's, the moon has sort of a small iron core smaller than you would expect and the hypothesis is that a lot of that iron was probably lost from when the impactor hit the proto earth and some of that was like melted and vaporized and so it would have a bigger iron core otherwise this became a much more popular hypothesis after we went to the moon and visited it and understood what it was made out of and there's a lot of really interesting physics there that's relevant to it like why doesn't it all just collapse into a planet right why doesn't it all just become one huge giant planet how come part of it ended up as a ring and that's just because you know the whole thing is spinning a lot of it

has angular momentum and so some stuff was just moving too fast to fall in the way like the moon now is moving too fast to fall into the earth it's all about that velocity and then when that stuff gathered together into a moon that stuff was spinning so the moon had some original spin right that came from the spinning motion of all of that stuff after the vaporization and we think that spin rate originally was much, much higher than it is today. So the moon used to be spinning faster than it is now. Was there, and this is maybe an unfair question, was there anything alive on Earth when it was spinning fast enough that sometimes you'd see what is now the far side of the moon? So like dinosaurs probably never saw the far side of the moon, but did like the first bacteria see the far side of the

moon? I mean, I'm sure they don't see anything that far away, but you know, could they have? Yeah, it's possible we don't really know exactly how old life is on earth but it stretches back billions of years right and so it's possible that there are critters that have lived on earth that have seen other parts of the moon that's a very cool thought because the earth has been gradually slowing down the moon's spin little by little every year and the opposite is also true but you know until 1959, no human had ever seen the backside of the moon. It was this like dark spot in our vision that we just couldn't see no matter how many thousands of years we've been staring up at the moon. Nobody had ever laid eyes on the backside until 1959, which feels really recent.

Right. And the Soviets did it, right? Yeah, they certainly did. Yeah, they beat us there with the Luna program. Their third one made it there. I think the first two maybe blew up. I was the thing that happened a lot for the Soviets? But anyway, so sorry. No, there's a really fun set of stories there. Maybe you know about it because of your book research that the Soviets were there first. And so they got to name a lot of stuff on the far side of the moon first. So they have all these Russian names.

And that, like, really annoyed the Americans at the time. And then, you know, later this international astronomical union took over the naming. So it wasn't all just, you know, named after kinds of vodka or whatever. Oh, come now. That's an unfair statement. Did the IAU change any of the names that the Soviet program had put in place or they just like stopped the Soviets from doing any more naming? I think they just stopped them.

And there's a lot of respect, I think, for the people who discover something to name it. But then I think that the Soviets were so far ahead that they didn't want them to just like name the whole thing after their favorite Soviet flower or whatever. Thank. Yes. There we go. That's good. That's good. I think there is like a Gagarin and Cs or something like that. All right, so we're going to take a quick break, and then we'll talk about what they found on the far side of the moon. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys.

Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in

plain sight that's harder to predict and even harder to stop listen to the new season of law and order criminal justice system on the iHeart radio app apple podcasts or wherever you get your podcasts my boyfriend's professor is way too friendly and now i'm seriously suspicious oh wait a minute sam maybe her boyfriend's just looking for extra credit well dakota it's back to school week on the okay story time podcast so we'll find out soon this person writes my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone.

Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet.

So, do we find out if this person's boyfriend really cheated with his professor? or not. To hear the explosive finale, listen to the OK Storytime podcast on the Iheart radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the psychology podcast. Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills and I get eye rolling from teachers or I get students who would be like, it's easier to punch someone in the face. When you think about emotion regulation, like you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome as a result of it

if it's going to be beneficial to you because it's easy to say like like go you go blank yourself right it's easy it's easy to just drink the extra beer it's easy to ignore to suppress seeing a colleague who's bothering you and just like walk the other way avoidance is easier ignoring is easier denial is easier drinking is easier yelling screaming is easy complex problem solving meditating, you know, takes effort. Listen to the psychology podcast on the IHeartRadio app, Apple Podcasts, or wherever you get your podcasts. Don't let biased algorithms or degree screens or exclusive professional networks or stereotypes. Don't let anything keep you from discovering the half of the workforce who are stars.

Workers skilled through alternative routes rather than a bachelor's degree. It's time to tear the paper ceiling and see the stars beyond it. Find out how you can make stars part of your talent strategy at tear the paperceiling.org. Brought to you by opportunity at work and the ad council. The first time we got to see the far side of the moon was 1959. Not too long after that, the Apollo astronauts were flying around the moon and got to see the far side. What kinds of things are over on the far side to see, Daniel? Well, you know, in research, it's always exciting to see something nobody's ever seen before

because you don't know what's going to be there, right? Maybe it's like a crashed alien battleship or some weird new geological formation, right? Your imagination goes crazy when you're first landing on a spot and seeing something no human has ever seen before. But, you know, in research, discovery is never guaranteed. Just because you land on new shores doesn't mean you find something fascinating. And in this case, basically, we found that the far side of the moon has more rocks and more dust. And it's not even very different from the front side of the moon. I mean, there are more craters.

There are fewer of these like seas, these lunar lava flows. But all in all, it's not that exciting. Yeah, that's the moon. Good old dependable moon. And the first time anybody actually landed there was 2019, like just a few years ago. The Chinese put a lander down and started to do a bunch of experiments. So it's only recently we started to explore it in detail. So, you know, there's still hope to find that crashed alien battleship.

Or that aliens might be living in a lavitude. We could find something even more exciting than what you've imagined. Yeah, maybe so. Or maybe we could build something that future aliens could land and discover for themselves. Like people are proposing building radio telescopes on the far side of the moon, looking out into space. Because then you'd have the whole moon to shield you from the noise of the Earth. From my perspective, that's an interesting prospect geopolitically, because if you built one of those radio telescopes, it wouldn't work as well if people put other stuff on that side of the moon. So now there's like competition for that space and can you tell someone they can't use the far side of the moon because your radio telescope is there?

Anyway, these things are complicated. But yes, it would be a good place for a radio telescope. Sounds like the kind of things, a bunch of lawyers in a conference room are going to hash out one day. So the far side of the moon is not that exciting on its own, but it is fascinating to understand why there is. is a far side of the moon. Before we dig into that, I just want to clarify something that's a common misunderstanding, which is the difference between the far side of the moon and the dark side of the moon, also the Pink Floyd album. I don't think anyone needs clarification. We all know about that. And we've all probably seen the light show if we're around 40 years old. So some people

imagine that the far side of the moon is also the dark side of the moon that like this part of the moon never sees sunlight, which is definitely not true. The dark side of the moon is the side of the moon facing away from the sun. The far side of the moon is the side facing away from the earth. And those two often don't agree. So when we have a full moon, the sun is illuminating the entire side of the moon that we are seeing because the sun is sort of behind us in space, then the back side of the moon, the far side that we don't see is also dark. But at the opposite scenario, when the moon is totally dark, when we see a new moon, and that's because, because the far side of the moon is totally lit up by the sun, right?

Half of the moon is always lit up. It's just sometimes not the side that we're seeing. So the far side and the dark side are different. It would be like a Gary Larson Pink Floyd crossover event when they meet. I'm pretty sure if you play Dark Side of the Moon backwards, it explains that. That's how you understand the far side cartoons, right? You have to listen to the Dark Side of the Moon backwards. Yeah, there was a lot of cross talk between the arts back then.

Okay, so how is this happening? The moon was going faster, you said, and it's been slowing down. Why has it slowed down to be exactly the same rotation rate and stuff? What's going on? So it's not a coincidence, right? Physics seems to like this scenario. And it's called tidal locking because it's connected to the concept of tidal forces, which are in effect we see all the time in gravity.

And it sounds complicated, but it's really pretty simple. The only thing you really have to understand is that gravity gets weaker, as distances get longer. So if you're further away from the sun, its gravity is less powerful. As you get closer to the sun, its gravity is more powerful. That makes sense.

But now imagine you're a pretty big object. So part of you is closer to the sun than another part. Then part of you is going to feel stronger gravity than the other part. And this happens all the time. Like if you were standing on the surface of the earth, then the earth is pulling on your legs harder than it's pulling on your head.

Right? And so that's a tidal force. Because there's a difference there, you can actually think about the earth as sort of like trying to pull your head off of your body. Is this like mini spaghettification? Yes, exactly. When it's very powerful, when it's more powerful than the force is holding an object together, that's spaghettification. And so when you get near a black hole, for example, gravity is super powerful. And the difference between the gravity at your feet and your head is much more dramatic and much more powerful than the force is holding your head on your body.

And so it's effectively natural decapitation or spaghettification. But lucky for us, instead of death, we get the time. Exactly. So you don't have to worry about that because the difference of the force of gravity on your feet and on your head is very, very gentle and your neck is very powerful in comparison. But the moon is pretty big. And so the difference between the gravitational force on one side of the moon and on the other is much stronger. And so what happens is that the earth basically turns the moon a little bit into a football. It like makes it a little bit oblong because it pulls on the,

closer bits more powerfully and it pulls on the further bits more gently and has the effect of sort of like stretching it out making it longer like a football instead of like a sphere this is another one of those things I'm surprised we ever figured out because when I look at the moon I would not think football it's a subtle effect right it looks like a sphere but it's slightly distorted by the gravity of the earth and that has a big impact on how it spins because now it has a gravitational preference to be aligned a certain way with the earth if it was a perfect sphere then the gravity on the object wouldn't change as it spins. But if it has a bulge, then gravity prefers that bulge to be aligned with the object. Sort of like gravity has a handle now on the moon, and it likes to pull

that bulge. So one point is towards the earth and one point is away from the earth. That's a gravitationally less energetic a configuration than having the whole thing spin. Well, all right. Okay, so I'm trying to wrap my head around this and picturing things in my head is not one of my stronger suits. But here we go. Okay, so we prefer to have a grip on the handle. Does the moon spin at a not constant speed where like we hold on to the handle for a little longer? I don't think that's what you're saying. And so what am I missing? So what happened initially is that the earth started to form these bulges on the moon and then the moon was spinning. And so these bulges were like ripples through the surface of the moon. They were like these waves that passed through

the moon. But Earth is also pulling on those bulges, right? Like if the moon has a bulge, it's like a football. And then it starts to spin away from the earth. The earth is going to pull on that nearest point a little bit and try to pull it back. And that effectively moves the bulge through the surface of the moon a little bit. And so that slows down the rotation of the moon a little bit because the earth is like tugging, trying to pull that point back towards it. And so that slows the moon down a little bit. And eventually, moon settles into a pattern where these waves, the bulge, doesn't travel over its surface anymore, like settles into one low location. And that's what the Earth prefers gravitationally. Okay. I'm with you. And so that's how gravity

makes the moon a little bit pointy and also slows down its spin. It's like stealing some of its energy a little bit to slow down its spin. But why does its spin get slowed down to exactly the right amount? Like it seems like that should just slow things down in general. It does. It slows things down in general. But at some point it starts spinning at just the right speed so that the pointy bit is always pointing towards the earth. And then the earth is happy. The gravity of the earth no longer wants to slow down the spin of the moon because the point of it is always facing the earth. And so gravity is happy because it's sort of like a ball rolling to the bottom of a valley. It's happy when it's settled in the bottom of the valley. So this is sort of like, you know, you let a marble go at the

top of a hill and it's going to roll down. It's going to oscillate past the minimum, but eventually friction and everything, it's going to settle down in the minimum. And the same thing happens. There's like friction inside the moon and the moon gets heated up a little bit by this. And the moon also speeds up in its orbit because there's like conservation of angular momentum. So you've slowed down the moon's spin a little bit and you've sped up its orbit a little bit, which is why the moon's orbital radius is increasing a little bit. And so how rare is this? Like if Earth were a little bit smaller, would this not happen? If there was like, if Mars was a little closer, would this not happen? Like, how lucky are we that it worked out this way? We're not that lucky. It's sort of the eventual

fate of almost every pair of bodies that orbit each other for long enough. And in fact, we've done it to the moon. And eventually, the moon will do it to the Earth. It's just a slower process. Whoa. Like, how slow? Like, are we going to be swallowed up by the sun before it happens? Or is my, you know, kid going to see it before they turn 80? Yes. So the Earth's rotation has already been significantly slowed by this effect from the moon. Over the 4 billion years since the Earth and the Moon were formed, the length of an Earth day has lengthened from six hours to 24 hours. So the Moon has made our days four times longer. It's slowed down the Earth's been by a big factor. And eventually, because the moon keeps tugging on the Earth and making it a little bit longer than tugging on that handle as it

passes, eventually it's going to make the Earth take 47 days to spin. And at that point, the Earth and The moon will both be tidily locked to each other. And the moon will only ever see the same face of the Earth. I don't think that's very nice of the Earth. I like having days. So I'm glad that's not going to happen in my lifetime. That would be fascinating, right? Because it would mean that half of the Earth would see the moon

and the other half would never see it. If life evolved on that planet, then like half of life wouldn't even know there was a moon. Whoa, I bet we'd have all sorts of different like creation stories. if some of us had moons and some of us didn't, that would be, that would be fascinating. Or imagine being an explorer and like settling around the world and then discovering this huge thing floating in your sky.

You're like, what? What? That would be crazy. That would be super amazing. But you're right, it's going to take a long time and well before that happens, the Earth is going to be eaten by the sun, which is going to end its life cycle in about 5 billion years,

turn into a red giant and absorb the Earth. So the moon is not. powerful enough to make that happen anytime soon. Well, on the upbeat topic of the end of our planets, let's take a break. And when we come back, you can tell us if the other moons on the other planets are doing this as well. If I live on Mars, am I going to see all of Phobos or not? holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion

actually impelled metal glass. The injured were being loaded into ambulances. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorists, Law and Order Criminal Justice System is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously supportive. Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit.

Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age.

And it's even more likely that they're cheating. He insists there's nothing between them. Do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast.

I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills, and I get eye rolling from teachers. or I get students who would be like, it's easier to punch someone in the face. When you think about emotion regulation, like, you're not going to choose an adaptive strategy which is more effortful to use

unless you think there's a good outcome as a result of it if it's going to be beneficial to you. Because it's easy to say like, go you, go blank yourself, right? It's easy. It's easy to just drink the extra beer. It's easy to ignore, to suppress, seeing a colleague who's bothering you and just like walk the other way.

Avoidance is easier. Ignoring is easier. denial is easier, drinking is easier, yelling, screaming is easy. Complex problem solving, meditating, you know, takes effort. Listen to the psychology podcast on the IHartRadio app, Apple Podcasts, or wherever you get your podcasts. And here's Heather with the weather. Well, it's beautiful out there, sunny and 75, almost a little chilly in the shade. Now, let's get a read on the inside of your car.

It is hot. You've only been parked a short time, and it's already 99 degrees in there. Let's not leave children in the back seat while running errands. It only takes a few minutes for their body temperatures to rise, and that could be fatal. Cars get hot, fast, and can be deadly. Never leave a child in a car. A message from NHTSA and the Ad Council. Okay, we're back.

So Daniel, the question that everybody wants to know, when we move to Mars, are we going to see the far side of Phobos and Demos or what? So this is a process that happens all over the solar system and all over the universe. Eventually, gravity will do its bit and distort objects from spheres into like gentle little footballs. It'll grab on those handles and it will kindly lock stuff. And so as we look around the solar system, we notice that all of the big moons, all of the 20 round moons that exist, around planets are all tidally locked to their planet. Only the round moons. And what causes a moon to be round? It's that it needs to be a certain size. Is that right?

Yeah. If you're big enough, then gravity is going to be powerful enough to pull down any big features, which is why, for example, like neutron stars have no features on them that are higher than one millimeter. And the larger the gravity, the harder it is to like keep a stack of stuff from falling down. And so if you're a pretty small object, you don't have to be very spherical because your gravity's pretty weak. If you're a big object like the moon or the earth, then you're going to end up as a sphere because stuff falls down, basically.

And stuff falls down more when you have more gravity. And so these round moons are technically not actually round, right? They're a little bit footballish, and they're all tidily locked to their planet. Most of these also orbit pretty closely, and so their gravity is pretty powerful. And the example you raised, like Phobos and Demos on Mars, these are little moons, and they're not very large.

They're not very round. And they're actually spinning really, really fast. And so while Mars is doing its job to try to tightly lock them, Phobos, for example, is not yet tidily locked. But it will be. It will be. Eventually, it's going to happen to everybody. So we've been talking about moon planets.

Has it happened to any sun and planets or planet yet? Absolutely it has. And absolutely it will, right? The sun is the most powerful source of gravity in the solar system. And so it's not going to be left out of this party. And it has mercury tidily locked in its grasp. But it's actually fascinating. It's not quite the same way as with the Earth and the Moon.

Because Mercury doesn't have as circular in orbit. It's much more elliptical. Then Mercury is tightly locked in this weird way. Instead of spinning once every time it goes around the Sun, it spins three times for every two revolutions around the Sun. And this is not something we understood for a while because we can't always see Mercury because it's so close to the Sun. There's a few spots in its orbit when it's like easy to see Mercury.

And so when people were observing Mercury, they were always seeing the same side of it. So they thought, oh, it must be in a one-to-one tidal locking. And it's only later when we got more observations than Mercury, do we notice, oh, no, it's doing this even weirder thing. That's because the orbit is not circular. And so it can, like, do another little bit of spin as it gets further away, and then it comes back around. But still, it settles into this really cool pattern, this three-two tidal locking. All right, so let's see, my very elderly mother, we're on V. I'm guessing Mercury is tidily locked.

in part because it's so close to the sun. So is Venus the next closest to being tidily locked or is it tidily locked also? Venus is next on the list to getting tidily locked. It's not yet tightly locked. In fact, Venus has a really weird orbit and spin. It takes 583 days to go around the sun, but it takes 224 Earth days to rotate. So like a Venus year only has 1.9 Venus day. Like, you only see two sunrises and two sunsets in a Venus year.

Huh. But that wouldn't bother you because Venus would have killed you in four or five different ways. Long before you cared about whether the sunrise was coming. That's right. But Venus is sort of getting there, right? Like its spin is similar to its orbital period. We actually think that's because of a collision that Venus was like smacked into by something which really changed its spin. We don't think there's been enough time for it to be like almost tightly locked by the sun.

It takes a much longer time because Venus is so far away from the sun and so small relative to the sun. All right. So we've done moon and planets. We've done comparisons between the sun and the planets. Is there any other combination of tightly locked things for us to think about? Can asteroids get tidily locked, for example? They could, but it's much harder because their gravity is so weak. Another really fascinating thing to look at are things that have.

similar masses like dwarf planets and their moons. So, for example, Pluto, no longer a planet, but it's still a dwarf planet, it's got a pretty big moon, Sharon. And these two things are mutually tidely locked already. So if you're like on Pluto and you look up, you always see the same side of the moon. And if you're on Pluto's moon and you look up, you always see the same side of Pluto. Oh, interesting. How many moons does Pluto have?

Oh, Pluto's got a bunch of moons, but most of them rotate. chaotically. They're too small to have been tidily locked so far. But it's sort of beautiful to see these things like orbiting their center of mass and facing each other. It's kind of like a dance. Yeah, that's awesome. It's beautiful. And that's not the only example of a dwarf planet. There's another one out there, a trans-Neptunian object called Aris, which is also a dwarf planet. And it's got a pretty big moon called Dysnomia, which happens to be the second largest dwarf planet moon after Pluto's moon. And these two are also tidily locked with each other. That sounds like it's a pretty common thing for dwarf planets to have moons that no, because how many dwarf planets are there?

There's a lot of dwarf planets out there. That's one reason why Pluto isn't really a planet anymore because we discovered, it's kind of a lot of them out there. And if we call Pluto a planet, we've got to call them all planets. And then we're going to have a lot of planets. And so, you know, astronomers have big arguments about where to draw the line. But there's a lot of dwarf planets out there. Right. And like, how are we going to have a mnemonic if there's 20 or something like wait no way no way all right so that's our solar system this sounds like a fundamental physics thing so i'm guessing that when we look at other solar systems they've got the same thing going on yes exactly we expect that the same thing will happen to planets around other stars and to moons around

those planets and because of sort of the way that we can discover those exoplanets we expect a lot of the ones we've seen so far have been tidely locked like the way that we discover these planets is by seeing their impact on their star. Either they pass in front of their star so they give like a little mini planetary eclipse which dims the star a little bit or they wiggle the star because of the gravity of the planet

pulling on the star. So in both cases they have to be pretty close to the star for us to see it, which means that of all the planets out there in the galaxy orbiting their stars, we're best at seeing the ones that are closest to their stars, which also means we're best at seeing

the ones that are probably tidily locked. And so astronomers have, like, done a bunch of calculations to understand the orbits of these things and the masses and predict their tidal locking. And they expect that a lot of these planets are tidily locked. Maybe one to one, maybe like three to two, the way Mercury is, or maybe like five to two. It depends a lot in the eccentricity of the orbit. What's the sort of gravitationally most preferred arrangement? Would it be fair to say that it's too far away for us to have been able outside of our solar system to see planets and their, moons being tidily locked. And so the only thing we've been able to look at so far is tidal

locking with suns and planets. Yeah, that's exactly right. Exo moons is a brand new area of study people looking for these moons around exoplanets. Super exciting. And in the next few years, as we turn on more and more space telescopes, we're going to get more and more information about these planets and their moons. And we can start to measure their spin and to understand this and to figure out like whether these planets out there, a lot of more of them are tidily locked or a lot less. You know, a question we always have is, is our solar system weird or is it typical? Like in most cases, is it just the first couple of planets closest to the sun that are tidily locked, which would align with our understanding and tell us that our solar system's not that weird?

Or maybe we'll be surprised and we'll discover, oh my gosh, all those solar systems out there, they're all tightly locked. What's going on? Something is different from what we expect. You never know when you go out into the universe and ask these questions and look for the first time. if you're just going to see like more dust and rubble or something really, really exciting. The universe is good at providing job security in the form of new questions. And it's not just stars and planets we can study. We can also look at pairs of stars. We're used to thinking about stars as like individual and you have a solar system with one star

at its core and a bunch of planets. But actually there's lots of binary star systems out there. And the reason is that stars when they're formed, it's a big cloud of gas and dust which collapses. And typically you get multiple stars from a big cloud of gas and dust. You have like little gravitational seeds that start this runaway gravitational effect. And you don't just have one seed. You have a bunch of them. So you get like a stellar nursery makes lots and lots of stars.

So we have a whole podcast episode about binary star systems and even like trinary star systems. But the point is that lots of stars out there have brothers and sisters they were born with like twins. And so they're pretty close to another star, which means that you can have. pairs of stars that are tidily locked to each other. That's awesome. Or if you have a really big planet, you could have a planet and a star that are tightly locked to each other. So the planet is always seeing the same side of the star, right?

That could be weird. Yeah, but we haven't seen that yet, right? We have not seen that yet. There's a star out there, Tao Boutis, which we suspect is tidily locked to its planet, but we're not 100% sure of that. But, you know, this kind of stuff makes a difference because it really changes the experience of being on a planet. Like if Earth was tidely locked to the sun, we'd have half of the Earth gets sunshine all day, and half of the Earth would be the dark side of the Earth. The far side

of the Earth would be the dark side, you know, where Pink Floyd plays concerts and Gary Larson draws his cartoons. And that would be the very, very cold side of the Earth, right? Dead side. Yeah, the dead side, exactly. And then you'd have this ring around the middle of the Earth that was like right on the edge, you'd be like permanent sunrise. And that might be the only place on the planet you could live because one side would be too hot and one side would be too cold and then you'd have this like Goldilocks ring around the planet that might be hospitable. Location, location, location. Exactly. And so if that's the case on some of these exoplanets, that means it'd be a lot harder

for life to form. Either they'd have to evolve to survive very hot conditions or very cold conditions or there would only be a thin strip of their planet that they could live on. And you know, then there wouldn't be seasons in the same way. It would make for, very different kind of biology. It would make it easy to study extremophiles, though, because you know exactly where you needed to go. Just, you know, the cold ones are over there and the hot ones are over there. But there probably wouldn't be a lot of funding for science in a world like that. You never know, right? And we have all these expectations for what life would be like on these planets because we imagine what our life would be like on those planets. But of course, if you

evolve on those planets, you think that's the normal way to live. And they would think it's super duper weird for like your planet to spin and get constantly bathed in sunlight or for you to have no control over whether you're seeing the sun or not because I'm tidely locked planet. It's like you don't want sun, you just move to the backside. You want sun, you move to the front side. Totally up to you. Here we're like at the mercy of celestial objects spin rates to determine when we see sun and when we don't. Yeah, I guess you get used to what you grew up with. It sure seems like It gets nice to have a more moderate in between. It certainly does.

But in the end, the universe prefers tidal lock and given enough time, gravity is going to do its business, make everything round, and then make it a little bit footballish, and it's going to tug on those gravitational handles until everything is tidily locked. Unless, of course, your sun explodes and eats you before it can even happen. But it's sort of the gravitational destiny of every other kind of object. And there's the ending that'll keep my kids from listening. and hopefully inspire a lot of crazy music and silly cartoons. Yay!

All right. Thanks very much, everybody, for exploring the physics of tidal locking with us. It turns out to play a big role in what it's like to live on our planet, what it's like to look up at the skies and understand the universe or wonder at its mysteries, and it will continue to play a big role in life on Earth. Hussah! Thanks for listening. Tune in next time. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.

1995, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. My boyfriend's professor is way too friendly, and now I'm seriously suspicious.

Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate. Maybe. Find out how it ends by, listening to the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your

podcast. Hi, it's Honey German, and I'm back with season two of my podcast. Grazias, come again. We got you when it comes to the latest in music and entertainment with interviews with some of your favorite Latin artists and celebrities. You didn't have to audition? No, I didn't audition. I haven't audition in like over 25 years.

Oh, wow. That's a real G-talk right there. Oh, yeah. We'll talk about all that's viral and trending, with a little bit of cheesement and a whole lot of laughs. And of course, the great bevras you've come to expect. Listen to the new season of dresses come again on the IHeart Radio app, Apple Podcast, or wherever you get your podcast. This is an IHeart podcast.