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How Can We Tell The Distance To Stars? · Daniel and Kelly’s Extraordinary Universe

0:07
Speaker 1: You know, Daniel, sometimes I think how far is everything
0:10
Speaker 1: from us? Like how alone are we? We are nowhere
0:14
Speaker 1: in the universe exactly, or maybe right on the edge
0:17
Speaker 1: of the middle of nowhere. You mean, we're like in
0:19
Speaker 1: the suburbs. That's right. You have to drive pretty far
0:22
Speaker 1: to get somewhere excitings from where we are in the universe.
0:25
Speaker 1: You know, if you look at into the night skuy,
0:27
Speaker 1: it just looks black with little pinpoints, you know, Like,
0:30
Speaker 1: how do we know how far away these things are? Yeah,
0:33
Speaker 1: it's amazing. Some of these things we look at, the
0:35
Speaker 1: nice guy are pretty close by, you know, planets, other
0:37
Speaker 1: things are incredibly distant, you know, billions of light years away.
0:42
Speaker 1: We are sitting on this little ball of rock floating
0:45
Speaker 1: through space, and we are making these huge a statements
0:48
Speaker 1: about the structure of the rest of the entire universe,
0:53
Speaker 1: Like how could we possibly know all this? She's sitting
0:55
Speaker 1: on this little tiny rock. Hi am Jorge, and I'm Daniel,
1:16
Speaker 1: am my cartoonist. I'm a particle physicist. And this is
1:20
Speaker 1: our podcast called Daniel and Jorge Explain the Universe, in
1:24
Speaker 1: which we talk about all the things in the universe
1:27
Speaker 1: and how we understand them. Or if we understand them.
1:31
Speaker 1: Were actually most of the things that we don't understand
1:34
Speaker 1: to be on the podcast, we're going to answer a
1:36
Speaker 1: question from a listener. That's right. Listener Ryan Lynn wrote
1:39
Speaker 1: in with a really interesting question. He said, how do
1:42
Speaker 1: we know what we know? A lot of times in
1:45
Speaker 1: science you hear about an amazing discovery or something science
1:48
Speaker 1: has figured out. But this listener, Ryan always wondered, how
1:51
Speaker 1: do they know that? How they figure that out? How
1:53
Speaker 1: is it possible to know such crazy facts about the
1:56
Speaker 1: universe given that we're stuck on this tiny rock in
1:59
Speaker 1: one the will spot around the in the universe. Yeah,
2:02
Speaker 1: and just for the record, we may or may not
2:03
Speaker 1: have changed his name to protect his identity, and he
2:08
Speaker 1: may or may not live at one two three Question Drive, Atlanta, Georgia,
2:14
Speaker 1: And that's obviously made up. But yeah, if you have
2:16
Speaker 1: any questions at listeners, please send them to us. You
2:19
Speaker 1: can always write us at questions at Daniel and Jorge
2:22
Speaker 1: dot com. So this is a very broad question, how
2:25
Speaker 1: do we know what we know? But he had a
2:27
Speaker 1: very specific example, right, He asked, how do we know
2:34
Speaker 1: how far away the stars are? Yeah, which is a
2:37
Speaker 1: great question because as you look up with the night sky.
2:40
Speaker 1: A lot of the stars look similar, right, they're just
2:42
Speaker 1: pinpoints in the sky. Yeah, And so you might ask, like,
2:45
Speaker 1: how can you tell which ones are close by and
2:47
Speaker 1: which ones are are far away? In fact, your eyes
2:50
Speaker 1: sort of looks like they're all just painted on a
2:52
Speaker 1: ceiling right to your eye, to your brain, they just
2:54
Speaker 1: look like they're painted on a huge dome roof. Yeah,
2:58
Speaker 1: And I think for many thousand and some years that's
3:00
Speaker 1: what people thought. They thought they were looking up essentially
3:03
Speaker 1: the ceiling of their living room, right, and that the
3:06
Speaker 1: stars were painted on them. There's like a show and
3:09
Speaker 1: it's very uh, you know, anthrocentric that suggests that there's
3:12
Speaker 1: something created for us to experience, when in fact, of course,
3:15
Speaker 1: it's a mostly cold, empty universe that ignores and ignores us.
3:19
Speaker 1: I'd love to live in that house where your living
3:21
Speaker 1: room is the size of the cosmos. Right. But that's
3:25
Speaker 1: the thing. They had no idea how big it was, right.
3:27
Speaker 1: They thought the sky was, you know, a few miles
3:30
Speaker 1: or a a few hundred miles up there. They had no
3:32
Speaker 1: concept at the scale of the thing they we're looking at,
3:34
Speaker 1: you know. And that's the crux of the issue, is
3:37
Speaker 1: that when you look up in the night sky, you
3:38
Speaker 1: can't tell if something is really far away and huge
3:41
Speaker 1: or really close by and not actually that big, right,
3:44
Speaker 1: because like if you look out into a landscape, you
3:46
Speaker 1: can see a mountain, and you sort of know how
3:49
Speaker 1: big mountains are, so just kind of by the size
3:51
Speaker 1: of how it looks, you can sort of guess how
3:54
Speaker 1: far away it is, right, But a star is it's
3:56
Speaker 1: like you don't even see it as a circle or
3:58
Speaker 1: a ball or nothing. It's just like a pinpoint of light,
4:01
Speaker 1: that's right. And that applies even for closer up stuff.
4:04
Speaker 1: Like I was talking with my kids about this question yesterday,
4:07
Speaker 1: and I told my daughter, you know that the sun
4:10
Speaker 1: is much much bigger than the Earth, it just looks
4:12
Speaker 1: small because it's far away, And she was surprised. She
4:15
Speaker 1: didn't realize that the Sun was bigger than the Earth.
4:17
Speaker 1: And of course we know now it's much much bigger
4:19
Speaker 1: than the Earth. But in the sky it seems a
4:21
Speaker 1: lot smaller than the Earth, which is huge right in
4:24
Speaker 1: our perspective, But it only looks that way because it's
4:27
Speaker 1: far away. And if you didn't know, like, well, how
4:29
Speaker 1: big is it, then you would have no idea is
4:32
Speaker 1: it enormous and far away or kind of small and
4:35
Speaker 1: close up. Right. Yeah, so this is a good question,
4:38
Speaker 1: and it's not an easy question, right, and it's taken
4:41
Speaker 1: us a while to figure out how to tell how
4:42
Speaker 1: far away stars are. But before we talk about how
4:45
Speaker 1: scientists have done it, we thought we'd ask people on
4:47
Speaker 1: the street if they hadn't in any ideas. Do people
4:50
Speaker 1: know how the distance to far away stars is measured?
4:53
Speaker 1: Or do they just take scientists at their word. Think
4:56
Speaker 1: about it for a moment. You know, how would you
4:58
Speaker 1: tell how far away a star is? Well, here's what
5:01
Speaker 1: people around the U See Irvine campus had to say.
5:04
Speaker 1: I have no idea how to tell that. No, I
5:06
Speaker 1: don't know that at all. You use the telescope, I
5:11
Speaker 1: don't know. Stressed out but sorry, um by some scientific
5:18
Speaker 1: TV show something like that. Okay, yeah, I think so
5:22
Speaker 1: I don't know, like who count we metch with that?
5:24
Speaker 1: I don't know? Actually, okay, okay, So most people had
5:29
Speaker 1: no idea how this is done, which I love, right,
5:32
Speaker 1: And I could see in their faces when I asked
5:34
Speaker 1: them they're all of a sudden they thought, what, wait,
5:37
Speaker 1: that's a good question. I have no idea, not only
5:39
Speaker 1: how you would how scientists do it, but how you
5:42
Speaker 1: would even do it right? Most of the people reacted
5:44
Speaker 1: that way. It's all familiar words. You know, how far
5:47
Speaker 1: away something? Stars? Who know stars? But when you think
5:50
Speaker 1: about it, like, it's really not that intuitive to know
5:53
Speaker 1: how far away stars? Yeah, it's not that easy, though.
5:56
Speaker 1: I love that some people had ideas, like one guy's like, well,
5:58
Speaker 1: just watch scientific television shows and we'll tell you. Just
6:01
Speaker 1: listen to a podcast. I mean, that's what scientists do, right,
6:04
Speaker 1: you wanted the answer to question, just just turn on
6:06
Speaker 1: science TV and listen for the answer. Then you write
6:09
Speaker 1: it up in the paper. It's like a snake eating
6:11
Speaker 1: its own tail. That's how all science has done. But
6:15
Speaker 1: the point is that it's not an easy problem and
6:17
Speaker 1: that most people don't know the answer. Yeah, maybe we
6:23
Speaker 1: should start by talking about things that are close up,
6:25
Speaker 1: Like how do we tell how far away things are? Well,
6:28
Speaker 1: we have two eyes, right, So say, for example, Uh,
6:32
Speaker 1: somebody's throwing a basketball at you. How do you know
6:34
Speaker 1: how far away the basketball is? Well, one thing is
6:37
Speaker 1: you know how big a basketball should be, So as
6:40
Speaker 1: it gets bigger, you're imagining it's getting closer. But say
6:43
Speaker 1: somebody throws something at you you've never seen before, you're
6:45
Speaker 1: not familiar with. Right, has your brain know how far
6:48
Speaker 1: away it is? The key is that you have two
6:50
Speaker 1: eyeballs and not just one. Yeah, so you you your
6:53
Speaker 1: brain looks at the difference between what your left eye
6:56
Speaker 1: and your right eye are seeing. Right. Yeah, you have
6:59
Speaker 1: to do this experiment. Hold out one finger in front
7:01
Speaker 1: of your face and then look at it with your
7:04
Speaker 1: left eye only and then your right eye only, and
7:07
Speaker 1: you'll see it move right. You get two different images,
7:10
Speaker 1: and you see a little bit different. You see a
7:12
Speaker 1: little bit more of one side of the finger with
7:13
Speaker 1: one eye and a little bit more of the other
7:15
Speaker 1: side of the finger with the other eye. Right, so
7:17
Speaker 1: you get its binocular vision right binocular meaning two eyes.
7:21
Speaker 1: You get binocular vision, and your brain compares these two pictures.
7:25
Speaker 1: And if these two pictures are really different, that means
7:27
Speaker 1: the thing is pretty close, right, because you're looking at
7:30
Speaker 1: the thing from very two very different angles. Um, only
7:33
Speaker 1: if it's really close. But now move your finger as
7:37
Speaker 1: far away as your arm will allow. Right. Please don't
7:39
Speaker 1: chop off your finger and throw a bast room or
7:45
Speaker 1: over driving. Then you do this as a mental exercise.
7:48
Speaker 1: Please or pull over. Yeah, So now with your finger
7:51
Speaker 1: further away, do the same thing where you look at
7:54
Speaker 1: it only with one eye or the other, and you'll
7:55
Speaker 1: you'll notice that the two images look more similar. And
7:59
Speaker 1: as your finger gets further and further away, the two
8:01
Speaker 1: images look more and more similar. Something that's really really
8:04
Speaker 1: far away looks the same to both eyes, right, because
8:07
Speaker 1: the distance between your eyes gets really small compared to
8:11
Speaker 1: the distance to the object. Yeah, and it's more noticeable
8:15
Speaker 1: if you switch eyes very quickly, right, Like, if you
8:17
Speaker 1: go blink blink, blink, blink, blink, switch between eyes, you
8:20
Speaker 1: can really see how things change the closer they are too,
8:23
Speaker 1: that's right. It also kind of makes you look like
8:24
Speaker 1: a crazy person. So if you're listening to this podcast
8:27
Speaker 1: out in public, you know, maybe get a little privacy.
8:29
Speaker 1: I'd love to imagine there's some some car pulled over
8:32
Speaker 1: by this side of the road with a person blinking
8:36
Speaker 1: back and forth, and somebody is now calling Homeland Security
8:40
Speaker 1: saying because of somebody's suspicious behavior. Right, let's take a
8:45
Speaker 1: quick break. So yeah, that's called parallel right, which is
9:01
Speaker 1: is not a comic book villain. It's like an actually,
9:06
Speaker 1: oh man, this should totally be a comic book villain
9:08
Speaker 1: with like lots of sets of eyeballs or something. Parallax. Yeah,
9:12
Speaker 1: that's um, that's called binocular vision, right end, or parallax.
9:16
Speaker 1: And the idea there is that you see from different
9:18
Speaker 1: angles if you have two views of it. So that
9:20
Speaker 1: works for your eyeballs because they're spaced, um fairly, there
9:24
Speaker 1: is space fairly wide. Right, It's kind of like a triangle, right,
9:27
Speaker 1: Like if you draw a line between your eyes and
9:29
Speaker 1: then another line from each of your eyes to the object,
9:32
Speaker 1: you form a triangle, right, And that's how you it's
9:35
Speaker 1: called triangulation for because then with the triangle, you can
9:39
Speaker 1: tell how far away it is, that's right. And that's
9:41
Speaker 1: why if you lose an eye or close an eye,
9:43
Speaker 1: you don't have very good depth perception, right, because you
9:46
Speaker 1: need both of those views to see how far away
9:48
Speaker 1: things are. So people with one eye or people with
9:50
Speaker 1: an eye Patriot ever, you know, they stumble more often
9:53
Speaker 1: for this reason, and they have developed other techniques for
9:55
Speaker 1: knowing how far away things are. So that also works
9:59
Speaker 1: for the stars, right, and maybe you're thinking a whole
10:02
Speaker 1: lot of second, the stars are super duper far away, right,
10:05
Speaker 1: My eyes can't measure the distance to a mountain. How
10:08
Speaker 1: can my eyes measure the distance to the stars? It
10:11
Speaker 1: seems almost impossible. Well, what's happening when I look at
10:14
Speaker 1: the stars with my naked eye? Like, why can't I
10:16
Speaker 1: just resolve the use the same technique? Right? And the
10:20
Speaker 1: reason is that the distance to the stars compared to
10:23
Speaker 1: the distance between your eyes is almost infinite. Right, that
10:26
Speaker 1: triangle you talked about a tiny little side which is
10:30
Speaker 1: the distance between your eyes, and then you know the
10:33
Speaker 1: other two sides that extend all the way to the stars.
10:36
Speaker 1: It's like light years and light years and light years.
10:38
Speaker 1: So basically those photons are parallel to each other, right,
10:42
Speaker 1: And do you see the same image? Technically your eyes
10:45
Speaker 1: see different images. It's just that maybe the difference is
10:48
Speaker 1: so small your brain and your eyeball can't tell the
10:52
Speaker 1: difference exactly. So in theory, if you had super duper vision,
10:57
Speaker 1: then maybe you could use that information to tell the
11:00
Speaker 1: distance to the stars. Or if your eyes were really
11:02
Speaker 1: really far apart exactly, if your eyes are really far apart,
11:06
Speaker 1: or you have really really good vision, those are two
11:08
Speaker 1: ways to make this distance measurement measurement more possible. So
11:11
Speaker 1: that's exactly what we do to make our eyes further apart.
11:14
Speaker 1: We don't just look at the star up at the
11:17
Speaker 1: night sky. We wait for the Earth to go around
11:20
Speaker 1: the Sun, and we look at the star from both
11:22
Speaker 1: sides of the Sun. So, you know, you look at
11:24
Speaker 1: the star in in June and you're one side of
11:27
Speaker 1: the Sun, and then the Earth goes around the Sun.
11:30
Speaker 1: You look at the same star in December. Now you're
11:33
Speaker 1: looking at the star from two astronomical units apart, right,
11:37
Speaker 1: as if your eyeballs were two astronomical units apart, right
11:41
Speaker 1: opposite sides of the Sun. So that's pretty good distance. Yeah,
11:45
Speaker 1: it's like in December you open your right eye and
11:48
Speaker 1: you look at the star, and in June you open
11:50
Speaker 1: your left eye and you look at the star, and
11:51
Speaker 1: you compare how those two images are different. That's right.
11:54
Speaker 1: And I hope that you have things to do between
11:56
Speaker 1: December and June other than just standing outside waiting for
11:59
Speaker 1: six months to open and the other isn't that? I thought?
12:03
Speaker 1: It depends on how devoted you are to science, you know,
12:06
Speaker 1: like people, if you really care about this stuff. No,
12:08
Speaker 1: that's exactly what it's like. And um, so you take
12:11
Speaker 1: one piece of data in one part of the year,
12:12
Speaker 1: and the other piece of dating the other part of
12:14
Speaker 1: the year, and that's effectively like making your head you
12:17
Speaker 1: know the size of the solar system, and so that's
12:20
Speaker 1: a huge additional leverage Toto seeing things that are really
12:24
Speaker 1: far away. I wonder if that's how they measured how
12:27
Speaker 1: far the moon was, do you know what I mean?
12:29
Speaker 1: Like maybe not waiting, waited until a whole half year,
12:33
Speaker 1: but just kind of like looked at the moon, talk
12:36
Speaker 1: to somebody who was a couple of miles away and
12:38
Speaker 1: see what the what the difference between what he saw
12:40
Speaker 1: and you saw That would tell you how far away
12:42
Speaker 1: the moon is. Right, Well, there's a couple of things there.
12:44
Speaker 1: One is them waiting part of the year won't help
12:47
Speaker 1: you with the moon because the moon moves with the Earth, right,
12:49
Speaker 1: we don't leave the moon behind. And the Moon is
12:51
Speaker 1: actually so close up that you can do cool stuff
12:53
Speaker 1: like bounce a laser off the moon or bounce radio
12:56
Speaker 1: waves off the moon, and to measure the distance, that's
12:59
Speaker 1: actually the best way to measure the distance to the moon.
13:02
Speaker 1: And what they've discovered actually is that the Moon is
13:05
Speaker 1: getting further and further every every year. We're losing the moon,
13:09
Speaker 1: like the Moon is orbiting the Earth. But what orbit
13:12
Speaker 1: grows very gradually? Yeah, when when are we going to
13:15
Speaker 1: lose the moon? Let's see what time is it now?
13:18
Speaker 1: You know, um, it's gonna be a long time. We're
13:20
Speaker 1: gonna have the Moon around for a while. You don't
13:21
Speaker 1: have to worry about it. And if you bought real
13:23
Speaker 1: estate on the Moon, you're fine. But I think by
13:26
Speaker 1: a centimeter of years is the number. I remember. The
13:29
Speaker 1: distance from the Earth to the Moon is growing. That's
13:31
Speaker 1: not nothing. That's not nothing. But also the astronauts put
13:34
Speaker 1: mirrors on the Moon when they landed there so that
13:36
Speaker 1: we can shine lasers at those mirrors and do cool
13:39
Speaker 1: tests stuff like a global selfie. That's exactly right. Yeah,
13:45
Speaker 1: And so so we're saying, if you want to get
13:48
Speaker 1: better measurements of UM using this parallax system, you either
13:51
Speaker 1: need to have your eyes further apart and when you
13:53
Speaker 1: do that is so the June and December, or you
13:55
Speaker 1: need better eyes. So, of course we don't just use
13:58
Speaker 1: my eyeballs or Jorges eyeballs or my students eyeballs. We
14:01
Speaker 1: use telescopes and telescopes out in space that can tell
14:05
Speaker 1: the difference between really really small images, right, that can
14:08
Speaker 1: look really really far away and measure very precisely where
14:12
Speaker 1: these stars are at different times of the year. Yeah,
14:15
Speaker 1: I just think it's amazing that you can see something
14:18
Speaker 1: so far away. You know, like here on Earth, you're
14:20
Speaker 1: used to far away things looking blurry or faded or faint.
14:24
Speaker 1: But just the idea that you know, millions trillions of
14:27
Speaker 1: light years away, you know, a photon left the star,
14:31
Speaker 1: traveled throughout the entire cosmos and then arrived into your eyeball,
14:36
Speaker 1: right when you're looking at the night sky. That's one
14:37
Speaker 1: of my favorite things of the night sky is that
14:39
Speaker 1: it's the world's greatest view. It's the universe is greatest view.
14:44
Speaker 1: You know, you are seeing across billions of light years
14:46
Speaker 1: of space. It's it's amazing to me. I totally agree
14:49
Speaker 1: that those photons traveled unimpeded for so long and then
14:52
Speaker 1: finally just get absorbed by your eyeball and then you
14:54
Speaker 1: just a little a glance away, you know. Okay, So
14:57
Speaker 1: then what are other ways? How do we tell how
15:00
Speaker 1: are weight things are beyond a few thousand light years? Well,
15:03
Speaker 1: that's really the best method we have, is this parallax method.
15:06
Speaker 1: And so science has been working on that really hard,
15:08
Speaker 1: and it's actually cool because our ability to do this
15:12
Speaker 1: is improving pretty rapidly. It used to be we could
15:14
Speaker 1: only see things to like maybe a thousand of thousand
15:16
Speaker 1: light years away, and then we've got better telescopes and
15:19
Speaker 1: navigate they see things pretty reliably up to several thousand
15:22
Speaker 1: light years, And now that we have even better telescopes,
15:25
Speaker 1: we're seeing some things up to like ten fifteen thousand
15:28
Speaker 1: light years away. So as we get better and better telescopes,
15:31
Speaker 1: we're gonna get better and better measurements of this than
15:33
Speaker 1: Parallax is really the crux. That's the way that we
15:36
Speaker 1: really believe that it gives us the most reliable estimates
15:40
Speaker 1: of distance, so everything is built on that. Beyond that,
15:43
Speaker 1: when things are further away, then there's you know, fuzziness,
15:48
Speaker 1: there's questions and people out there might get a little
15:50
Speaker 1: skeptical and how do we know some of these things?
15:52
Speaker 1: But essentially what you need to do is what we
15:54
Speaker 1: talked about earlier, is find something that's a reference point.
15:57
Speaker 1: Find something where you know how bright it is, so
16:00
Speaker 1: you can tell like a mountain, like, you know how
16:02
Speaker 1: big amountain typically is. Yeah exactly. Um, yeah, So if
16:07
Speaker 1: you if somebody was, for example, standing on a mountain
16:09
Speaker 1: and shining a really bright light, and you knew how
16:12
Speaker 1: bright that light was at the source, then you could
16:15
Speaker 1: measure how dim it is where you are, and you
16:17
Speaker 1: could tell the distance, right, because the brightness falls like
16:21
Speaker 1: one over the distance squared, because the photons go out
16:24
Speaker 1: in every direction, and the surface area of a sphere
16:27
Speaker 1: around the star goes like radius squared, and so the
16:30
Speaker 1: same amount of light is spread over more and more areas.
16:34
Speaker 1: You just get fewer of those photons the further away
16:36
Speaker 1: you are, even if with no atmosphere, no air between you,
16:39
Speaker 1: that's right, things just spread out. And so, as you said,
16:42
Speaker 1: we get just a little stream of those photons. Most
16:44
Speaker 1: of the photons from stars are going somewhere else, right,
16:47
Speaker 1: something somewhere else in the universe, and eyeball, we hope
16:50
Speaker 1: is picking up one of those photons. So we're only
16:52
Speaker 1: seeing a tiny little slice of the photons that come
16:55
Speaker 1: from that star. So, as we were saying, if you
16:58
Speaker 1: want to know how far aways something is, you have
17:00
Speaker 1: to know how bright it was originally, how bright it
17:02
Speaker 1: is at the source, and then compare that to the
17:04
Speaker 1: brightness you're measuring on Earth. That's pretty tricky because the
17:07
Speaker 1: universe is filled with weird stuff that we don't understand, right,
17:10
Speaker 1: and so it's sort of chicken and egg, Right, you
17:12
Speaker 1: want to know how far away is that stuff? When
17:14
Speaker 1: what is it? Well, you don't know either one. You're
17:17
Speaker 1: you're sort of in a in a pinch. It just
17:18
Speaker 1: looks like little dots. It just looks like little dots.
17:21
Speaker 1: But we found a few things that we can use
17:23
Speaker 1: for reference points. But maybe let's take a break and
17:26
Speaker 1: we can dig into that in a moment. Okay, So
17:40
Speaker 1: what are the other ways we can tell how far
17:42
Speaker 1: away stars are? So one of the ways is with
17:44
Speaker 1: these really weird kind of stars that are variable stars
17:48
Speaker 1: that don't shine the same amount of brightness all the time.
17:51
Speaker 1: And the reason is that, well, there's some really complicated
17:54
Speaker 1: astrophysics that's beyond me, frankly. But the thing that's important
17:57
Speaker 1: to know these stars, which are called sapid's um, they pulsate,
18:02
Speaker 1: and the rate at which they pulsate is very closely
18:05
Speaker 1: connected to their brightness. So if you can measure how
18:09
Speaker 1: fast they are pulsating, you can know their brightness. It's
18:13
Speaker 1: got this internal layer that stores and releases energy so
18:16
Speaker 1: that the whole star expands and contracts, and that's what
18:20
Speaker 1: makes it pulsate, kind of like a lighthouse. Yeah, just
18:22
Speaker 1: like a lighthouse exactly. Um, it's just like a lighthouse.
18:26
Speaker 1: So these things are like lighthouses out there in in
18:28
Speaker 1: our galaxy and in other galaxies. And people figured out
18:32
Speaker 1: by using parallax that the ones that are pretty close
18:35
Speaker 1: up that there's a relationship between how bright they are
18:38
Speaker 1: and how fast they pulsate. And that's really cool because
18:42
Speaker 1: then there are ones that are really far away where
18:44
Speaker 1: we can't use parallax to tell how far away they are,
18:47
Speaker 1: but we can tell how fast they are pulsating. Right,
18:50
Speaker 1: that's not hard to measure. You just watch it and
18:52
Speaker 1: you see blink on and off. You can then say,
18:55
Speaker 1: you know how bright it is at the source. You
18:58
Speaker 1: know how bright it is at the source, and you
19:00
Speaker 1: know how bright it is here on Earth. Then you
19:02
Speaker 1: can do some simple math to figure out how far
19:04
Speaker 1: away it must be. Like it's telling you using Morse
19:07
Speaker 1: code how bright it is, right, Like it's like I'm
19:10
Speaker 1: really right, I'm really dim yeah, and so and that's
19:13
Speaker 1: the key. These things are called standard candles, and they're
19:16
Speaker 1: just ways to know how bright something is at the
19:19
Speaker 1: source without knowing how far away it is, right, that's
19:22
Speaker 1: the key. You have to have some other way of
19:24
Speaker 1: knowing how bright they are. And so these were discovered,
19:27
Speaker 1: you know, almost a hundred years ago, and it was
19:30
Speaker 1: Hubble himself, Edwin Hubble, who used these and found them,
19:33
Speaker 1: a bunch of them that were surprisingly far away. He
19:36
Speaker 1: looked up in the night sky, and back then people
19:38
Speaker 1: thought the whole universe was just the Milky Way Galaxy.
19:41
Speaker 1: That was it. You know, there was just a bunch
19:43
Speaker 1: of stars and we are galaxy and nothing else right
19:46
Speaker 1: like there was it was all concentrated around us. Yeah,
19:49
Speaker 1: they thought that was the whole universe. And you know,
19:50
Speaker 1: even that was mind blowing to people. Right If if
19:53
Speaker 1: all you thought was, oh, it's just just the Earth
19:55
Speaker 1: and a few other planets and everything else is sort
19:57
Speaker 1: of painted on the living room of the sky, then
19:59
Speaker 1: it's mind blowing to think, what, there's a whole galaxy
20:02
Speaker 1: of zillions of stars, right. So people were just are
20:05
Speaker 1: slowly accepting that. And then Hubble he looked to try
20:09
Speaker 1: to measure these these syfids and see how far away
20:12
Speaker 1: they were, and he got some really weird results. He
20:14
Speaker 1: got results that suggested that these things were crazy far away,
20:18
Speaker 1: far away than any star anybody has seen before, and
20:21
Speaker 1: so we thought, well, maybe these things are not just
20:24
Speaker 1: like weird nebula or weird other stars. Maybe there are
20:27
Speaker 1: other galaxies. And that must have been a mind blowing
20:30
Speaker 1: moment for him, Right, Wow, It's like, it's not just
20:33
Speaker 1: us in our living room, there's other houses around us, exactly, exactly.
20:38
Speaker 1: And that's what I love about this question is figuring
20:41
Speaker 1: out how far away the stars is, gives us a
20:44
Speaker 1: three D map of the universe, right, tells us where
20:47
Speaker 1: everything is, what is the structure where we living, Like,
20:50
Speaker 1: are we in the suburbs? Are we in the exciting
20:52
Speaker 1: downtown hip area of the universe? Right? So it's so important,
20:55
Speaker 1: and it's exactly what's led to these moments of realization
20:59
Speaker 1: where you discover or that the universe is totally different
21:02
Speaker 1: from the way you thought it was. I hope to
21:04
Speaker 1: I hope to have one of those moments myself in
21:05
Speaker 1: my science career. It's it's let us map the universe
21:08
Speaker 1: and where we are in exactly. That's a big exactly,
21:11
Speaker 1: that's a huge deal. And that really was the birth
21:14
Speaker 1: of modern cosmology. You know, knowing there were other galaxies
21:18
Speaker 1: and wondering how many are there and how did this
21:20
Speaker 1: all come together? And you know, and obviously if there
21:23
Speaker 1: are other galaxies, then maybe we're not the most important
21:25
Speaker 1: one or at the center of anything or all those
21:28
Speaker 1: questions were created just at that moment when we discovered
21:30
Speaker 1: that there were other galaxies. Okay, so that's a really
21:37
Speaker 1: cool trick is find an astronomical object that somehow tells
21:42
Speaker 1: you how bright it is, not by how bright it is,
21:44
Speaker 1: but through some other information. Yeah, exactly, and so you
21:48
Speaker 1: have to really know the astrophysics of it. And the
21:50
Speaker 1: cepheids were calibrated by comparing to the parallax scale, So
21:55
Speaker 1: parallax works up to you know, maybe ten tho light years,
21:57
Speaker 1: and in that sphere there are some of these stars,
22:00
Speaker 1: these variable stars. Once you know that, then you can
22:03
Speaker 1: look at the ones even further out using this technique
22:06
Speaker 1: exactly exactly. An astronomers call this the cosmic distance ladder.
22:10
Speaker 1: Because there's a bunch of different techniques that use for
22:12
Speaker 1: things at different distances, and then you try to overlap
22:15
Speaker 1: them and stitch them together. There's no one technique that
22:17
Speaker 1: will work for everything really close up stuff. You've got
22:20
Speaker 1: parallax for stuff that's a little further away. You got
22:23
Speaker 1: these these variable stars, the cfids, and then after that
22:26
Speaker 1: you have to use GPS. After that you just watch
22:30
Speaker 1: a science TV show that you have to do everything. Um,
22:34
Speaker 1: the problem is that cefids are just stars, and so
22:37
Speaker 1: they're bright, but they're not that bright and you want
22:39
Speaker 1: to see something like in another galaxy or really really
22:42
Speaker 1: far away galaxies. You can't resolve individual stars in super
22:46
Speaker 1: duper far away galaxies, so that has a limit to Yeah,
22:50
Speaker 1: so then they needed something super crazy bright to serve
22:53
Speaker 1: as a standard candle for the rest of the universe
22:56
Speaker 1: because these stars, even though they blink, they get lost
23:00
Speaker 1: in the light from the rest of the galaxy they're in. Yeah, exactly,
23:04
Speaker 1: they're not particularly bright kind of stars, and so that's
23:07
Speaker 1: why the end of the cosmic distance Ladder is dominated
23:11
Speaker 1: by supernova. Supernova is when a star goes boom, right
23:15
Speaker 1: when it's time to check out. It's had all of
23:18
Speaker 1: its fun and it's decided we're done with all this
23:20
Speaker 1: fusion stuff. Let's just blow it on one last big party.
23:23
Speaker 1: It collapses basically right like it runs out of fuel
23:26
Speaker 1: and then it just yeah, and we did a whole
23:29
Speaker 1: fun podcast episode on house stars and their lives um
23:32
Speaker 1: which you should go out and listen to you're interested
23:34
Speaker 1: in that kind of detail. But the critical thing is
23:36
Speaker 1: that one kind of star ends in a very particular way,
23:40
Speaker 1: and it's called a type one a supernova, and the
23:42
Speaker 1: supernova are extraordinarily bright. The thing you have to understand
23:45
Speaker 1: is that the stars like using up all of its
23:48
Speaker 1: fuel in a very short amount of time, and so
23:51
Speaker 1: it's extremely bright, and a single supernova can be brighter
23:55
Speaker 1: than the entire galaxy that it's in. So that's how
23:57
Speaker 1: we can see it. I mean, if you look at
23:59
Speaker 1: the night sky, you can see these these little fuzzy
24:02
Speaker 1: things that are the other galaxies, but you can't really
24:04
Speaker 1: resolve any particular star in it right. Well, for the
24:07
Speaker 1: close up ones you can, like for Andromeda, which is
24:10
Speaker 1: whe of the nearest galaxies, you can see the shape
24:11
Speaker 1: of it, you can see individual stars, but you're right.
24:13
Speaker 1: For the furthest ones, they're just little smudges and you
24:16
Speaker 1: can't resolve individual stars except when one of them goes boom,
24:20
Speaker 1: and then you can see it and it's brighter than
24:22
Speaker 1: the hundred billion stars combined. Right. That's it's incredible to
24:26
Speaker 1: me how bright these supernov are. And you don't want
24:29
Speaker 1: to be close to any of these things, right, any
24:31
Speaker 1: Anybody near these things gets instantly sterilized. So we would
24:35
Speaker 1: see it as a like a little dot in the
24:37
Speaker 1: inside of a galaxy which is flash like it will
24:40
Speaker 1: just yeah, And in the night sky you see it
24:43
Speaker 1: as maybe a new star. Right. There could be like
24:45
Speaker 1: a little smudge there you never noticed from a really
24:47
Speaker 1: far away galaxy, and all of a sudden, there's a
24:49
Speaker 1: bright star there. And you can look back in history
24:52
Speaker 1: and see the record where ancient people's saw these things
24:55
Speaker 1: in the night sky. Right, we have a history of
24:57
Speaker 1: supernov explosions that goes back more than a thou and
25:00
Speaker 1: years because like Chinese astronomers are noticed, hey, on this date,
25:04
Speaker 1: a new star appeared in this guy and the only
25:06
Speaker 1: lasted for three weeks and then it was gone. Boy,
25:08
Speaker 1: that was weird. And the trick is that these supernova
25:11
Speaker 1: are always the same, right, It's not like do you
25:14
Speaker 1: have small supernovas and big supernovas. It's like, if you're
25:17
Speaker 1: gonna have a supernova, it's always this bright. Well, there
25:21
Speaker 1: are a lot of different kinds of supernova. But this
25:23
Speaker 1: one kind, called Type one A always has the same
25:26
Speaker 1: sort of curve, this light curve when we talk about
25:28
Speaker 1: how bright it gets and then it hits a peak
25:30
Speaker 1: brightness and then dims away, and the whole process last days.
25:34
Speaker 1: But it always has the same shape and always has
25:37
Speaker 1: the same peak brightness. Now, for those of you who
25:40
Speaker 1: know a lot about this, there are some technical details
25:42
Speaker 1: and in the variation of the peak brightness, but that
25:44
Speaker 1: can get calibrated away, and we can talk about that
25:47
Speaker 1: another time. But the basic version of the story is
25:49
Speaker 1: that they always have the same peak brightness because it's
25:52
Speaker 1: always the same kind of process. It's always the same
25:55
Speaker 1: size star with the same amount of fuel in it.
25:58
Speaker 1: It's not like every star those supernova. It's like only
26:01
Speaker 1: once with a particular size and stuff, and it will
26:04
Speaker 1: collapse at some point right in a very particular way.
26:07
Speaker 1: That's exactly right. There's lots of different kinds of supernova,
26:09
Speaker 1: but one kind which comes from binary star systems, in
26:13
Speaker 1: which one of them is a white dwarf that leads
26:16
Speaker 1: to Type one A supernova, and which just happens to
26:19
Speaker 1: be very regular, and it happens to be very little
26:21
Speaker 1: variation between the brightness of different type one A supernova.
26:26
Speaker 1: And this is something people realized, you know, like twenty
26:29
Speaker 1: thirty years ago, but it took some work. You know,
26:32
Speaker 1: people are constantly out there looking for new ways to
26:35
Speaker 1: find distance metrics, new ways to figure out how far
26:38
Speaker 1: away things are. And people we're working on Type one
26:41
Speaker 1: A supernova and other people working on this kind of thing.
26:44
Speaker 1: So people work on the other kind of thing. People
26:46
Speaker 1: today right now are working on new ways to measure
26:48
Speaker 1: distances because we always want to know more precise information.
26:51
Speaker 1: So behind the scenes, grad students were slogging away, can
26:55
Speaker 1: we figure out how far away type and supernova are?
26:57
Speaker 1: Can we calibrate they're they're like her, so that they
27:00
Speaker 1: all look the same. And then about in the late nineties,
27:04
Speaker 1: people figured out how to do it, and the technology
27:06
Speaker 1: became possible and they started collecting this information, right, and
27:10
Speaker 1: so all of a sudden, a whole new window into
27:12
Speaker 1: the universe. We could tell how far away things that
27:14
Speaker 1: are super far away we're because the supernova are so bright. Right,
27:18
Speaker 1: But it's sort of interesting because it came from kind
27:20
Speaker 1: of a random occurrence in the universe, right, Like people
27:23
Speaker 1: just cataloging and observing supernova just for the sake of science.
27:27
Speaker 1: Suddenly they realized that this gives us a tool for
27:31
Speaker 1: mapping the universe exactly. And that's what astronomy is all about.
27:34
Speaker 1: It is like, let's figure out how to use the
27:36
Speaker 1: idiosyncrasies of the universe to give ourselves clues, right, And
27:41
Speaker 1: so yeah, it's just luck, right, I mean, I mean
27:43
Speaker 1: it's luck. What is it revealing that we underneed the
27:46
Speaker 1: surface exactly? That is that is pure science right there.
27:49
Speaker 1: It's like, let's nail down facts about the universe by
27:53
Speaker 1: things that accidentally reveals to us. I mean, everything the
27:56
Speaker 1: universe tells us is an accident, right, nobody's purposely sending
27:59
Speaker 1: us information. We're just a sit unless we're living in
28:04
Speaker 1: a simulation, in which case everything is on purpose. Um. Yeah,
28:08
Speaker 1: So Type one A supernova stand out really really far.
28:10
Speaker 1: The best distance measurements we have come from type one
28:13
Speaker 1: A supernova. So this sort of three step louder there.
28:16
Speaker 1: There's the parallax for close up stuff, the cepids for
28:19
Speaker 1: medium range stuff, and then the type one A supernova
28:22
Speaker 1: for super far away stuff. And you know they overlap,
28:24
Speaker 1: which allows us to calibrate. And it's built one on
28:28
Speaker 1: top of the other, right, like what we know from
28:30
Speaker 1: supernovas is built on what we know from these blinking stars,
28:34
Speaker 1: which is built on what we know about from parallax,
28:38
Speaker 1: which is built on our eyeballs. That's right, exactly, it's
28:41
Speaker 1: built on our listeners eyeballs. And now we actually have
28:47
Speaker 1: a new way to measure distance, which is really cool,
28:50
Speaker 1: which has only been possible recently, and that's um from
28:53
Speaker 1: gravitational waves. Gravitational waves are these ripples in space time
28:58
Speaker 1: that we can measure by seeing how these observatories shrink
29:02
Speaker 1: and expand by my new distances as the gravitational wave passes.
29:08
Speaker 1: And just like with type one A supernova or with cepheids,
29:12
Speaker 1: we know something about the strength of the gravitational wave
29:16
Speaker 1: based on what it looks like here, based on not
29:19
Speaker 1: on its brightness, but like on how fast it's wiggling,
29:22
Speaker 1: because because gravitational waves wiggle right there waves of space,
29:26
Speaker 1: so something about how they're wiggling gives you a clue
29:28
Speaker 1: as to how bright, how intense they were at the source.
29:31
Speaker 1: And then we can by measuring how the intense they
29:34
Speaker 1: are here, we can tell how far away things were.
29:36
Speaker 1: So this is a whole new handle. We only recently
29:39
Speaker 1: added to our cosmic distance ladder. You sound pretty excited
29:43
Speaker 1: about gravitational waves. Um, I am, I am. It's a
29:48
Speaker 1: it's a heavy topic. Um, but it's sort of cool.
29:52
Speaker 1: I guess just taking a step back just to think
29:54
Speaker 1: that we went from like a two D v of
29:56
Speaker 1: the universe just looking at these things that we thought
29:58
Speaker 1: we're painting on the ceiling, to this now really sort
30:01
Speaker 1: of incredibly rich and deep three D conception of the
30:07
Speaker 1: entire cosmics. Right, It's absolutely incredible, and it's more than
30:10
Speaker 1: three D. Actually, it's actually kind of like four D
30:13
Speaker 1: because when we look out into space, we don't just
30:16
Speaker 1: look at it where things are. We look at where
30:18
Speaker 1: things used to be, right, so we see things in
30:21
Speaker 1: sort of these spheres, like the things that are nearby
30:23
Speaker 1: are recent, things that are far away are old. And
30:26
Speaker 1: so we're not just looking out at where we are
30:29
Speaker 1: in the universe like a three D map. We're looking
30:31
Speaker 1: at these shells that get further and further back in time,
30:35
Speaker 1: and so this allows us to see what the universe
30:38
Speaker 1: used to be like, so absolutely gives us a sense
30:40
Speaker 1: for the structure the universe, but also gives us a
30:42
Speaker 1: sense for how that structure is changing, and why you
30:45
Speaker 1: cannot get more rich information about the formation of the
30:48
Speaker 1: universe in our context and why we're here and all
30:51
Speaker 1: that crazy important stuff. Then understanding how the universe came
30:54
Speaker 1: to be the way it is, right, all that just
30:58
Speaker 1: from looking up. That's right. So next time you're looking
31:01
Speaker 1: at the night sky, wonder is there more information there
31:04
Speaker 1: that I'm seeing? If they're more information than even scientists know. Bobile,
31:08
Speaker 1: future scientists laugh at us for missing what's going to
31:11
Speaker 1: be in those futures science shows what's going to be
31:14
Speaker 1: on a future science podcast. All right, thank you very
31:17
Speaker 1: much for listening, and thank you to Ryan for sending
31:19
Speaker 1: this question. Thanks for listening, See you next time. If
31:30
Speaker 1: you still have a question after listening to all these explanations,
31:33
Speaker 1: please drop us a line. We'd love to hear from you.
31:36
Speaker 1: You can find us at Facebook, Twitter, and Instagram at
31:39
Speaker 1: Daniel and Jorge that's one word, or email us at
31:42
Speaker 1: Feedback at Daniel and Jorge dot com.