Latest / Daniel and Kelly’s Extraordinary Universe / Why is half of the moon always hidden?

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Why is half of the moon always hidden? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, Daniel, did you know we're not the first people
0:10
Speaker 1: to join physics and cartooning? What I thought we were
0:13
Speaker 1: definitely on the forefront there. No, you know one of
0:15
Speaker 1: my favorite comic scripts ever is named after something awesome
0:19
Speaker 1: in physics. Let me guess, Um, Calvin and Hobbs. No, No,
0:25
Speaker 1: that's philosophy, Um thinking thinking Garfield? Wait? Do you think
0:29
Speaker 1: I like Garfield? It's the same joke every time. That's true? Um?
0:34
Speaker 1: Are you thinking just because of quantum fields? Like? Maybe
0:36
Speaker 1: Garfield is another quantum field? Maybe peanuts. I don't know.
0:40
Speaker 1: I have no idea how peanuts could relate to physics.
0:42
Speaker 1: I am officially disappointed in you. All right, I give up.
1:02
Speaker 1: Hi am Jorge. I'm a cartoonists and the creator of
1:04
Speaker 1: PhD comics. Hi. I'm Daniel. I'm a particle physicist, and
1:08
Speaker 1: I have no idea what cartoons relate to physics, especially ours, right, especially,
1:14
Speaker 1: and Welcome to our podcast, Daniel and Jorge Explain the Universe,
1:17
Speaker 1: a production of I Heart Radio in which we talk
1:20
Speaker 1: about crazy things about the universe, things that are close by,
1:23
Speaker 1: things that are far away, things on one side, things
1:25
Speaker 1: on the other side, and we break it down an
1:27
Speaker 1: attempt to explain something to you that's both mind blowing
1:31
Speaker 1: and actually understandable. That's right, all the things that are
1:34
Speaker 1: both maybe right here and kind of far away, that's
1:38
Speaker 1: at the same time, that's right nearby and yet hidden.
1:41
Speaker 1: We seek to reveal those truths to you. So to
1:43
Speaker 1: be on the podcast, we will be talking about something
1:46
Speaker 1: that is basically in our everyday lives, right every well,
1:50
Speaker 1: every night live, every nightlife. Yeah, my nightlife is not
1:53
Speaker 1: that exciting anymore, but back when I used to go
1:56
Speaker 1: at at night. Yeah, it's something that I was wanking
1:59
Speaker 1: for Netflix back before kids. But yeah, this is the
2:02
Speaker 1: kind of thing you know, you can look up in
2:04
Speaker 1: the sky and easily wonder about. Yeah, it's right there
2:07
Speaker 1: almost every night, and yet we can't see it. Nobody,
2:11
Speaker 1: nobody really knows what it looks like. Right until recently,
2:13
Speaker 1: that's right, nobody had ever seen it, even though it
2:15
Speaker 1: hangs right there. And so today we're talking about what's
2:24
Speaker 1: on the far side of the moon. That's right. If
2:26
Speaker 1: you look up in the night sky often you may
2:28
Speaker 1: notice the moon, of course, and a sharp observer may
2:31
Speaker 1: notice that the moon looks similar every time. The portion
2:35
Speaker 1: of it you can see changes right, becomes a crescent,
2:37
Speaker 1: becomes larger. But if you pay attention, you notice that
2:40
Speaker 1: the features you see on the Moon are actually the
2:42
Speaker 1: same every night. Yeah, it never changes, the right. That's
2:46
Speaker 1: mind blowing to think, because the Moon is a giant
2:49
Speaker 1: sphere and we're spear and we're you know, going around
2:53
Speaker 1: the Sun spinning and the Moon is spinning around us,
2:56
Speaker 1: and yet we always see the same side of the
2:58
Speaker 1: Moon all every night. That's right, it doesn't change. One
3:02
Speaker 1: side of the Moon is the near side, that's the
3:03
Speaker 1: side the face of the Earth, and the other side
3:05
Speaker 1: faces away from the Earth towards the rest of the universe.
3:09
Speaker 1: And until nineteen fifty nine, no human had even seen
3:13
Speaker 1: a picture of it. We had no idea what could
3:15
Speaker 1: be on it. It could have been like filled with
3:17
Speaker 1: crazy lunar civilization, or you know, have a message written
3:21
Speaker 1: on it, or something like I can't believe you took
3:23
Speaker 1: you guys this long, or something. Right, it could have
3:25
Speaker 1: been filled with Israeli tardigrade. I think you're fast forwarding
3:30
Speaker 1: a few decades. Yeah, but yeah, I mean, there could
3:34
Speaker 1: have been even nothing, right. It could have been just
3:36
Speaker 1: a half sphere for all we know. We could have
3:38
Speaker 1: just been like a like a slice orange and we
3:41
Speaker 1: only see one side of it, right, Yeah, it could
3:43
Speaker 1: have been that the moon is actually a big prop
3:44
Speaker 1: right and always and if we come around the other
3:46
Speaker 1: side we see like the scaffolding and all that stuff. Um,
3:49
Speaker 1: that could have been amazing. And you know, we make
3:51
Speaker 1: a joke even known that the moon was the sphere
3:55
Speaker 1: and not just like a giant disc floating in space. Um.
3:59
Speaker 1: I think could be pretty hard to get a giant
4:01
Speaker 1: disc um in any model of moon formation. But but
4:05
Speaker 1: you never know, right, And this is why we explore,
4:07
Speaker 1: because you've got to see stuff to breally understand. You
4:10
Speaker 1: can speculate, you can say we think we know what
4:12
Speaker 1: the backside of the moon is like. Turns out when
4:14
Speaker 1: we saw it there were some surprises and until you
4:17
Speaker 1: really yeah, there were some surprises. The backside of the
4:19
Speaker 1: moon is not the same as the front side of
4:21
Speaker 1: the moon, and you know, you got to go and look.
4:24
Speaker 1: This is why we do experiments, This is why we
4:26
Speaker 1: explore the universe because until you see it, you never
4:29
Speaker 1: really know. And so only a handful of humans have
4:32
Speaker 1: actually seen the other side of the moon, right, seen it? Yeah,
4:35
Speaker 1: I mean we've had pictures, and only a handful of
4:37
Speaker 1: humans have seen it, sort of like with their own eyes. Yes,
4:40
Speaker 1: that's true. It takes you have to orbit the moon
4:43
Speaker 1: in order to see that. So yeah, only a few
4:45
Speaker 1: people have ever seen this, but you know, fewer people
4:48
Speaker 1: have ever seen my moon, not quite as prestigious. But um, yeah,
4:53
Speaker 1: let's not get into that on this podcast. Let's say
4:56
Speaker 1: that for Daniel and Jorge after dark. Okay, all right,
5:01
Speaker 1: that's folks. That's the sound of Jorge carefully stepping away
5:04
Speaker 1: backwards from that joke. No, but it's a fascinating topic,
5:08
Speaker 1: and I was wondering did people understand that because it's
5:11
Speaker 1: kind of odd. Is it like a giant cosmic coincidence
5:14
Speaker 1: or is it totally normal for us to only see
5:16
Speaker 1: one side of it? That's a that's why I'm blowing
5:19
Speaker 1: to me. Yeah, So, um, I walked around and I
5:21
Speaker 1: asked people, you know, what do they think about this?
5:24
Speaker 1: Were they aware of it, did they realized did they
5:27
Speaker 1: understand it? Could they give a physical explanation? Yeah? So,
5:29
Speaker 1: as usual, Daniel went out there somewhere in the world.
5:32
Speaker 1: Where were you at this time? Daniel? Were you in
5:35
Speaker 1: California or No? I was back in California. So these
5:38
Speaker 1: are you see Irvine summer students who answered these questions.
5:41
Speaker 1: As usual, Daniel went out and asked random people on
5:44
Speaker 1: the screen the question of the episode, and today's question was.
5:49
Speaker 1: Today's question was did you know that that half of
5:52
Speaker 1: the moon always faces away? So think about it for
5:54
Speaker 1: a second, if you had realized this, or if you
5:57
Speaker 1: knew this. I'm sure a lot of our reader listeners
6:00
Speaker 1: I knew this, but maybe you hadn't thought about it
6:02
Speaker 1: for a while. And so think about what you would
6:04
Speaker 1: answer if a random physicist approach you on the street. Yes,
6:08
Speaker 1: do you know why that is? Um? Just I know
6:11
Speaker 1: because I know that the Earth rotates and I know
6:15
Speaker 1: the Moon doesn't. And there's a reason why you don't.
6:18
Speaker 1: We only see one face in the moon and never
6:20
Speaker 1: the other. I did not know that there is a
6:22
Speaker 1: side of the Moon that did not face the Earth
6:25
Speaker 1: because the first rotation as well. Yeah, I mean my
6:27
Speaker 1: understanding is the Moon is rotating around the Earth and
6:30
Speaker 1: the Earth rotates on its axis because it's spinning. Um.
6:34
Speaker 1: But yeah, I didn't realize the Moon was spinning too.
6:36
Speaker 1: I didn't think it was. I guess because both the
6:38
Speaker 1: Moon and the Earth are rotating, and so we never
6:42
Speaker 1: see the backside related to rotations of the stellar bodies. Yes,
6:51
Speaker 1: well do you know why that? Is that a coincidence?
6:52
Speaker 1: Is there a physical reason? Physics? Physics? All right, So
6:58
Speaker 1: a lot of people didn't know, and a lot of
7:00
Speaker 1: people didn't yees. Some people were really shocked, and as
7:03
Speaker 1: soon as they understood that it was happening, they were like,
7:05
Speaker 1: that's really weird. How could that be? What? Yeah, it's
7:11
Speaker 1: almost like it's doing it on purpose, right, Like the
7:13
Speaker 1: Moon is suspicious of us and doesn't want to turn
7:15
Speaker 1: its back to us, you know, like it's it's hurling
7:18
Speaker 1: through space, but it's like I don't want to I
7:20
Speaker 1: need to be facing Earth at all time. And it's
7:23
Speaker 1: slowly backing away also, right, don't forget, we're losing it
7:25
Speaker 1: very gradually. So the moon is sort of like edging
7:28
Speaker 1: away from us the way you're edging away from my
7:30
Speaker 1: inappropriate jokes. Yeah, so I guess it's not as well
7:34
Speaker 1: known as I would have guessed it was. You know,
7:37
Speaker 1: a lot of people seem surprised, and of the people
7:39
Speaker 1: who did know that it happened, none of them could
7:42
Speaker 1: give me an explanation for why, Right, nobody understood the
7:45
Speaker 1: physics of it. People appreciated the concept, but nobody could
7:48
Speaker 1: explain why. Well, you know, I think the question I
7:50
Speaker 1: have is, um, what's the official name for it? I
7:53
Speaker 1: think we've called it the far side of the moon,
7:56
Speaker 1: the backside of the moon. Think Floyd called it the
7:59
Speaker 1: dark side of the moon. It's called the far side
8:01
Speaker 1: of the moon, right, And I think that's probably the
8:04
Speaker 1: inspiration for that cartoon, right, the far side, because like,
8:07
Speaker 1: what's going on over there, like the weird hidden side. Um,
8:11
Speaker 1: though I'd love to ask Gary Larson about that one day.
8:14
Speaker 1: It's not the dark side of it because oh, actually
8:18
Speaker 1: I do know the answer to that, because I just
8:20
Speaker 1: read a little bit of his biography. What is the answer?
8:23
Speaker 1: The answer is he had another name for it, but
8:25
Speaker 1: then when he sold it to a syndicate or a newspaper,
8:27
Speaker 1: they said, hey, how are we call it the far side?
8:29
Speaker 1: And He's like, sure, editors actually contribute something, I've never
8:34
Speaker 1: heard of that before. That's that's the anti climatic story.
8:39
Speaker 1: And if our editors listening to this podcast, we love
8:42
Speaker 1: everything you suggested, by the way, that's right, and we
8:44
Speaker 1: meant newspaper that's right. Comic editors. No, So the far
8:48
Speaker 1: side is the back side of the moon, the side
8:50
Speaker 1: of the Moon that always faces away into the cosmos,
8:52
Speaker 1: away from the Earth. The dark side of the Moon
8:55
Speaker 1: is the name of a pink fluid album, right, And
8:58
Speaker 1: it's not the same thing because is the side of
9:01
Speaker 1: the Moon that's lit up is the side of the
9:02
Speaker 1: Moon that faces the Sun, right, not the side of
9:05
Speaker 1: them in the faces the Earth. So the dark side
9:07
Speaker 1: of the moon is the side of the Moon that
9:09
Speaker 1: faces away from the Sun. Right. So sometimes the far
9:12
Speaker 1: side of the moon is lit up, like when the
9:15
Speaker 1: moon is right between the Earth and the Sun, then
9:17
Speaker 1: the far side is totally bright and the near side
9:20
Speaker 1: is totally dark. Oh wow, I never thought about that before. Yeah,
9:25
Speaker 1: because I guess the far side of the moon gets
9:27
Speaker 1: lit up sometimes it does. And so like sometimes the
9:30
Speaker 1: sun is just like blasting with energy, but there's nobody
9:33
Speaker 1: there to look, right. It's like whatever secrets the far
9:36
Speaker 1: side of the moon holds, you know, are being revealed
9:39
Speaker 1: by the sun, but nobody's looking at it. So, right,
9:42
Speaker 1: all those beautiful lunar sunsets and sunrises, nobody there to
9:46
Speaker 1: appreciate it. Because the moon doesn't have a stable dark side, right,
9:49
Speaker 1: it's not always the same side that's dark. The temperatures
9:52
Speaker 1: on the moon very like crazy, right. If you're on
9:55
Speaker 1: the bright side of the moon, it can get warmer.
9:58
Speaker 1: If you're on the dark side of the moon, it
9:59
Speaker 1: gets like super duper cold. And because the no atmosphere
10:03
Speaker 1: to hold in the temperature, it basically as the boundary
10:06
Speaker 1: between the bright side and the dark side moves across
10:09
Speaker 1: the surface of the of the moon, the temperature just
10:12
Speaker 1: like plummeting super quickly. So the dark side of the
10:14
Speaker 1: moon changes all the time, but the far side of
10:17
Speaker 1: the moon never changes. That's the weird part. It's right,
10:21
Speaker 1: and you heard, and it's never changed, or it's it's
10:25
Speaker 1: you know what I mean, Like, are we looking at
10:26
Speaker 1: a different moon than humans ten thousand years ago, or
10:29
Speaker 1: it's never changed. That's a great question. You know, in
10:33
Speaker 1: old drawings of the moon it looks the same, but
10:35
Speaker 1: that only goes back you know, like a thousand years
10:38
Speaker 1: or so. But the physics that will explain it in in
10:40
Speaker 1: a few minutes suggests that it hasn't changed in a
10:42
Speaker 1: long long time. It shouldn't be stable, and that is
10:46
Speaker 1: so weird. It is weird and you know, let's describe
10:48
Speaker 1: exactly how weird that is, because in people's responses you
10:51
Speaker 1: could hear there was some confusion about like exactly what's
10:54
Speaker 1: doing the spinning and what could be affecting it. So
10:57
Speaker 1: let's go through that in some detail and explain what's
10:59
Speaker 1: happened before we explain why. Because the Earth is spinning around,
11:03
Speaker 1: brispinning around, and the Moon is spinning around us at
11:06
Speaker 1: a different rate, right, And the only things you really
11:09
Speaker 1: need to think about. You don't need to think about
11:11
Speaker 1: the fact of the Earth spins, that doesn't matter, or
11:13
Speaker 1: the Earth is orbiting the Sun. The only two things
11:15
Speaker 1: you need to think about are the Moon moving around
11:18
Speaker 1: the Earth. Right. The Moon is in orbit around the Earth.
11:21
Speaker 1: It goes around the Earth, and the Moon is spinning.
11:24
Speaker 1: It's kind of like we are spinning around the Sun
11:27
Speaker 1: once every year, but we're also spinning in place kind
11:29
Speaker 1: of that's right, once exactly, and a different part of
11:31
Speaker 1: the Earth faces the Sun literally every day. Right. It's
11:35
Speaker 1: the Earth doesn't have a near side and the far
11:37
Speaker 1: side to the Sun. Right. So, and that's because we orbit,
11:42
Speaker 1: it takes us a whole year to go around, right,
11:44
Speaker 1: it only takes us a day to spin right, but
11:48
Speaker 1: in the case of the Moon, it spins it exactly
11:51
Speaker 1: the right speed, so that the same side of the
11:54
Speaker 1: of the moon is always facing the Earth. Those two numbers,
11:57
Speaker 1: how long it takes to go around the Earth and
12:00
Speaker 1: how fast it spins around are perfectly sincd up, so
12:05
Speaker 1: that the same side of the Moon is always facing
12:07
Speaker 1: the Earth. Oh and not just sinked up, but they
12:10
Speaker 1: had to be syncd up going the opposite way, right. Yeah,
12:14
Speaker 1: if the Moon is going around the Earth clockwise, then
12:17
Speaker 1: the moon has to be going around spinning in place
12:20
Speaker 1: counterclockwise at exactly the same number of times per per
12:25
Speaker 1: day or per night. Um, let me just check that
12:28
Speaker 1: my mental model here, it's hard to figure out. So
12:30
Speaker 1: if it's moving around clockwise, imagine the nearest you have,
12:33
Speaker 1: the near side, started twelve o'clock right, and the near
12:36
Speaker 1: side of the moon is of course facing the Earth.
12:38
Speaker 1: If the moon didn't rotate, then by the time you've
12:40
Speaker 1: got to six o'clock, then the what we call the
12:43
Speaker 1: far side of the moon would be facing their Earth.
12:46
Speaker 1: So in order for that not to happen, it also
12:48
Speaker 1: has to rotate actually clockwise right, So it moves around
12:51
Speaker 1: the Earth clockwise and it rotates clockwise so that it's
12:55
Speaker 1: the same side as always facing the Earth. Right. Yeah,
12:58
Speaker 1: it's tricky. Yeah, yes, sorry, I got that totally. It's
13:02
Speaker 1: hard to hard to keep chaco. Hey, editor, can you please,
13:07
Speaker 1: can you make Jorge never say anything wrong? Yeah? Can
13:09
Speaker 1: you make me sound a little bit more intelligent? There?
13:12
Speaker 1: Thank you? Yeah, there you go. Um, oh, you're right,
13:14
Speaker 1: you're right. It has to um kind of like spin.
13:17
Speaker 1: Oh wow. Yes, it has to spend the same direction
13:21
Speaker 1: at the same rate, exactly, has to spend the same
13:22
Speaker 1: direction at exactly the same rate. And you know, anytime
13:25
Speaker 1: you see a coincidence in physics, like these two numbers,
13:28
Speaker 1: which could be different, happen to be exactly the same thing,
13:32
Speaker 1: you got to look for a physical reason because either
13:34
Speaker 1: it's a ginormous coincidence, or it's a signal from the
13:38
Speaker 1: folks who invented the simulation that is our universe, or
13:40
Speaker 1: there's a physical reason that it has to be that way, right, right,
13:44
Speaker 1: because it's it's it's I feel like it's rare, right,
13:47
Speaker 1: Like the Earth doesn't do that around the Sun, and
13:50
Speaker 1: none of the other planets do that around the sun, right,
13:53
Speaker 1: Like they not just spin at different speeds, but they
13:56
Speaker 1: spin in like different axes and different directions, and so
14:00
Speaker 1: it's it's like, just because you're going around in a
14:03
Speaker 1: larger object, doesn't mean that you're going to have this
14:05
Speaker 1: perfectly sincd orbit. Right. Um, yeah, you're right. None of
14:08
Speaker 1: the planets in our Solar system have this same feature,
14:11
Speaker 1: though there are some other moons. Some of the moons
14:13
Speaker 1: of Jupiter do the same thing to Jupiter, right, So,
14:17
Speaker 1: and that's a clue, right, because if you have a
14:19
Speaker 1: one coincidence, that's crazy. If you have the same coincidence
14:22
Speaker 1: several times, then you know that's a sign that there's
14:25
Speaker 1: some physics happening. I think you're telling me that it's
14:27
Speaker 1: all due to this very interesting physical effect, right, Like
14:31
Speaker 1: there's a physics of why this happens. There's definitely some physics. Yeah, yeah,
14:35
Speaker 1: so let's get into it. But first let's take a
14:37
Speaker 1: quick break. All right. We're talking about why the moon
14:53
Speaker 1: always looks the same every night all the time, Like
14:58
Speaker 1: it's it's out there spinning around on the Earth, and
15:00
Speaker 1: it's spinning around it's its own axis, but it always
15:03
Speaker 1: seems to face the Earth the same way, and so
15:07
Speaker 1: that's weird. Right. Yeah, it's due to an effect called
15:11
Speaker 1: tidal locking, which is connected to something we've talked about
15:14
Speaker 1: several other times called tidal forces. And it's pretty simple, right,
15:18
Speaker 1: like the like the tides of the ocean, Just like
15:20
Speaker 1: the tides of the ocean. Right, it's the same effect, um.
15:23
Speaker 1: And the idea is the gravity will pull more strongly
15:26
Speaker 1: on stuff that's nearby than stuff that's far away. Right.
15:29
Speaker 1: That makes perfect sense. We're familiar with that, but we're
15:32
Speaker 1: used to thinking about objects sort of as points. Like
15:35
Speaker 1: the Earth goes around the Sun, we just think about
15:37
Speaker 1: the whole the force on the whole Earth, right, Or
15:39
Speaker 1: the Moon goes around the Earth, we think about the
15:41
Speaker 1: force on the whole moon. But the moon is kind
15:43
Speaker 1: of big, right, which means that the force on the
15:45
Speaker 1: close side of the Moon is stronger than the force
15:48
Speaker 1: on the far side of the moon. Right, the Earth
15:51
Speaker 1: is pulling the parts of the Moon that are closest
15:55
Speaker 1: to it more than it's pulling the stuff that's in
15:57
Speaker 1: the behind it, exactly. And those are called tide forces.
16:01
Speaker 1: And if tidal forces are strong enough, like if you're
16:03
Speaker 1: near a black hole, then the difference in the force
16:06
Speaker 1: on one side of the object and the other can
16:08
Speaker 1: be enough to tear it apart. Right, And you might
16:11
Speaker 1: be thinking tear it apart. What if you're pulling on
16:13
Speaker 1: something with two different forces in the back on the
16:15
Speaker 1: front side, that's the same thing as pulling it apart.
16:18
Speaker 1: That's the same thing as applying a force from one
16:20
Speaker 1: side to the other. And so for example, if you
16:23
Speaker 1: get too close to a black hole, you will literally
16:25
Speaker 1: get shredded into bits. And you know, we've seen this before,
16:28
Speaker 1: like Shoemaker Levy was a comet that came too close
16:31
Speaker 1: to Jupiter and Jupiter pulled it apart into twenty six pieces.
16:35
Speaker 1: It still went around the Sun and slammed into Jupiter,
16:37
Speaker 1: so it got its revenge. But tidal forces are a thing.
16:41
Speaker 1: Anytime you have an object that's large compared to the
16:43
Speaker 1: force of gravity, then it's gonna have a big difference
16:46
Speaker 1: in the gravity on one side and the other. And
16:48
Speaker 1: that's the same way the Moon makes tides on Earth, right,
16:51
Speaker 1: it pulls the water closer to it to make the tides.
16:55
Speaker 1: But it's not just what big objects in space, it's
16:57
Speaker 1: it's it's like happening all the time to every one everywhere, right,
17:01
Speaker 1: that's right, Yeah, Like if I stand up, If I
17:03
Speaker 1: stand up right here in my studio, my feet are
17:07
Speaker 1: getting pulled by the Earth more than the top of
17:10
Speaker 1: my head. That's right, the Earth is literally pulling you apart. Now,
17:13
Speaker 1: your body is strong enough to withstand that fairly small
17:17
Speaker 1: difference between the force and your head and the force
17:19
Speaker 1: and your feet. But yes, the Earth is trying to
17:21
Speaker 1: pull you apart, unless you're lying down flat, in which
17:23
Speaker 1: case the Earth is pulling out every part of you
17:25
Speaker 1: the same way. And if you're really tall, you know,
17:29
Speaker 1: then um, then the Earth might pull you, pull you
17:31
Speaker 1: to bits. But it mostly happens to large objects where
17:34
Speaker 1: the distance between one side and the other side is large,
17:37
Speaker 1: so that the magnitude of the force of gravity is
17:41
Speaker 1: large between the between the two and that's when you
17:44
Speaker 1: difference is larger exactly, So the difference is larger and
17:48
Speaker 1: the and the Moon is big enough that the Earth's
17:50
Speaker 1: gravity pulls one part of it harder than the back
17:54
Speaker 1: side of it, and it actually changes the shape of
17:57
Speaker 1: the Moon a little bit. So the moon is not
17:59
Speaker 1: a sphere. It's like and it's like an obloid object,
18:02
Speaker 1: like a three D ellipse. The moon is not perfectly spherical,
18:05
Speaker 1: it's not perfectly spherical because it's getting squeezed by the Earth.
18:09
Speaker 1: And if these tidal forces were stronger, then the Earth
18:11
Speaker 1: and the Moon get pulled apart. Right, That's what happens
18:14
Speaker 1: when a moon gets too close to a planet, for example,
18:17
Speaker 1: it can get pulled into pieces and that's and turned
18:20
Speaker 1: into rings. Right. And so the Moon is in this
18:23
Speaker 1: place where it's close enough to the Earth to be
18:25
Speaker 1: an orbit, close enough to have these strong tidal forces,
18:28
Speaker 1: but not so close that the Earth pulls it apart. Interesting,
18:31
Speaker 1: and so Earth kind of squishes the Moon out of
18:34
Speaker 1: out of us perfectly spherical shape. But but then how
18:37
Speaker 1: does that relate to why we only see one side
18:40
Speaker 1: of it? Well, because then it gets stuck. Right, So
18:42
Speaker 1: now the moon is not a sphere, it's an ellipse.
18:45
Speaker 1: And the half that's closer to the Earth is even
18:48
Speaker 1: closer than it was back when it was a sphere. Right,
18:50
Speaker 1: It's like it's fallen down a little bit, and so
18:53
Speaker 1: that part gets heavier, right, has a stronger force of gravity.
18:56
Speaker 1: And on the back side it's an ellipse also, and
19:00
Speaker 1: part it gets even lighter. So now the near side
19:03
Speaker 1: of the Moon weighs more than the back side of
19:05
Speaker 1: the moon, meaning it's a stronger force of gravity. So
19:08
Speaker 1: now it's sort of stuck. Right, It's like a ball
19:10
Speaker 1: in a hole. Um, the close side of them can't
19:13
Speaker 1: can't spin away, right, because if it spins, then the
19:17
Speaker 1: fat part gets pulled back towards the Earth. You know.
19:21
Speaker 1: Imagine you have like a bicycle wheel, right, and you're
19:23
Speaker 1: holding it, and it spins freely, and it's happy to
19:26
Speaker 1: be in any arrangement, right. It spins because every arrangement
19:29
Speaker 1: is the same if it's a perfect circle. But now
19:32
Speaker 1: put something heavy on one spot of the bicycle wheel,
19:35
Speaker 1: what's gonna happen. It's going to prefer for that part
19:37
Speaker 1: to be down right, and if you push it away
19:39
Speaker 1: a little bit, it's gonna spin back so that the
19:41
Speaker 1: heavy part is down That's what happened to the moon.
19:44
Speaker 1: The near side of the moon is heavier than the
19:47
Speaker 1: far side because it's closer to the Earth and sort
19:49
Speaker 1: of it's sort of stuck in that way, and that's
19:52
Speaker 1: the reason. That's the reason why we only see the
19:54
Speaker 1: one side of the moon. That's the reason it's called
19:56
Speaker 1: tidal locking. Right, Tidal forces change the shape of it
19:59
Speaker 1: a little bit and then that shape makes it more
20:01
Speaker 1: conducive to always face the heavier side towards the planet.
20:05
Speaker 1: And so it happened to the Moon, and it's happened
20:07
Speaker 1: to several moons of Jupiter, and it's not that uncommon thing.
20:11
Speaker 1: So it's not a coincidence at all, Right, it's a
20:13
Speaker 1: it's physics, So blame the tides. The tidal forces of
20:17
Speaker 1: the Moon caused tides on Earth, but the tidal forces
20:20
Speaker 1: of the Earth caused the Moon to always have a
20:23
Speaker 1: near side. But wait, I'm a little bit confused. In
20:26
Speaker 1: order for the Earth to deform the moon, doesn't the
20:30
Speaker 1: Moon need to be stationary, do you know what I mean? Like,
20:33
Speaker 1: if the Moon was spinning, then this tidal force would
20:36
Speaker 1: even out across all sides, right, kind of like the
20:39
Speaker 1: Earth is a little bit fat around the middle because
20:42
Speaker 1: we're spinning and part of it gets more attracted to
20:46
Speaker 1: the Sun sometimes. Yeah, if that's a good point, I
20:48
Speaker 1: think if the Moon was spinning fast enough, it might
20:50
Speaker 1: have been able to avoid this, right, because it could
20:54
Speaker 1: it could sort of spin out of that little well
20:56
Speaker 1: that it gets stuck in and have another part of
20:58
Speaker 1: it stretched, So the stretching would be even doubt um.
21:01
Speaker 1: But I guess that just means that in the early days,
21:03
Speaker 1: the Moon was not spinning fast enough to avoid this. Remember,
21:06
Speaker 1: the Moon formed out of debris, right, The Moon was
21:10
Speaker 1: just a big cluster of debris. It's not like the
21:11
Speaker 1: Moon was a perfect sphere that was spinning and then
21:14
Speaker 1: just sort of placed on Earth. It was formed in place, right,
21:18
Speaker 1: and the Earth had a role in in that formation.
21:21
Speaker 1: Oh and when it formed, it formed in this weird,
21:25
Speaker 1: deformed shape which locked it into always facing the right
21:29
Speaker 1: the same way. Yea, So it probably was never a sphere, right,
21:31
Speaker 1: It's not like back in its early days and its youth,
21:34
Speaker 1: it remembers being having a perfect body and then the
21:37
Speaker 1: Earth ruined it. And then and then it looked up
21:40
Speaker 1: with the Earth and exactly, Oh, I see the Moon
21:45
Speaker 1: formed into the right blob, into that blob. Right. And
21:48
Speaker 1: but that also means that all of the debris that
21:51
Speaker 1: formed the Moon didn't have a lot of spin to it, right,
21:55
Speaker 1: Like maybe it was sort of basically kind of static
21:59
Speaker 1: when it formed, because it would you know, you know,
22:01
Speaker 1: I mean like if it formed out of the debris
22:02
Speaker 1: that's moving, flowing, polling around, it would eventually coalesced into
22:06
Speaker 1: a spinning ball, right. Yeah, basically everything has some angular momentum, right,
22:11
Speaker 1: because it didn't have no anglar momentum, would mean for
22:14
Speaker 1: everything that magically cancel out. So if you just took
22:17
Speaker 1: all that debris, And for those of you who aren't
22:19
Speaker 1: familiar with how the Moon is formed, we did a
22:21
Speaker 1: whole podcast episode about how the Moon probably came from
22:25
Speaker 1: something the collision of a small planetoid with an early Earth,
22:28
Speaker 1: and a huge amount of debris was thrown out into
22:30
Speaker 1: space and and some of that stuff coalesced into rings
22:33
Speaker 1: and then eventually into the Moon, and so it's you
22:37
Speaker 1: know there, We don't have a lot of information about
22:39
Speaker 1: exactly what that collision looked like, but the amount of rotation,
22:43
Speaker 1: amount of spin in that debris depends a lot on
22:45
Speaker 1: like how that first planetoid hit the proto Earth, how
22:49
Speaker 1: much spin there was. There must not have been a
22:51
Speaker 1: lot of spin, because if there had been a lot
22:53
Speaker 1: of spin, then it would you know, the Moon would
22:56
Speaker 1: have started out spinning and maybe this title force would
22:58
Speaker 1: not have deformed it into the right block. Spinning past
23:01
Speaker 1: is a good defense against getting stretched out by title forces. Yeah,
23:06
Speaker 1: it's a good good way to keep your ship keeping shape.
23:08
Speaker 1: That's right. I recommend spin classes to the moon. There
23:12
Speaker 1: you go. Cool. So that title forces is the reason
23:16
Speaker 1: that we always see the same side of the moon.
23:18
Speaker 1: Physics explains it in the end, one more mystery dismantled
23:21
Speaker 1: by physics. Once more, the magic is gone, thanks to you,
23:25
Speaker 1: Moon magic for thousands of years. All right, now let's
23:28
Speaker 1: get into what is on that far side of the moon?
23:32
Speaker 1: Are there? Aliens? Are there? Nothing? Are there? Is there
23:36
Speaker 1: a secret message to you? That's right. But first let's
23:39
Speaker 1: take a quick break. All right, we're talking about the
23:54
Speaker 1: Moon and why it always looks the same every night.
23:57
Speaker 1: It doesn't seem to be spinning the Moon, even though
24:00
Speaker 1: it's a giant spherical object. And so we figured out
24:04
Speaker 1: we talked about that it's due to tidal locking. So
24:07
Speaker 1: it formed in such a way that it's always spinning
24:11
Speaker 1: at the right rate that we always see it the
24:14
Speaker 1: same way. That's right. The near side of the Moon
24:16
Speaker 1: has basically become heavier because it's turned into a little
24:19
Speaker 1: bit of an ellipse, and that makes it prefer to
24:21
Speaker 1: keep that side to the Earth. I imagine that that
24:24
Speaker 1: wasn't always the case. You know, when the first can
24:26
Speaker 1: you imagine being on the Earth. When the Moon formed, like,
24:29
Speaker 1: you know, I think that'd be pretty hot and nasty,
24:31
Speaker 1: given that it formed at a huge collision in the
24:33
Speaker 1: Earth is basically a ball of lava. Yeah, that'd be
24:37
Speaker 1: a short trip. Okay, not so romantic, no, no, no, hot, nasty,
24:43
Speaker 1: but not in a good way. Alright. So, due to
24:45
Speaker 1: this tidal force, the Moon when it formed, forms such
24:49
Speaker 1: a way that it basically got locked into always facing
24:51
Speaker 1: the Earth the same side, that's right, which means that
24:55
Speaker 1: there's a side of the Moon that we cannot see
24:57
Speaker 1: from the Earth, and people didn't see until nine when
25:02
Speaker 1: the Soviets finally sent something up there to take a
25:04
Speaker 1: picture of it. Really was the Soviets who first saw it. Yeah,
25:08
Speaker 1: I remember back in the day, the Soviets were leading
25:10
Speaker 1: us in the space race, right in the fifties and
25:12
Speaker 1: the early sixties, spot Nick and all that stuff. Um,
25:15
Speaker 1: they were ahead. And actually it's pretty funny because the
25:18
Speaker 1: Soviets were there first, right, they have the first ones
25:20
Speaker 1: to see this stuff, and so the Soviet scientists they
25:23
Speaker 1: just started naming things in Russian right and bold. This
25:26
Speaker 1: annoyed the Americans, not only because they didn't get to
25:29
Speaker 1: see it first, and they didn't get take the first pictures.
25:32
Speaker 1: But now everything on the back side of the Moon
25:33
Speaker 1: is like has some crazy Russian name. Wow is that true? Yeah?
25:37
Speaker 1: Totally You think I just make this stuff up? Maybe,
25:43
Speaker 1: uh no, this is totally true. Well, um, so they
25:46
Speaker 1: they what did they send like a satellite and it
25:48
Speaker 1: took pictures as it went around the back side of
25:50
Speaker 1: the moon exactly. Yeah. And back then, you know, we
25:53
Speaker 1: didn't have digital photographs and all this kind of stuff.
25:56
Speaker 1: So they they had like the pictures first, and they
25:58
Speaker 1: started naming the craters and the features exactly. So everything
26:02
Speaker 1: on the backside is named in Russian. It started out
26:05
Speaker 1: that way, but then the Americans got the International Astronomical
26:08
Speaker 1: Union to intervene, and then they decided to do a
26:11
Speaker 1: sort of international process, which is you know, um, what
26:15
Speaker 1: do you mean intervened, Like they were in the middle
26:17
Speaker 1: of naming things and then they're like whoa, whoa stop stop, yeah,
26:21
Speaker 1: exactly exactly. Anyway, it turns out that the back side
26:25
Speaker 1: of the Moon is not just like the near side
26:27
Speaker 1: of the moon, right, it's not exactly this different. How
26:30
Speaker 1: can it be different? Yeah, it's still sort of a mystery.
26:33
Speaker 1: We don't actually still understand it. Now, it's not dramatically different.
26:36
Speaker 1: I mean, in the end, it's still just rocks and dust, right,
26:39
Speaker 1: it's not like there's a glittering ocean there or some
26:42
Speaker 1: civilization or like crazy mountains or anything like that. No,
26:46
Speaker 1: it turns out that there are more craters. And you know,
26:48
Speaker 1: if you look at the Moon from the Earth, you
26:49
Speaker 1: see these sort of pop marks and these also see
26:52
Speaker 1: these open areas that we call seas, even though there's
26:55
Speaker 1: no water in them. And the backside of the Moon
26:57
Speaker 1: has more of these craters and fewer of the sea,
27:00
Speaker 1: so it has a different complexion. Yeah, exactly, it has
27:03
Speaker 1: more acne. And you might be tended to think, oh,
27:06
Speaker 1: that's because you know it's facing out and so it's
27:09
Speaker 1: going to get hit, right, but like a shield. Yeah,
27:12
Speaker 1: but the Earth is not actually a very large in
27:14
Speaker 1: the sky of the of the moon, right. The Moon
27:17
Speaker 1: is kind of far away, and the Earth only protects
27:20
Speaker 1: the Moon by about like three of its sky or something.
27:24
Speaker 1: So if there's a rock aiming at the Moon, it's
27:26
Speaker 1: most likely still just going to hit the Moon. Um,
27:29
Speaker 1: so that's not enough to account for the difference. And
27:31
Speaker 1: remember both sides the gravity like the Earth gravity protects
27:35
Speaker 1: the Moon's like this side of the moon. Maybe no, no, no,
27:38
Speaker 1: it's not it's not a big enough effect, and so
27:41
Speaker 1: it's a big mystery. You know. There's a lot of
27:43
Speaker 1: speculation that maybe, um, there's more like tectonic activity on
27:47
Speaker 1: the front side of the Moon, which is sort of
27:49
Speaker 1: smoothing it over. Remember we talked about Eurroba, that weird
27:52
Speaker 1: moon that has almost no craters on it that are
27:55
Speaker 1: older than like ten or twenty years old. Because there's
27:58
Speaker 1: a lot of resurfacing, like stuff coming up and making
28:00
Speaker 1: a new surface. It could be that that's happening more
28:03
Speaker 1: quickly on the front side of the moon and in
28:05
Speaker 1: the backside, but people don't really understand, like why would
28:07
Speaker 1: that be. So there's some interesting mysteries there. It's like
28:10
Speaker 1: squishy are on this side. Yeah, sometimes sort of getting refreshed, right,
28:15
Speaker 1: Like the near side of the moon gets its skin scrubbed,
28:19
Speaker 1: it gets a spa treatment more often. I think the
28:21
Speaker 1: moon is just thinking, like, you know what, nobody's going
28:23
Speaker 1: to look at my back side. Nobody cares. There's nobody
28:28
Speaker 1: back here. I'm just gonna let it go. Yeah, And folks,
28:31
Speaker 1: this is your motivation, you know, keep your hygiene spherical,
28:35
Speaker 1: keep your back end agone free. Yeah, there's hygiene advice
28:41
Speaker 1: from a scientist and a cartoonist. That's definitely who you
28:44
Speaker 1: want to be listening to. So why do you think
28:47
Speaker 1: there's more churn or more like volcanic activity on this side?
28:50
Speaker 1: Is it related to the fact that it's being it's
28:53
Speaker 1: closer to the Earth. It could be, right, I mean,
28:55
Speaker 1: we're talking about how the Moon is formed and the
28:57
Speaker 1: internals of it and what's going on inside and is
29:00
Speaker 1: it still hot enough to like flow and move around. Um,
29:04
Speaker 1: But it's it's something we've only recently really started to
29:06
Speaker 1: explore and to understand, and so it's still a question.
29:10
Speaker 1: Lunar scientists don't know the answer to this as far
29:12
Speaker 1: as I'm aware, So it's it's an open question. And
29:14
Speaker 1: you know, until recently, we didn't know basic stuff about
29:16
Speaker 1: the Moon, like does it have a strong magnetic field?
29:18
Speaker 1: And you know, why are there pockets of magnetism here
29:21
Speaker 1: and there? And so you know, even though we we
29:23
Speaker 1: went to the Moon fifty years ago, we haven't been
29:26
Speaker 1: back very much, and so there's a lot of questions
29:28
Speaker 1: we just don't have answers to. You know, I think
29:30
Speaker 1: people who study the moon are officially like to be
29:32
Speaker 1: called moonies. Well, you're in charge of naming, so if
29:36
Speaker 1: they're not called that, if they weren't called that before,
29:39
Speaker 1: they are now. All right. So that's the far side
29:41
Speaker 1: of the moon. And Daniel was it's somewhere that we
29:43
Speaker 1: want to go or is it would be interesting to
29:45
Speaker 1: go to or you know, for vacation or for science.
29:49
Speaker 1: I wouldn't recommend it for vacation, but it is interesting
29:52
Speaker 1: just because it's not well explored, which means there's always
29:55
Speaker 1: an opportunity for surprises, right, which is sort of my
29:58
Speaker 1: whole philosophy about science. It's like, science is about exploration.
30:02
Speaker 1: You can think you know what something is gonna do,
30:03
Speaker 1: you can think you know what something's gonna look like,
30:05
Speaker 1: you can think you you know whether there are particles there,
30:08
Speaker 1: But until you go and look, you haven't given yourself
30:11
Speaker 1: the opportunity to be surprised by the universe. And so
30:14
Speaker 1: it's definitely worth exploring because it's also not that far away.
30:17
Speaker 1: And it was in twenty nineteen, right this year, that
30:21
Speaker 1: humans finally landed something on the far side of the moon. Really,
30:25
Speaker 1: that's right, Yeah, just now, just a few months ago
30:28
Speaker 1: China landed something and took a bunch of pictures and
30:31
Speaker 1: is doing experiments over there, And so it's an interesting place, right,
30:35
Speaker 1: Like do we understand how the Moon formed? It gives
30:37
Speaker 1: us insights to how planets formed in the early history
30:40
Speaker 1: the Earth and stuff. It's also not a terrible place
30:43
Speaker 1: to do science because it's shielded by the whole Moon
30:47
Speaker 1: from all this noise of radio broadcast and annoying podcast
30:50
Speaker 1: hosts and all that stuff that's spewing stuff out into space.
30:55
Speaker 1: So if you want to build, for example, a radio telescope,
30:57
Speaker 1: that's a really nice quiet spot. It's the most you
31:00
Speaker 1: can get away from other people. Exactly, it's an introverts vacation, exactly.
31:06
Speaker 1: There you go. That's how you how that's how you
31:09
Speaker 1: market it. But you can only market it to like
31:11
Speaker 1: one introvert at a time, if you speak Russian and
31:14
Speaker 1: and one a quiet place too with no signal and
31:17
Speaker 1: you're on your phone. The far side of the moon
31:19
Speaker 1: would be ideal. Yeah, the market for that are super
31:23
Speaker 1: zillionaire Russian introverts, right, which I imagine there might be
31:29
Speaker 1: a few, right, must brush you have a bunch of
31:31
Speaker 1: millionaires zillionaire Russian introvers listening to this podcast, we will
31:34
Speaker 1: sell you a ticket to the far side of the moon.
31:36
Speaker 1: That's right. We will tell you how to get there, exactly, exactly.
31:40
Speaker 1: But it's one of my favorite kind of things because
31:42
Speaker 1: people can really grasp it. You can look up at
31:44
Speaker 1: the sky and you can think, you know, it's crazy
31:46
Speaker 1: that my ancestors and my ancestors ancestors, I've all been
31:49
Speaker 1: looking at the same thing hanging the sky, and the
31:52
Speaker 1: same side of it too, also not seeing the same thing.
31:55
Speaker 1: We we don't see, yeah exactly that for thousands of years,
31:59
Speaker 1: no human who had been looking up at the sky
32:00
Speaker 1: had seen the backside of this thing until basically our generation,
32:04
Speaker 1: right for the generation before us, finally cracked this mystery,
32:07
Speaker 1: finally lifted our eyeballs off the surface so we could
32:11
Speaker 1: see the other side of this thing, which is right
32:13
Speaker 1: there in our faces. Cool. Well, it's amazing to think
32:16
Speaker 1: there are still mysteries even as close as the moon, right,
32:19
Speaker 1: there are mystery places that are hard to get to,
32:22
Speaker 1: but just unexplained phenomena in physics. Yeah, yeah, exactly, And
32:26
Speaker 1: that's you know, that's why physics goes on, right, because
32:28
Speaker 1: there are always mysteries. Some people ask me, like, you know,
32:32
Speaker 1: are we ever going to figure things out? And I'm
32:33
Speaker 1: pretty sure there's always going to be some person with
32:36
Speaker 1: a question out there, you know, why is this this way?
32:38
Speaker 1: Why isn't it that way? And why does this look
32:40
Speaker 1: different from this other thing? Um, there's always questions to
32:43
Speaker 1: be answered, and they're always interesting insights to be uncovered
32:46
Speaker 1: when you dig into those questions. Each one is like
32:49
Speaker 1: a little thread in the fabric of the universe which
32:51
Speaker 1: if you tug on, it might unravel and reveal something fascinating. Yeah,
32:55
Speaker 1: humans are annoying like that, you know, never satisfied humans,
32:59
Speaker 1: or physics sists or three year old kids, basically the same.
33:04
Speaker 1: It's one category. It's one category, all right. Well, we
33:06
Speaker 1: hope you enjoyed that and got you to think a
33:08
Speaker 1: little bit about the moon and how it formed and
33:11
Speaker 1: what's out there that we still know every time you
33:14
Speaker 1: go out into the night and look up at the
33:16
Speaker 1: night's car that's right. And if you have questions about
33:19
Speaker 1: something you don't understand and you'd like us to explain,
33:21
Speaker 1: please send them to us at questions at Daniel and
33:24
Speaker 1: Jorge dot com. And if you are a Russian billionaire
33:27
Speaker 1: with disposable income. Let us know that's right. Send it
33:31
Speaker 1: to money at Daniel and Jorge dot com. See you
33:34
Speaker 1: next time. Thanks for tuning in. If you still have
33:44
Speaker 1: a question after listening to all these explanations, please drop
33:48
Speaker 1: us a line. We'd love to hear from you. You
33:50
Speaker 1: can find us at Facebook, Twitter, and Instagram at Daniel
33:53
Speaker 1: and Jorge That's one word, or email us at Feedback
33:57
Speaker 1: at Daniel and Jorge dot com. Thank for listening, and
34:00
Speaker 1: remember that Daniel and Jorge Explain the Universe is a
34:03
Speaker 1: production of I Heart Radio. For more podcast from my
34:06
Speaker 1: Heart Radio, visit the i heart Radio app, Apple Podcasts,
34:10
Speaker 1: or wherever you listen to your favorite shows. H