Latest / Daniel and Kelly’s Extraordinary Universe / What did the night sky look like to the dinosaurs?

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What did the night sky look like to the dinosaurs? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Daniel, how's it going.
• 0:10
  Speaker 2: I'm good.
• 0:11
  Speaker 3: Good.
• 0:11
  Speaker 2: Nice to talk to you again.
• 0:12
  Speaker 1: Yeah, nice to talk to you too. You know, I
• 0:14
  Speaker 1: was out the other day and one of the great
• 0:16
  Speaker 1: things about living in the country is that when there's
• 0:19
  Speaker 1: a cloudless sky, you really get to look up at
• 0:22
  Speaker 1: the stars and see all the night sky. And I've
• 0:25
  Speaker 1: been looking out there with my oldest kiddo lately, and
• 0:29
  Speaker 1: I was wondering, do you and your kids like looking
• 0:31
  Speaker 1: up at the stars too?
• 0:32
  Speaker 2: You know, I'm more into astronomy than they are, but
• 0:35
  Speaker 2: back when they were younger, we did a lot of
• 0:37
  Speaker 2: star watching.
• 0:38
  Speaker 1: Awesome, So you asked a lot of questions, and so
• 0:40
  Speaker 1: I wonder if your kids are like you, do they
• 0:43
  Speaker 1: ask you some really cool questions?
• 0:45
  Speaker 2: They did, yes, sometimes some surprising questions and sometimes some
• 0:48
  Speaker 2: kind of like embarrassing questions.
• 0:50
  Speaker 1: Embarrassing what could possibly be embarrassing about the night sky?
• 0:54
  Speaker 2: Well, I remember telling them that the stars are really old,
• 0:58
  Speaker 2: like super duper old, like crazy old, okay, And then
• 1:03
  Speaker 2: their follow up question was, oh, really old? You mean
• 1:06
  Speaker 2: like you and mommy?
• 1:07
  Speaker 1: Oh out, kids are cruel, I know.
• 1:12
  Speaker 2: So I had to explain to them that we were
• 1:14
  Speaker 2: incredibly old, but not like astronomically cosmically old, not quite yet.
• 1:20
  Speaker 1: It's a different scale entirely.
• 1:22
  Speaker 4: Really.
• 1:38
  Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor
• 1:41
  Speaker 2: at UC Irvine, and I like to think of myself
• 1:44
  Speaker 2: as not astronomically old.
• 1:46
  Speaker 1: I'm Kelly Wiener Smith. I'm adjunct at Race University. And
• 1:50
  Speaker 1: my daughter asked the other day when I couldn't hear
• 1:53
  Speaker 1: what she was saying, if that was because I was
• 1:55
  Speaker 1: getting old, and sometimes old people lose their hearing. I
• 1:58
  Speaker 1: also prefer to think of myself is not astronomically old,
• 2:01
  Speaker 1: but maybe old by people's standards. Who knows.
• 2:04
  Speaker 2: And so, what did you say? Did you say? Huh?
• 2:06
  Speaker 5: What?
• 2:06
  Speaker 2: I didn't hear you?
• 2:09
  Speaker 1: Now I think I just gave her the stink guy.
• 2:12
  Speaker 2: That's a very powerful nonverbal communication.
• 2:16
  Speaker 1: That's right, that's right.
• 2:17
  Speaker 2: But one thing that's wonderful about the night sky and
• 2:19
  Speaker 2: about the universe is that it does inspire the sort
• 2:22
  Speaker 2: of kiddo's sense of wonder in all of us looking
• 2:25
  Speaker 2: up at the stars and wondering what they are and
• 2:28
  Speaker 2: how they work. It's sort of like a common thread
• 2:31
  Speaker 2: through all of human existence, probably going back thousands of years.
• 2:34
  Speaker 1: It's true. Probably some of the most profound and the
• 2:37
  Speaker 1: most wish I was able to be profound statements have
• 2:42
  Speaker 1: been said while looking at the night sky.
• 2:46
  Speaker 2: And Welcome to the podcast Daniel and Jorge Explain the
• 2:49
  Speaker 2: Universe in which we try to be profound about the
• 2:52
  Speaker 2: nature of the universe. We stare out into the vast
• 2:55
  Speaker 2: cosmos and wonder how does it all work? What's going
• 2:58
  Speaker 2: on out there? Can we make makes sense of any
• 3:01
  Speaker 2: of it or all of it or none of it?
• 3:03
  Speaker 2: And so on this podcast we dig deep into the
• 3:05
  Speaker 2: mysteries of the universe and try to explain all of
• 3:07
  Speaker 2: them to you. My friend and regular co host Jorge
• 3:10
  Speaker 2: can't be here today, but I'm very happy to be
• 3:12
  Speaker 2: talking about the nature of the night sky with my
• 3:15
  Speaker 2: friend Kelly. Kelly, thanks very much for joining us.
• 3:17
  Speaker 1: Thanks, I'm happy to be here, and I'm keeping my
• 3:20
  Speaker 1: fingers crossed that we don't talk about anything that's going
• 3:22
  Speaker 1: to scare me or my kids today, So I guess
• 3:24
  Speaker 1: we'll see what happens.
• 3:27
  Speaker 2: We're going to talk about fun stuff today, but we're
• 3:29
  Speaker 2: also going to talk about big cataclysmic events. Oh uh oh, yeah, exactly,
• 3:37
  Speaker 2: and we are going to try to touch back on
• 3:39
  Speaker 2: that sense of all and wonder that we have when
• 3:43
  Speaker 2: we look up at the night sky. Because something that
• 3:45
  Speaker 2: I love when I see the night sky is thinking
• 3:48
  Speaker 2: about how other humans saw it, you know, cave people
• 3:52
  Speaker 2: or even proto humans looking up at the stars, wondering
• 3:55
  Speaker 2: what they were, not realizing how many secrets about the
• 3:59
  Speaker 2: nature of the universe they contained, the messages that are
• 4:02
  Speaker 2: coming to us from outer space telling us about how
• 4:05
  Speaker 2: the universe works.
• 4:06
  Speaker 1: Yeah, I wonder if it was mostly scary or mostly
• 4:09
  Speaker 1: like relaxing to look up at the night sky back
• 4:11
  Speaker 1: when we had no idea what it was.
• 4:13
  Speaker 2: Probably some combination of both. I had an amazing experience
• 4:16
  Speaker 2: a few years ago because I got to be in
• 4:18
  Speaker 2: the path of totality for the most recent eclipse that
• 4:21
  Speaker 2: went through North America. And I was excited about it
• 4:23
  Speaker 2: because you know, I'm a space nerd, but frankly, I
• 4:26
  Speaker 2: was preparing to be a little bit underwhelmed. Like you know,
• 4:29
  Speaker 2: fireworks and Fourth of July, for example, we've all seen
• 4:32
  Speaker 2: them before. It's exciting, I guess, but it doesn't really
• 4:34
  Speaker 2: blow your socks off. I was sort of expecting that
• 4:37
  Speaker 2: kind of experience, but I was totally surprised and amazed
• 4:41
  Speaker 2: at the depth of the experience, the like really shocking
• 4:45
  Speaker 2: overwhelming nature of that experience, And part of it was
• 4:47
  Speaker 2: thinking about what it must have been like for ancient
• 4:50
  Speaker 2: peoples to have something like really central in their existence,
• 4:54
  Speaker 2: the sun just like go away for a few minutes.
• 4:58
  Speaker 2: What must have that been like if you didn't have
• 5:00
  Speaker 2: any understanding about what was happening.
• 5:02
  Speaker 1: And I think it impacts more than just humans, Like
• 5:04
  Speaker 1: I've heard that in some of the areas when the
• 5:07
  Speaker 1: sun goes away in the middle of the day, insects
• 5:09
  Speaker 1: will start chirping like it's nighttime, like even their kind
• 5:13
  Speaker 1: of thrown like it's nighttime and the nighttime has gone
• 5:15
  Speaker 1: away again, and what is the world doing. I don't
• 5:18
  Speaker 1: know if they have a stress response, but it seems
• 5:20
  Speaker 1: to throw all of us off.
• 5:21
  Speaker 2: It is very strange, and it makes me very glad
• 5:23
  Speaker 2: that we have some understanding of why it happens, so
• 5:26
  Speaker 2: we don't all have to be terrified that like the
• 5:28
  Speaker 2: basic deal in which we live is suddenly changed for
• 5:32
  Speaker 2: reasons we don't understand. And I understand now, like why
• 5:35
  Speaker 2: the Chinese and the Babylonians and the Mayans were so
• 5:38
  Speaker 2: intent on understanding what was going on in the cosmos
• 5:42
  Speaker 2: and keeping track of it and trying to predict the
• 5:44
  Speaker 2: clipses and all this kind of stuff.
• 5:45
  Speaker 3: Yeah.
• 5:45
  Speaker 2: Absolutely, it's super fun actually to dig in the details
• 5:48
  Speaker 2: of like how the Greeks did astronomy and how the
• 5:50
  Speaker 2: Chinese did astronomy without understanding geometry and all this kind
• 5:54
  Speaker 2: of stuff. Super fascinating things we can dig into on
• 5:57
  Speaker 2: another episode, But today we want to go even further back.
• 6:00
  Speaker 2: Not just wondering if ancient Chinese and Babylonian astronomers were
• 6:04
  Speaker 2: looking at at the same night sky as we were
• 6:06
  Speaker 2: and having the same feelings of on wonder, We want
• 6:09
  Speaker 2: to go deep, deep into the real history of the
• 6:12
  Speaker 2: Earth and wonder like, what did the night sky look
• 6:14
  Speaker 2: like a million years ago, fifty million years ago? How
• 6:18
  Speaker 2: much does it change? After all?
• 6:20
  Speaker 1: That's so, how far back are we going?
• 6:23
  Speaker 2: So on today's episode we're going to ask the question
• 6:30
  Speaker 2: what did the night sky look like to the dinosaurs?
• 6:34
  Speaker 2: Whoa exactly if you were a dinosaur astronomer, I guess
• 6:39
  Speaker 2: that would be like a dino astronomer or an astronosaurus.
• 6:44
  Speaker 2: I'm not sure what you would call that. What would
• 6:49
  Speaker 2: you see if you looked up at the night sky.
• 6:51
  Speaker 2: Are we looking up at basically the same night sky
• 6:54
  Speaker 2: as a dinosaurs or did the dinosaurs live long enough
• 6:57
  Speaker 2: ago that enough cosmic time has elapsed that things could
• 7:01
  Speaker 2: actually look different.
• 7:02
  Speaker 1: Well, you asked a bunch of smart people this question.
• 7:04
  Speaker 1: Should we see what they had to say?
• 7:06
  Speaker 2: I did exactly that. Thank you very much to our
• 7:08
  Speaker 2: listeners who participate in this segment of the podcast, giving
• 7:12
  Speaker 2: us a sense for what people out there know and
• 7:14
  Speaker 2: do not know about the question of the day. So
• 7:17
  Speaker 2: thanks very much to everybody who participates. If you would
• 7:19
  Speaker 2: like to hear your voice speculating basisly on the podcast,
• 7:22
  Speaker 2: please write to me two questions at Danielandjorge dot com.
• 7:26
  Speaker 2: Everybody is welcome. So before you hear these listeners' answers,
• 7:29
  Speaker 2: think to yourself, do you think astronosauruses were studying the
• 7:33
  Speaker 2: same night sky as we were?
• 7:36
  Speaker 5: Well, that's an interesting question. I know that the constellations
• 7:40
  Speaker 5: that we see in the sky are not static. The
• 7:47
  Speaker 5: universe is moving, The galaxy is moving, our Solar system
• 7:51
  Speaker 5: is moving with respect to the other stars. It's just
• 7:55
  Speaker 5: it's happening on a very slow scale. So on the
• 7:59
  Speaker 5: scale of Dinas Stares sixty five million years ago. They
• 8:02
  Speaker 5: probably didn't see the same constellations that we see. Some
• 8:07
  Speaker 5: of the stars that we see today probably they saw
• 8:10
  Speaker 5: as well, but they probably saw other stars that are
• 8:12
  Speaker 5: no longer there.
• 8:15
  Speaker 6: I'm guessing that the night sky looked quite similar. However,
• 8:20
  Speaker 6: some stars were likely brider on account that the universe
• 8:23
  Speaker 6: hadn't expanded as much.
• 8:26
  Speaker 3: I don't think the sky looked really different for dinosaurs.
• 8:29
  Speaker 3: I mean, sixty five million years not a lot for
• 8:31
  Speaker 3: the universe, so I think the skyes looked pretty much
• 8:36
  Speaker 3: the same, maybe a little more stars here and there,
• 8:40
  Speaker 3: not so different.
• 8:41
  Speaker 7: I think in the time of the dinosaurs, this night
• 8:44
  Speaker 7: sky probably looked a bit more condensed with stars like
• 8:49
  Speaker 7: the constellations were maybe more close together, although there were
• 8:54
  Speaker 7: other stars that were visible that on anymore.
• 8:57
  Speaker 4: I can't imagine there'd be a lot of light pollution,
• 9:00
  Speaker 4: so you'd get to see a lot more stars, probably
• 9:02
  Speaker 4: different nebulas than we have now, different constellations, and I
• 9:07
  Speaker 4: can imagine there was an asteroid approaching at one point.
• 9:10
  Speaker 8: I think that the sky for dinos, the night sky
• 9:13
  Speaker 8: for Dino's would look like filled with more stars because
• 9:19
  Speaker 8: then there was no light pollution and distant galaxies were
• 9:24
  Speaker 8: slightly closer to worth some billion years ago.
• 9:28
  Speaker 1: So I was really surprised by how diverse the answers
• 9:32
  Speaker 1: were here. There's a lot of different you know, the
• 9:34
  Speaker 1: answers ranged from pretty much nothing has probably changed to
• 9:38
  Speaker 1: different stars. And I hadn't actually even considered that maybe
• 9:42
  Speaker 1: our conversation would include light pollution. So I thought that
• 9:45
  Speaker 1: was an interesting thing to include and a very good point.
• 9:48
  Speaker 1: But yeah, so they you know, they were thinking about
• 9:50
  Speaker 1: what are Cosmolalasaurus. There's got to be a way to
• 9:56
  Speaker 1: shorten it, but what they were looking at, So, can
• 10:00
  Speaker 1: can you give me a sense of like how long
• 10:02
  Speaker 1: ago we were talking here with the dinosaurs?
• 10:04
  Speaker 2: Yeah, so the dinosaurs are really deep in the past, right.
• 10:08
  Speaker 2: We're used to thinking about humans arising fifty one hundred
• 10:11
  Speaker 2: thousand years ago and the evolution of our ancestors over
• 10:14
  Speaker 2: the last few million years. But dinosaurs, we think were
• 10:17
  Speaker 2: wiped out about sixty five million years ago, and they
• 10:21
  Speaker 2: lasted for a long long time before that. We're talking
• 10:24
  Speaker 2: about like the Triassic Period started about two hundred and
• 10:27
  Speaker 2: fifty million years ago Jurassic, which is when we had
• 10:30
  Speaker 2: like stegosauruses like two hundred million years ago, and then
• 10:35
  Speaker 2: the Cretaceous period when we had like the t rex
• 10:37
  Speaker 2: and the triceratops, that's like one hundred and fifty million
• 10:40
  Speaker 2: years ago till about when that asteroid hit like sixty
• 10:43
  Speaker 2: five million years ago, So that's like really a long
• 10:46
  Speaker 2: time compared to human existence, though of course it's still
• 10:50
  Speaker 2: pretty short compared to like the age of the universe,
• 10:53
  Speaker 2: which is fourteen billion years, and even the age of
• 10:57
  Speaker 2: the Earth, which is four and a half billion years.
• 11:00
  Speaker 2: One of my favorite things about astronomy is just like
• 11:03
  Speaker 2: the length of these crazy timelines. You know, so much
• 11:07
  Speaker 2: happens on Earth in basically the blink of an eye
• 11:10
  Speaker 2: from the point of view of the cosmos.
• 11:11
  Speaker 1: And I am so bad thinking about like units and
• 11:14
  Speaker 1: how to compare them. Like, you know, my husband laughs
• 11:18
  Speaker 1: if we have to say, you know, oh, how much
• 11:19
  Speaker 1: is two inches, He'll be like, no, no, don't even ask Kelly,
• 11:22
  Speaker 1: because I'll be like us anywhere from you know, like
• 11:24
  Speaker 1: I don't know, my fingers are showing like a foot
• 11:26
  Speaker 1: to a centimeter, and I'm just like, I'm pretty bad
• 11:30
  Speaker 1: at this stuff. So my brain has a little trouble
• 11:33
  Speaker 1: wrapping itself around questions like this. So, so how do
• 11:37
  Speaker 1: we start thinking about this question.
• 11:39
  Speaker 2: Yeah, I think maybe we should start by thinking about
• 11:41
  Speaker 2: what we are seeing in the night sky, like what
• 11:44
  Speaker 2: is up there that we can see, and then we
• 11:46
  Speaker 2: can dig back into the past and think about how
• 11:49
  Speaker 2: things are changing, because you're right, the listeners give us
• 11:51
  Speaker 2: a lot of really cool clues, like thinking about light
• 11:54
  Speaker 2: pollutions and the expansion of the universe and the constellations,
• 11:59
  Speaker 2: and I think there's a lot of great stuff to
• 12:01
  Speaker 2: dig into. But maybe we should start with what we're
• 12:03
  Speaker 2: seeing in the night sky, like what is up there
• 12:06
  Speaker 2: in the night sky for us to see? When you
• 12:08
  Speaker 2: stand out there with your kids staring up the night sky,
• 12:10
  Speaker 2: sip in your hot coco, what is it exactly that
• 12:13
  Speaker 2: you're seeing? And I think people will be surprised to
• 12:16
  Speaker 2: learn what we're seeing and what we're not seeing. Like
• 12:19
  Speaker 2: if you ask people how many stars are visible in
• 12:22
  Speaker 2: the night sky, they typically come up with like really
• 12:24
  Speaker 2: big numbers, thousands and thousands, millions and millions of stars,
• 12:28
  Speaker 2: because they know that there are lots of stars out
• 12:30
  Speaker 2: there in the universe, but when you look up at
• 12:32
  Speaker 2: the night sky, they're only about a few thousand that
• 12:35
  Speaker 2: you can see with the naked eye.
• 12:38
  Speaker 1: WHOA. I would have guessed that number was much bigger,
• 12:41
  Speaker 1: and so is we talking like two thousand.
• 12:43
  Speaker 2: So there are nine thousand stars in the Milky Way
• 12:45
  Speaker 2: that are bright enough to see with the naked eye.
• 12:48
  Speaker 2: The brightest one is called Vega, but it's still pretty dim.
• 12:52
  Speaker 2: It's like one hundred and twenty five thousand times dimmer
• 12:56
  Speaker 2: than the full moon, and most of the stars that
• 12:59
  Speaker 2: are out there are like less than a percent as
• 13:02
  Speaker 2: bright as Vega. Now, I don't want to be dissing
• 13:04
  Speaker 2: these stars, right, Remember, these guys are really far away.
• 13:07
  Speaker 2: We're talking about light years or tens of light years
• 13:10
  Speaker 2: or thousands of light years away. So it's amazing that
• 13:13
  Speaker 2: you can see this ball of gas burning from light
• 13:16
  Speaker 2: years and light years away from billions and billions of
• 13:18
  Speaker 2: miles right, Like, that's just another sense of awe. I
• 13:21
  Speaker 2: remember teaching my kids that, like, the Sun is crazy
• 13:25
  Speaker 2: far away, like ridiculously far away, but it's so big
• 13:29
  Speaker 2: that you can still feel it through ninety million miles
• 13:32
  Speaker 2: of space.
• 13:33
  Speaker 3: Right.
• 13:33
  Speaker 2: Even just that fact still amazes me when I think
• 13:36
  Speaker 2: about it. So, these stars are out there, they're burning bright.
• 13:38
  Speaker 2: It's incredible that we can see them over such great distances,
• 13:43
  Speaker 2: But there really are only nine thousand that are capable
• 13:45
  Speaker 2: of being spotted on a given night, and so if
• 13:48
  Speaker 2: you're standing on the earth looking up, you're seeing some
• 13:50
  Speaker 2: fraction of those. So it's really just a few thousand stars.
• 13:53
  Speaker 1: To be honest, this is making me wish that we
• 13:55
  Speaker 1: had another kind of biologist expert on the show right now,
• 13:58
  Speaker 1: like someone who could tell us about eye vision. You know,
• 14:01
  Speaker 1: how many of those nine thousand stars that we can
• 14:04
  Speaker 1: see with our naked eyes do we think that maybe
• 14:07
  Speaker 1: the dinosaurs would have been able to see based on
• 14:09
  Speaker 1: like the size of their eye sockets and what we
• 14:12
  Speaker 1: know about vision and birds and reptiles or something now,
• 14:15
  Speaker 1: But we're gonna have to let that go for now.
• 14:16
  Speaker 2: I Yes, we'll ask Katie that question next time she's
• 14:19
  Speaker 2: on the podcast.
• 14:20
  Speaker 1: There you go.
• 14:21
  Speaker 2: Yes, dinosaurs with glasses, dinosaurs with like binoculars. You know,
• 14:26
  Speaker 2: there's a whole great comic vein to mine there, you know,
• 14:29
  Speaker 2: with t Rex even be able to put glasses on
• 14:31
  Speaker 2: because his arms are so short.
• 14:34
  Speaker 1: Maybe maybe that would favor the evolution of social behavior,
• 14:37
  Speaker 1: you know, so that you could have someone help you
• 14:38
  Speaker 1: put your glass floe or maybe.
• 14:40
  Speaker 2: The reason t Rex has never developed astronomy, was just
• 14:43
  Speaker 2: because they couldn't hold the telescope up to their eyes.
• 14:46
  Speaker 2: Otherwise it might have saved them, right if they had
• 14:48
  Speaker 2: developed astronomy and seen the asteroid coming, boy, life could have.
• 14:52
  Speaker 1: Been different, absolutely so. But we're lucky that they didn't.
• 14:56
  Speaker 2: We are we are all lucky. We have no complaints
• 14:59
  Speaker 2: about the history as it happened. But you know, we
• 15:01
  Speaker 2: know that there are other things up there in the
• 15:03
  Speaker 2: night sky as well, right like we know that the
• 15:05
  Speaker 2: galaxy is just one of many galaxies in the universe,
• 15:09
  Speaker 2: and we're used to talking about the other galaxies here
• 15:11
  Speaker 2: on the podcast and how the universe is expanding. We're
• 15:14
  Speaker 2: part of a cluster and a supercluster and et cetera.
• 15:16
  Speaker 2: But the interesting thing is that when you look up
• 15:17
  Speaker 2: at the night sky, you mostly can't see those other galaxies.
• 15:21
  Speaker 2: I mean, this is an incredible number of them, but
• 15:23
  Speaker 2: they're really, really, really far away. It takes special equipment
• 15:27
  Speaker 2: to see them. You might imagine, for example, the Hubble
• 15:30
  Speaker 2: deep field. That's this famous picture where the Hubble focused
• 15:33
  Speaker 2: on a single spot in the sky for a long time,
• 15:36
  Speaker 2: gathered all those fained photons and it came away with
• 15:39
  Speaker 2: this shocking image. Shocking because it's so chock full of galaxies.
• 15:43
  Speaker 2: It's just like grains of sand on the beach. You know,
• 15:45
  Speaker 2: there's just galaxies everywhere, but you can't see them mostly,
• 15:48
  Speaker 2: and you definitely can't see them with the naked eye
• 15:51
  Speaker 2: because so few photons arive from them that you need
• 15:55
  Speaker 2: like a really big aperture and a really long time
• 15:58
  Speaker 2: to even see a single photon from those distant galaxies.
• 16:01
  Speaker 1: And the dinosaurs definitely didn't have the web telescope.
• 16:04
  Speaker 2: So and there's something really interesting and sort of quantum
• 16:08
  Speaker 2: mechanical there that some listeners write in and ask me about.
• 16:11
  Speaker 2: They like to think about the photons flying away from
• 16:14
  Speaker 2: that galaxy. And you know, in principle they're flying in
• 16:16
  Speaker 2: every direction, but photons are discrete, right, They're little bundles,
• 16:20
  Speaker 2: and so they fly like in one direction and in
• 16:22
  Speaker 2: not another, which means if you're really close up to
• 16:25
  Speaker 2: the galaxy, you're getting lots of photons from it, But
• 16:28
  Speaker 2: as you get further and further away, there can start
• 16:30
  Speaker 2: to be gaps places where like no photon from that
• 16:34
  Speaker 2: galaxy is now arriving. You wait long enough, eventually you'll
• 16:38
  Speaker 2: get lucky and a photon will spray out in just
• 16:40
  Speaker 2: your direction to fly across the universe and hate your eyeball.
• 16:44
  Speaker 2: But you're not guaranteed. Right. There are moments where there
• 16:46
  Speaker 2: are zero photons arriving from a distant galaxy, and that's
• 16:49
  Speaker 2: why you just can't see them. You need to wait
• 16:52
  Speaker 2: long enough, or like point Hubble at it long enough
• 16:55
  Speaker 2: to sort of integrate enough photons. These things emerge from
• 16:59
  Speaker 2: the blacknest.
• 17:00
  Speaker 1: Like a cosmic invisibility sort of.
• 17:04
  Speaker 2: And even the nearby galaxies are not easy to spot,
• 17:07
  Speaker 2: like our neighbor Andromeda. It's a few million light years away,
• 17:10
  Speaker 2: but it's a huge monster galaxy. It's much bigger than
• 17:14
  Speaker 2: our galaxy. In fact, it's so big that if you
• 17:17
  Speaker 2: could see it, it would be larger in the sky
• 17:20
  Speaker 2: than the full moon. Whoa, yeah, but it's just not
• 17:24
  Speaker 2: that bright because it's so far away, so it's basically
• 17:27
  Speaker 2: invisible to the naked eye. But you know, you set
• 17:30
  Speaker 2: up a telescope and point it in the right spot
• 17:32
  Speaker 2: for long enough, you can get really amazing pictures of Andromeda.
• 17:36
  Speaker 2: And I feel like that would change our whole concept
• 17:39
  Speaker 2: of galaxies and what they are. If we could have
• 17:41
  Speaker 2: seen Andromeda imagine just like having another galaxy out there
• 17:45
  Speaker 2: for us to look at from the outside would have
• 17:49
  Speaker 2: given us such a huge clue about like what was
• 17:51
  Speaker 2: going on out there in the universe.
• 17:53
  Speaker 1: I can also imagine that, yeah, being very scary if
• 17:56
  Speaker 1: you didn't know what it was.
• 17:57
  Speaker 2: That's true. And you know, it was only like a
• 18:00
  Speaker 2: one hundred years ago that Hubble realized that there are
• 18:03
  Speaker 2: other galaxies out there. Until then, we thought our galaxy
• 18:06
  Speaker 2: was the only one just floating out there in space.
• 18:09
  Speaker 2: And it's when Hubble realized that those little smudges that
• 18:12
  Speaker 2: were just barely visible in his telescopes were actually super
• 18:15
  Speaker 2: duper far away. He and some other astronomers developed a
• 18:18
  Speaker 2: way to measure the distance to them. That's when he realized, oh,
• 18:22
  Speaker 2: those little smudges are actually entire other galaxies, super far away.
• 18:26
  Speaker 2: That's how hard they are to see and to study,
• 18:28
  Speaker 2: and how recently we've understood that they're even there. So
• 18:32
  Speaker 2: our ancestors, Chinese astronomers, Babylonian astronomers had no idea that
• 18:37
  Speaker 2: there were other galaxies up there in the night sky.
• 18:39
  Speaker 1: And this is why it's great that we fund science
• 18:41
  Speaker 1: more now. So that's what things look like now. Let's
• 18:46
  Speaker 1: take a break, and when we get back, let's talk
• 18:48
  Speaker 1: about how that view changes over time. Okay, so we
• 19:03
  Speaker 1: talked about how we can see about nine thousand stars
• 19:06
  Speaker 1: in the sky with our naked eye, and some of
• 19:09
  Speaker 1: them are pretty dim and stuff that's far away is
• 19:11
  Speaker 1: too faint to see, including galaxies. How did that view
• 19:14
  Speaker 1: change over time?
• 19:15
  Speaker 2: So there's a lot of really interesting aspects here. You know,
• 19:18
  Speaker 2: there is a questioning of light pollution. There's the question
• 19:21
  Speaker 2: of the moon. There's how the constellations might change. There's
• 19:24
  Speaker 2: how the galaxy rotates. There's the expansion of the universe.
• 19:28
  Speaker 2: There's asteroids, you know, coming to hit the Earth that
• 19:31
  Speaker 2: we or dinosaurs might have spotted. So let's take them
• 19:35
  Speaker 2: one at a time and dig into each one and
• 19:36
  Speaker 2: think about how it impacts our view of the night
• 19:39
  Speaker 2: sky and the dinosaur's view of the night sky. The
• 19:41
  Speaker 2: first one, because I love this response from the listeners, is,
• 19:44
  Speaker 2: of course light pollution right now. Clearly, if you're living
• 19:47
  Speaker 2: in New York City or a big city and you
• 19:49
  Speaker 2: look by the night sky, you're not seeing a whole
• 19:51
  Speaker 2: lot of stars. Maybe you saw the recent conjunction of
• 19:54
  Speaker 2: Jupiter and Venus. Maybe you see the North Star. But
• 19:57
  Speaker 2: you know, just most of the stars out there are
• 20:00
  Speaker 2: sort of overshadowed by the light from your city. And
• 20:03
  Speaker 2: this happens during the day too, right, you look up
• 20:05
  Speaker 2: at the sky during the day. The stars are there,
• 20:07
  Speaker 2: they're sending photons at you. It's just that you can't
• 20:10
  Speaker 2: see them because they're not overshadowed. It's the word over
• 20:13
  Speaker 2: photon or out shown. There you go, they're out shown
• 20:16
  Speaker 2: by the sun. They go, You're blinded by the light
• 20:19
  Speaker 2: of the sign and so you just can't see them.
• 20:21
  Speaker 2: And you know, we imagine dinosaurs, of course, did not
• 20:24
  Speaker 2: build large metropolises, you know, or metropolisauruses, and so they
• 20:29
  Speaker 2: didn't have light pollution. Unless you're a believer in like
• 20:32
  Speaker 2: you know, atlantis or like ancient aliens or some other
• 20:35
  Speaker 2: kind of nonsense.
• 20:37
  Speaker 1: That's for a different show, a different show.
• 20:40
  Speaker 2: That's for a different show where it's sticking to the
• 20:41
  Speaker 2: actual science here. Then probably the dinosaurs didn't have to
• 20:44
  Speaker 2: contend with light pollution, and so they could see the
• 20:47
  Speaker 2: night sky as well as we can under the best circumstances.
• 20:51
  Speaker 2: And while if you live in a city, you're not
• 20:53
  Speaker 2: seeing it under the best circumstances. There's still a lot
• 20:56
  Speaker 2: of places in the country and in the world you
• 20:58
  Speaker 2: can go to get a pretty good dark sky. It's
• 21:01
  Speaker 2: unfortunately getting smaller and smaller as humans encroach on every
• 21:04
  Speaker 2: last piece of the planet, but it is still possible,
• 21:07
  Speaker 2: and if you go camping you can get a pretty
• 21:09
  Speaker 2: good dark sky experience.
• 21:11
  Speaker 1: I consider this one of the biggest perks of living
• 21:13
  Speaker 1: out in the middle of nowhere is the uh, the
• 21:16
  Speaker 1: lower light pollution.
• 21:17
  Speaker 2: Yeah, and if you're not somebody who regularly sees that
• 21:21
  Speaker 2: kind of sky, it can be kind of alarming or
• 21:23
  Speaker 2: shocking or just you know, awe inspiring. If you do
• 21:26
  Speaker 2: go out camping and you look up, you're like, wow,
• 21:28
  Speaker 2: all these stars are here, like all the time. It's
• 21:32
  Speaker 2: an incredible view, and I think most people underappreciate it.
• 21:35
  Speaker 2: You know, you stand on like the top floor the
• 21:38
  Speaker 2: Empire State Building, You're like, Wow, what a view I
• 21:40
  Speaker 2: can see for miles right. Well, if you look up
• 21:43
  Speaker 2: in the night sky, you're seeing for billions of miles, Like,
• 21:47
  Speaker 2: what a view that is. You know, it's incredible and
• 21:50
  Speaker 2: we're so lucky that it even exists, that everything is
• 21:53
  Speaker 2: set up in the universe for there to be stars
• 21:55
  Speaker 2: that shines photons and for it to be mostly transparent
• 21:57
  Speaker 2: so that light can get to us. I'm like totally
• 22:00
  Speaker 2: proselytizing for astronomy here, but I just feel like people
• 22:02
  Speaker 2: don't experience and appreciate that enough.
• 22:04
  Speaker 1: I think it's one of the greatest experiences in life
• 22:07
  Speaker 1: when you get a really good clear night sky. I
• 22:09
  Speaker 1: was in Costa Rica once and I could see it
• 22:11
  Speaker 1: was the clearest I've ever seen the night sky. And
• 22:13
  Speaker 1: it was my job to tend the turtles that were hatching,
• 22:17
  Speaker 1: and so I would like see shooting stars and then
• 22:22
  Speaker 1: help some turtles get to the ocean. And it was
• 22:24
  Speaker 1: like the greatest mix of space and biology, like like
• 22:28
  Speaker 1: my two loves coming together at once, and it was
• 22:31
  Speaker 1: the happiest I think I've ever been anyway.
• 22:34
  Speaker 2: Well, something that could really impact your ability to see
• 22:37
  Speaker 2: the stars in the sky is the moon. You want
• 22:39
  Speaker 2: to have like a really good dark night experience, you
• 22:42
  Speaker 2: need a new moon because the moon is crazy bright.
• 22:45
  Speaker 2: As we said, it's like thousands and thousands of times
• 22:47
  Speaker 2: brighter than even the brightest star in the sky, so
• 22:51
  Speaker 2: it can really spoil in her dark night. But it's
• 22:54
  Speaker 2: also interesting to think about, like what the moon looked
• 22:56
  Speaker 2: like to dinosaurs. Because while we think about maybe things
• 22:59
  Speaker 2: out in deep space, other galaxies, whatever, changing over time,
• 23:03
  Speaker 2: the Moon is also not static, like it's been orbiting
• 23:06
  Speaker 2: the Earth for lots and lots of years, but its
• 23:09
  Speaker 2: orbit is actually changing every year by how much? So
• 23:12
  Speaker 2: the Moon is orbiting the Earth and its orbit gets
• 23:15
  Speaker 2: larger by a couple of centimeters every year. Now, I know, Kelly,
• 23:18
  Speaker 2: you're not good with units, but like if you open
• 23:20
  Speaker 2: your fingers, you know.
• 23:22
  Speaker 1: Uh huh, all right, I'm doing it.
• 23:23
  Speaker 2: It's like the height of a really thick pastrami sandwich
• 23:26
  Speaker 2: or something, you know, so like a foot Wow, I
• 23:30
  Speaker 2: want to eat a Stromi sandwich at your house sometimes.
• 23:33
  Speaker 1: Yeah, Yeahoatmith house, I believe it.
• 23:36
  Speaker 2: And some of Zach's homemade rye bred of it. So
• 23:38
  Speaker 2: you might imagine that like two and a half centimeters
• 23:40
  Speaker 2: a year doesn't sound like a lot, but we got
• 23:43
  Speaker 2: a lot of years here, right, Like the diners were
• 23:45
  Speaker 2: lived a long time ago, and one hundred million years
• 23:48
  Speaker 2: adds up to like two thousand, two hundred kilometers over
• 23:53
  Speaker 2: all that time. So the Moon is further away from
• 23:57
  Speaker 2: the Earth by twenty two hundred kilometers than it was
• 24:00
  Speaker 2: when the dinosaurs were looking up at it.
• 24:02
  Speaker 1: Oh my gosh, So what is the total distance? Like,
• 24:04
  Speaker 1: what is the percent difference?
• 24:06
  Speaker 2: Yeah, that's exactly the right question, right, it doesn't make
• 24:08
  Speaker 2: any difference at all. Because if your friend was right
• 24:11
  Speaker 2: next to you and then a moment later they're twenty
• 24:13
  Speaker 2: two hundred cilometers away, it's going to make a big difference.
• 24:16
  Speaker 2: But the moon is not right next to us, and
• 24:18
  Speaker 2: was never right next to us on these time scales.
• 24:21
  Speaker 2: Its current distance is like three hundred and eighty three
• 24:24
  Speaker 2: thousand kilometers, so we're talking about like two thousand kilometers
• 24:29
  Speaker 2: more than the dinosaurs used to see it. That's only
• 24:31
  Speaker 2: like a half a percent.
• 24:33
  Speaker 1: Difference, okay, And so like if I went back in
• 24:36
  Speaker 1: a time machine, I probably wouldn't be able to tell
• 24:39
  Speaker 1: the difference.
• 24:39
  Speaker 2: That's a great way to think about it. Like, if
• 24:40
  Speaker 2: you get a time machine, if somebody spins the dial
• 24:42
  Speaker 2: and sends you back to an arbitrary time, could you
• 24:45
  Speaker 2: use the night sky to figure out like when it was,
• 24:47
  Speaker 2: would you notice any difference? So if you went back
• 24:49
  Speaker 2: to like the Cretaceous period sometime in the middle of that,
• 24:53
  Speaker 2: then you look at the night sky, you would notice
• 24:55
  Speaker 2: the moon would be like one percent bigger and like
• 24:58
  Speaker 2: one percent brighter than it is today. And so unless
• 25:01
  Speaker 2: you're like extraordinarily sensitive to moonlight, you're like a werewolf
• 25:05
  Speaker 2: or something, then you probably wouldn't notice. But be careful
• 25:08
  Speaker 2: about sending your werewolves back in time.
• 25:10
  Speaker 1: Yeah, no, no, you shouldn't know. I'll be very careful.
• 25:13
  Speaker 2: And fiction writers out there, if you have time traveling werewolves,
• 25:16
  Speaker 2: I want you to include this detail. I mean we're
• 25:18
  Speaker 2: talking hard science fiction here, hard to read. Kelly. Somebody
• 25:26
  Speaker 2: out there is pouring their heart into a time traveling
• 25:29
  Speaker 2: werewolf novel and you just dissed it without even reading it.
• 25:32
  Speaker 1: I'm so sorry. I promise I'll have an open mind.
• 25:36
  Speaker 1: It might end up being great.
• 25:37
  Speaker 2: Please send us your fiction about time traveling werewolves. I
• 25:40
  Speaker 2: promise to read it with an open mind under a
• 25:42
  Speaker 2: very bright full moon.
• 25:44
  Speaker 1: That's right, that's right. Okay, I think we've said everything
• 25:48
  Speaker 1: that needs to be said about the moon, and then
• 25:50
  Speaker 1: maybe a lot more. How about constellations? Are they gonna
• 25:53
  Speaker 1: be the same? Is Orion's belt still going to be
• 25:56
  Speaker 1: there for our Cosmololosaurus to find?
• 25:59
  Speaker 2: So this is where a big change really happens. And
• 26:01
  Speaker 2: the short version is that the night sky could look
• 26:04
  Speaker 2: dramatically different to the dinosaurs than to us for a
• 26:08
  Speaker 2: few reasons. Number one is that stars are not infinitely old,
• 26:12
  Speaker 2: and they don't last for an infinite number of years. Remember,
• 26:15
  Speaker 2: stars form when you have like a big cloud of
• 26:17
  Speaker 2: gas and dust that's cold enough that gravity can like
• 26:21
  Speaker 2: pull on it. For gas that's too hot, the particles
• 26:23
  Speaker 2: are just moving too fast for gravity to like gather
• 26:26
  Speaker 2: it together into a star, and this can take a
• 26:29
  Speaker 2: long time. Remember, our star was only born four and
• 26:32
  Speaker 2: a half billion years ago, which means there were ten
• 26:34
  Speaker 2: billion years in the life of the universe, in like
• 26:36
  Speaker 2: nine billion years in the life of our galaxy before
• 26:39
  Speaker 2: our star even existed. Right, So stars are being born
• 26:43
  Speaker 2: all the time, and so some stars that we see
• 26:46
  Speaker 2: in the night sky didn't even exist when Tyrannosaurus Rex
• 26:51
  Speaker 2: was trying to invent a telescope that he could lift
• 26:53
  Speaker 2: to his eyeballs.
• 26:54
  Speaker 1: Wow, and we can age stars, so we can get
• 26:57
  Speaker 1: an estimate for how many didn't exist, Is that right?
• 26:59
  Speaker 2: Yeah, we can have an idea for how old stars
• 27:03
  Speaker 2: are because we have a model of star formation and
• 27:06
  Speaker 2: how stars burn, and as stars burn, they tend to
• 27:09
  Speaker 2: get like bigger and brighter, or there's some variation depending
• 27:13
  Speaker 2: on the initial clump of stuff they had. But there's
• 27:15
  Speaker 2: a whole deep knowledge now of like the life cycle
• 27:17
  Speaker 2: of stars, and so you can look at stars, and
• 27:20
  Speaker 2: you can look at stars nearby and understand how they
• 27:23
  Speaker 2: form together. We have a whole episode about how to
• 27:25
  Speaker 2: tell the age of stars. It's really a fascinating science.
• 27:28
  Speaker 2: Mostly you have to look at stars nearby and understand
• 27:31
  Speaker 2: how they all form together. But sometimes you can get
• 27:33
  Speaker 2: clues from an individual star. But you know, to take
• 27:36
  Speaker 2: a particular example, the Pliades, which are a famous constellation.
• 27:40
  Speaker 2: They're only like thirteen million years old, and so we're
• 27:44
  Speaker 2: looking up at the night sky, we're seeing that constellation.
• 27:47
  Speaker 2: It appears in like you know, ancient astronomical texts. People
• 27:51
  Speaker 2: have seen these. You can even find like neolithic records
• 27:55
  Speaker 2: of this constellation from like Bronze Age shields where they
• 27:59
  Speaker 2: have like hammered the night sky in a pattern onto
• 28:02
  Speaker 2: the shield and you can see the Pliades on it.
• 28:04
  Speaker 2: It's pretty awesome. So humans have always seen this constellation,
• 28:08
  Speaker 2: but dinosaurs never did. It just hadn't come out yet.
• 28:11
  Speaker 3: You know.
• 28:11
  Speaker 2: It's sort of like asking if dinosaurs have seen the
• 28:13
  Speaker 2: Star Wars movies.
• 28:15
  Speaker 1: You know, yet one more reason why it's good to
• 28:18
  Speaker 1: not be a dinosaur.
• 28:20
  Speaker 2: Although Star Wars happened a long long time ago, so
• 28:23
  Speaker 2: it might have been like actually occurring while the dinosaurs
• 28:25
  Speaker 2: were here. It just took a long time for the
• 28:27
  Speaker 2: movies to get here from that galaxy far far away.
• 28:33
  Speaker 1: An excellent point.
• 28:35
  Speaker 2: And you know, stars also die. We see supernova, which
• 28:38
  Speaker 2: are the endpoint of stars, stars that have burned for
• 28:40
  Speaker 2: so long that they've basically turned all of their fuel
• 28:43
  Speaker 2: into ash. You know, like our star can burn hydrogen
• 28:47
  Speaker 2: and it creates helium, but it can't burn that helium,
• 28:50
  Speaker 2: so the helium falls to the center of the star
• 28:52
  Speaker 2: and basically tries to put the star out. So that's
• 28:55
  Speaker 2: why our star then starts to burn on the outer
• 28:57
  Speaker 2: layers where there's still hydrogen, and it puffs up and
• 29:00
  Speaker 2: gets big. And all stars will do this, and eventually
• 29:02
  Speaker 2: they'll burn through all of the gas that they can burn,
• 29:05
  Speaker 2: and there be so much gravity that they collapse in
• 29:08
  Speaker 2: a huge gravitational implosion, which then bounces back into an explosion,
• 29:12
  Speaker 2: and you get these really dramatic events in the sky.
• 29:15
  Speaker 2: We call them supernova. And what's left is not a star.
• 29:18
  Speaker 2: We can actually look back in history and see records
• 29:20
  Speaker 2: of these things dating back to like a thousand years ago.
• 29:24
  Speaker 2: There was a huge supernova in ten fifty four that
• 29:28
  Speaker 2: the Chinese recorded, and like, this must have been a
• 29:31
  Speaker 2: very dramatic event. It lasted for a few months in
• 29:34
  Speaker 2: their sky, this sudden appearance of something very very bright.
• 29:38
  Speaker 2: They noted it as a guest star. And when we
• 29:41
  Speaker 2: look up at the night sky in the same spot,
• 29:42
  Speaker 2: we see a nebula, which is a huge spray of
• 29:45
  Speaker 2: material that erupted from that supernova. So that's pretty awesome. Actually,
• 29:49
  Speaker 2: because we have like a thousand years of observations of
• 29:53
  Speaker 2: this thing, we can see it exploding sort of over time.
• 29:56
  Speaker 2: But you know, the star that was there is now gone,
• 29:59
  Speaker 2: and so if you look back million years ago, you
• 30:01
  Speaker 2: would have seen that star, and today that star is
• 30:03
  Speaker 2: no longer there. So the night sky is definitely changing
• 30:07
  Speaker 2: on the thousand or million year timeline.
• 30:09
  Speaker 1: Okay, so the dinosaurs both saw stars that we never
• 30:15
  Speaker 1: got to see and don't even know existed because supernovas
• 30:18
  Speaker 1: don't leave signatures for quite for millions of years, and
• 30:22
  Speaker 1: we see some stars that they don't see, So do
• 30:24
  Speaker 1: we have a general like, is it like about ten
• 30:26
  Speaker 1: percent of the visible stars different now or is it
• 30:29
  Speaker 1: just no impossible to get a number like that.
• 30:32
  Speaker 2: That's a great question. I don't have a number, but
• 30:34
  Speaker 2: we do have a sort of a sense of it
• 30:36
  Speaker 2: by thinking about the kind of stars that are out
• 30:38
  Speaker 2: there in the universe. Like in our galaxy, most of
• 30:41
  Speaker 2: the stars are red dwarfs. These are smaller, cooler stars
• 30:45
  Speaker 2: than ours, and they also last a lot longer. Our
• 30:48
  Speaker 2: star will burn for ten billion years, these red dwarves
• 30:51
  Speaker 2: will burn for much much longer, sometimes one hundred billion
• 30:54
  Speaker 2: years for example. So we think the red dwarfs that
• 30:56
  Speaker 2: are out there that we're seeing will last a long time,
• 30:59
  Speaker 2: and any red dwarfs that exists at the time of
• 31:00
  Speaker 2: the dinosaurs probably also exist. But the flip side of
• 31:04
  Speaker 2: that is when you look for the night sky, you
• 31:05
  Speaker 2: don't see any red dwarfs because even though they're the
• 31:09
  Speaker 2: most common star in the galaxy, they're so dim that
• 31:12
  Speaker 2: you really can't see any of them with the naked eye.
• 31:14
  Speaker 2: So that means that the stars we're seeing are the
• 31:16
  Speaker 2: brightest stars, which are the ones that are shortest lived,
• 31:20
  Speaker 2: and so like the typical life cycle of these stars
• 31:22
  Speaker 2: is much much shorter, though we're still talking typically hundreds
• 31:26
  Speaker 2: of millions of years or billions of years. And so
• 31:29
  Speaker 2: you know, of the nine thousand stars that we can see,
• 31:32
  Speaker 2: I'd be surprised if it was more than ten percent
• 31:34
  Speaker 2: that had burned out or been born in the time
• 31:37
  Speaker 2: since the dinosaurs.
• 31:38
  Speaker 1: Okay, so now we have a good sense for how
• 31:40
  Speaker 1: many of the stars both the dinosaurs and us got
• 31:43
  Speaker 1: to see, and when we get back from a break,
• 31:46
  Speaker 1: we'll talk about whether or not they're in the same spots.
• 32:01
  Speaker 1: All right, So you told us that the dinosaurs saw
• 32:05
  Speaker 1: some stars that we didn't get to see, and that
• 32:08
  Speaker 1: we see some stars that the dinosaurs didn't get to see.
• 32:11
  Speaker 1: Are the stars that sort of overlap in that ven diagram?
• 32:14
  Speaker 1: Are they in the same spots?
• 32:16
  Speaker 2: So the short answer is that they're not. Right. Stars
• 32:19
  Speaker 2: in the galaxy are not static. It's not like they're
• 32:22
  Speaker 2: all in the same place. Remember that the galaxy is rotating,
• 32:26
  Speaker 2: and that stars are moving through the galaxy, but not
• 32:29
  Speaker 2: all together. It's not like we're all in a merry
• 32:31
  Speaker 2: go round and everybody's picked their horse and they're going
• 32:34
  Speaker 2: up and down and they're just in the same place.
• 32:36
  Speaker 2: It's more like a crazy traffic circle in Europe where
• 32:39
  Speaker 2: everybody's driving at different speed, and some stars are like
• 32:42
  Speaker 2: weaving through other stars, and some stars are going in
• 32:44
  Speaker 2: the wrong direction, and so it's a lot more chaotic
• 32:47
  Speaker 2: than you might imagine. And over the timescale of like
• 32:50
  Speaker 2: hundreds of millions of years, a lot of these stars
• 32:53
  Speaker 2: move relative to Earth, and so we will not see
• 32:56
  Speaker 2: the same picture of the sky.
• 32:57
  Speaker 5: All right.
• 32:57
  Speaker 1: So, first of all, that sounds awful, not like those
• 33:00
  Speaker 1: traffic circles. One bit. It sounds very chaotic, and they're
• 33:03
  Speaker 1: probably running into each other. And it's amazing that we
• 33:05
  Speaker 1: can plot the paths of any of these. So how
• 33:07
  Speaker 1: much have things moved since the dinosaurs were around?
• 33:10
  Speaker 2: Yeah, maybe instead of traffic circle, we should say like
• 33:12
  Speaker 2: mumper cars. It's really much more dramatic than a typical
• 33:15
  Speaker 2: traffic circle where we hope nobody is colliding with each other. Well,
• 33:18
  Speaker 2: there's a big variation in the speeds of these stars.
• 33:21
  Speaker 2: The typical speed of stars relative to the Earth, it
• 33:24
  Speaker 2: can be like ten or twenty kilometers per second, but
• 33:28
  Speaker 2: some of them are super duper fast. There's some stars
• 33:31
  Speaker 2: they call like hypervelocity stars that can move up to
• 33:34
  Speaker 2: like one hundred kilometers per second, faster than like the
• 33:37
  Speaker 2: typical speed in the Milky Way. These are stars that
• 33:40
  Speaker 2: have like had some gravitational event happened to them. Maybe
• 33:44
  Speaker 2: they whizzed through the center of the galaxy and got
• 33:46
  Speaker 2: accelerated by the black hole or had some near approach
• 33:49
  Speaker 2: to something else which really changed their direction, and so
• 33:53
  Speaker 2: like a hypervelocity star would like move across the sky
• 33:56
  Speaker 2: very quickly on the timescale of us in the dinosaur.
• 34:00
  Speaker 2: But in general, things tend to move sort of in blobs.
• 34:02
  Speaker 2: Like stars are born not individually. Stars tend to be
• 34:06
  Speaker 2: born together. You have like a star forming region. We
• 34:09
  Speaker 2: call these stellar nurseries where a bunch of stars were
• 34:12
  Speaker 2: all made at once. We painted this picture of stars
• 34:15
  Speaker 2: forming from gas clouds collapsing. But it's not like one
• 34:18
  Speaker 2: gas cloud equals one star or one solar system. You
• 34:21
  Speaker 2: tend to have like a huge gas cloud and it
• 34:24
  Speaker 2: collapses into multiple stars all at once. So you have
• 34:28
  Speaker 2: a bunch of stars with like a common origin, and
• 34:31
  Speaker 2: then they tend to have like common kinematics. Right, they
• 34:34
  Speaker 2: move sort of as a group for a little while
• 34:37
  Speaker 2: until they dissipate and get absorbed into the general flow
• 34:40
  Speaker 2: of the milky Way. So instead of thinking of the
• 34:42
  Speaker 2: Milky Way as like a merry go round, think of
• 34:44
  Speaker 2: it like a bunch of different gangs on the bumper
• 34:47
  Speaker 2: car floor, like all moving together, competing with each other.
• 34:51
  Speaker 1: So this might be a silly question. Are constellations usually
• 34:55
  Speaker 1: from the same nursery or are constellations made up of
• 34:59
  Speaker 1: stars that are much farther apart than that, but our
• 35:01
  Speaker 1: brain just makes patterns with them anyway, Oh, it's.
• 35:03
  Speaker 2: A great question. The short answer is that you're not
• 35:06
  Speaker 2: guaranteed at all that constellations in the sky have stars
• 35:09
  Speaker 2: that are near each other, right, They just happen to
• 35:11
  Speaker 2: line up from our perspective, and so they might not
• 35:15
  Speaker 2: be near each other at all. There could be one
• 35:17
  Speaker 2: that's fairly dim but close to us, and we can
• 35:19
  Speaker 2: see it in another one that's super bright but far away,
• 35:22
  Speaker 2: and so it lines up in the sky near us.
• 35:24
  Speaker 2: And I always felt like constellations, I don't understand why
• 35:28
  Speaker 2: they're typically taught in the beginning of like astronomy courses,
• 35:31
  Speaker 2: because there's nothing to them, right. It's like casting a
• 35:34
  Speaker 2: bunch of dye on the floor and saying, like, let's
• 35:37
  Speaker 2: learn about the universe. From these random numbers that really
• 35:40
  Speaker 2: tells you nothing about what's happening in the universe. I mean,
• 35:42
  Speaker 2: I guess it's like accessible and that's how people like
• 35:45
  Speaker 2: latch onto astronomy by looking at the stars. But I
• 35:48
  Speaker 2: feel like there's so much actual science you can teach
• 35:50
  Speaker 2: people instead of like basically astrology. But some of the
• 35:53
  Speaker 2: constellations are moving together, like the Big Dipper, the Big Dipper,
• 35:57
  Speaker 2: most of those stars were formed about the same time,
• 36:00
  Speaker 2: and they're in a group that are all moving together.
• 36:03
  Speaker 2: And it's actually a very big, very fast moving group
• 36:06
  Speaker 2: of stars that are all sort of like running together
• 36:09
  Speaker 2: across the universe.
• 36:10
  Speaker 1: Are they all moving at hypervelocity.
• 36:13
  Speaker 2: Not quite at hypervelocity, but definitely tens of kilometers. And
• 36:17
  Speaker 2: it's one of the largest and closest of these kinematic groups.
• 36:20
  Speaker 2: They call it the ursa major moving group, so it
• 36:22
  Speaker 2: includes the Big Dipper, and it's moving so fast that
• 36:25
  Speaker 2: if you rewound the clocklin even just one hundred and
• 36:28
  Speaker 2: fifty thousand years, you would not see the Big Dipper
• 36:31
  Speaker 2: in the sky.
• 36:32
  Speaker 3: No.
• 36:33
  Speaker 2: Yeah, it's a good thing to check for when you
• 36:34
  Speaker 2: get out of your time machine with your werewolves. Yeah,
• 36:39
  Speaker 2: or fine, if you don't like traveling with a werewolfs
• 36:41
  Speaker 2: leave it at home, but still look up at the
• 36:43
  Speaker 2: night sky and check for the Big Dipper when you
• 36:45
  Speaker 2: get out of your time machine.
• 36:46
  Speaker 1: I feel like this is almost like rattling to me.
• 36:49
  Speaker 1: You know, one of the first things I learned about
• 36:51
  Speaker 1: the night sky was the Big Dipper, just like the
• 36:53
  Speaker 1: idea that it wasn't there for the dinosaurs is it
• 36:57
  Speaker 1: makes sense, but I guess I'd never thought of that.
• 36:59
  Speaker 2: That's OK, yeah, and it means that they definitely saw
• 37:02
  Speaker 2: other constellations. Like you would not recognize the night sky
• 37:06
  Speaker 2: from the dinosaurs times because it's dynamic. We tend to
• 37:09
  Speaker 2: think of it as static. And I look up in
• 37:10
  Speaker 2: the night sky and I wonder if you know ancient
• 37:12
  Speaker 2: astronomers or chro magnet man looked up the night sky
• 37:15
  Speaker 2: and saw the same thing. And most likely they did.
• 37:18
  Speaker 2: But you go far enough back in time, in deep
• 37:21
  Speaker 2: cosmic time, then you'll notice that these things are swimming.
• 37:24
  Speaker 2: I would love to see like a time lapse of
• 37:26
  Speaker 2: the sky dating back like one hundred and fifty million years,
• 37:30
  Speaker 2: because you would see things move right, and they are moving,
• 37:33
  Speaker 2: it's just moving so slowly that from our perspective, it
• 37:36
  Speaker 2: looks like nothing's happening. It's like checking in on the
• 37:38
  Speaker 2: Grand Canyon every couple of years being like, oh, this
• 37:41
  Speaker 2: thing's not changing, whereas we know right that over time,
• 37:44
  Speaker 2: of course, it's changing and growing, and a time lapse
• 37:47
  Speaker 2: would reveal it to be a dynamical system in progress.
• 37:51
  Speaker 2: Same thing with the stars. They're up there swirling around
• 37:53
  Speaker 2: and changing and swinging around each other, and the night
• 37:56
  Speaker 2: sky is definitely in motion.
• 37:58
  Speaker 1: It would be so cool to see that timeline. That's
• 38:01
  Speaker 1: never going to happen unless you get both the werewolf
• 38:04
  Speaker 1: at a time machine.
• 38:05
  Speaker 2: Or and there are other effects going on. It's not
• 38:09
  Speaker 2: just the night sky is changing around us that these
• 38:11
  Speaker 2: stars are moving relative to us. We're also moving relative
• 38:16
  Speaker 2: to the galaxy.
• 38:17
  Speaker 1: We're not in the center.
• 38:18
  Speaker 2: We're not in the center of the galaxy for sure.
• 38:20
  Speaker 2: Right we're like halfway out from the center. And you
• 38:23
  Speaker 2: should be glad we're not out in the center, because
• 38:25
  Speaker 2: it's crazy in there. You know, it's like very dense
• 38:28
  Speaker 2: with stars and radiation, and our kind of life could
• 38:30
  Speaker 2: not survive. We're safe out in the suburbs of the galaxy,
• 38:33
  Speaker 2: not so far out in like the exurbs with the
• 38:35
  Speaker 2: star density is very very low. We're like, you know,
• 38:37
  Speaker 2: halfway out from the center of the galaxy. But we
• 38:40
  Speaker 2: go around the galaxy and it takes like two hundred
• 38:42
  Speaker 2: and fifty million years for the galaxy to rotate. But
• 38:45
  Speaker 2: while that's happening, the Sun does this really interesting and
• 38:49
  Speaker 2: weird thing is that it goes up and down. So
• 38:52
  Speaker 2: imagine like the plane of the galaxy, the Milky Way
• 38:54
  Speaker 2: is like flat disk. The Sun is going through that
• 38:57
  Speaker 2: disk and then back out the bottom and then coming
• 38:59
  Speaker 2: back up again and through the top of it. It's
• 39:01
  Speaker 2: going like up and down in a sort of a
• 39:03
  Speaker 2: cyan wave through the disk of the galaxy.
• 39:06
  Speaker 1: The solar like the galaxies are dancing. Why does it
• 39:10
  Speaker 1: do that.
• 39:10
  Speaker 2: It's sort of like on the Merry Go Round where
• 39:12
  Speaker 2: your horse goes up and down and it's just oscillating.
• 39:15
  Speaker 2: Like most of the gravity is at the center of
• 39:17
  Speaker 2: the galaxy. And from this perspective, we mean like the
• 39:20
  Speaker 2: plane of the galaxy, and so it's attracted to the
• 39:24
  Speaker 2: plane of the galaxy, which slurps it in it applies
• 39:26
  Speaker 2: basically a force to it. But then when it gets
• 39:28
  Speaker 2: to the plane of the galaxy, it's moving fast because
• 39:30
  Speaker 2: it's been tugged on by that gravity and it passes
• 39:33
  Speaker 2: through it, and then the galaxy slows it down as
• 39:36
  Speaker 2: it goes through the bottom and turns it around and
• 39:38
  Speaker 2: pulls it back. So it's basically like a pendulum. The
• 39:41
  Speaker 2: Sun is oscillating around the center of the galaxy over
• 39:44
  Speaker 2: like a thirty million year cycle.
• 39:47
  Speaker 1: So does that mean that if you look out that
• 39:49
  Speaker 1: like for the dinosaurs, some of the stars were higher
• 39:52
  Speaker 1: in the sky and then later they're lower in the
• 39:54
  Speaker 1: sky or no, because the Milky Way moves all as
• 39:57
  Speaker 1: one and it's the rest of the stuff that moving
• 40:00
  Speaker 1: relative to us.
• 40:01
  Speaker 2: Yeah, it's a great question. It's not that the Milky
• 40:03
  Speaker 2: Way moves all at one, right, It is all these
• 40:05
  Speaker 2: blobs of kinematic groups that are moving, and the Sun
• 40:08
  Speaker 2: is basically moving through it. And so as we go down,
• 40:11
  Speaker 2: all the stars that are near us change and then
• 40:13
  Speaker 2: we come back up. Some of those are oscillating on
• 40:16
  Speaker 2: different cycles than hours, So like every thirty million years,
• 40:19
  Speaker 2: you like go into water and come back up, things
• 40:21
  Speaker 2: can really have changed. In the meantime. We're not the
• 40:24
  Speaker 2: only star that does this kind of oscillation, so there's
• 40:27
  Speaker 2: a sort of a lot of change in our galactic
• 40:29
  Speaker 2: neighborhood on a million year timescale.
• 40:31
  Speaker 1: I feel like I've never wanted a time machine more
• 40:34
  Speaker 1: than during this conversation. It would be so cool to
• 40:37
  Speaker 1: see this stuff.
• 40:38
  Speaker 2: There's another really interesting effect just from the rotation of
• 40:41
  Speaker 2: the galaxy. Like you look at the galaxy like Andromeda
• 40:44
  Speaker 2: or most galaxies, you see that they have these arms. Right,
• 40:47
  Speaker 2: there's the central bar and then these arms where the
• 40:49
  Speaker 2: stars are denser than other things. And we know that
• 40:52
  Speaker 2: galaxies are rotating. I think that most people imagine those
• 40:56
  Speaker 2: arms to be like physical structures. They have a bunch
• 40:58
  Speaker 2: of stars in them, and as it rotates, those stars
• 41:01
  Speaker 2: all move together the way like if you spin your
• 41:04
  Speaker 2: arm around your body, all the cells in your arm
• 41:07
  Speaker 2: move together, right, your arm stays together. But the galaxy's
• 41:10
  Speaker 2: arms are not like that at all. Those arms are
• 41:12
  Speaker 2: not physical structures. They're density waves. They're more like if
• 41:16
  Speaker 2: you go to a football game and people do the
• 41:18
  Speaker 2: wave right, the wave moves through the crowd, but the
• 41:21
  Speaker 2: crowd doesn't move right. It's those people's arms going up
• 41:25
  Speaker 2: and down that creates this impression of a wave.
• 41:27
  Speaker 1: And there's always those people that don't keep up.
• 41:30
  Speaker 2: Exactly and that's what's happening in the galaxy. It's not
• 41:33
  Speaker 2: that the stars in those arms are all moving together. Instead,
• 41:37
  Speaker 2: there's a density wave with things pulled together, and then
• 41:39
  Speaker 2: that dense blob moves through the galaxy. So it's sort
• 41:43
  Speaker 2: of like a traffic pattern, right, you know, like when
• 41:45
  Speaker 2: you're driving on the freeway and somebody slams on their
• 41:47
  Speaker 2: brakes and then the cars bunch up and then they
• 41:49
  Speaker 2: speed up, but the cars that were behind them end
• 41:51
  Speaker 2: up bunching up at the same place. Right. So stars
• 41:55
  Speaker 2: are moving through this density wave and then out of
• 41:58
  Speaker 2: the density wave on the other side, which means something
• 42:00
  Speaker 2: really interesting for star watching. It means that sometimes you're
• 42:03
  Speaker 2: in the arm, which means there are more stars near you,
• 42:06
  Speaker 2: and sometimes you're out of the arm, which means there
• 42:08
  Speaker 2: are fewer stars visible to you.
• 42:11
  Speaker 1: WHOA, Okay, So what kind of time skills are we
• 42:14
  Speaker 1: talking about? How long does it take to get in
• 42:15
  Speaker 1: or out of the arm.
• 42:16
  Speaker 2: So the Sun is actually moving through the galaxy like
• 42:19
  Speaker 2: twice as fast as the arm, so we like pass
• 42:23
  Speaker 2: through the arm and out the other side. So the
• 42:25
  Speaker 2: Sun is moving like twenty nine kilometers per second through
• 42:28
  Speaker 2: the galaxy and these density wave arms are moving like
• 42:31
  Speaker 2: seventeen kilometers per second, but they're pretty big, So we're
• 42:35
  Speaker 2: talking like tens of millions of years to go through
• 42:38
  Speaker 2: the density wave. It also means something really cool about
• 42:41
  Speaker 2: beyond the galaxy. Right, the galaxy rotates every two hundred
• 42:45
  Speaker 2: and fifty million years on average, and the dinosaurs lived,
• 42:48
  Speaker 2: you know, like one hundred and fifty to two hundred
• 42:50
  Speaker 2: million years ago. That means that the dinosaurs basically lived
• 42:53
  Speaker 2: on the other side of the galaxy, or like when
• 42:56
  Speaker 2: the galaxy was spun around halfway around, right.
• 42:59
  Speaker 8: I have to say.
• 43:02
  Speaker 2: And so even though we can't see beyond the galaxy
• 43:05
  Speaker 2: with the naked eye, our view of other galaxies has
• 43:09
  Speaker 2: changed completely in one hundred million years. We're like looking
• 43:12
  Speaker 2: at a completely different part of the universe. When we
• 43:15
  Speaker 2: look out from our galaxy is as big a difference
• 43:19
  Speaker 2: as like winter and summer galaxies. Right, you're just looking
• 43:21
  Speaker 2: at a completely different part of the sky. So dinosaur
• 43:24
  Speaker 2: has basically evolved on the other side of the galaxy.
• 43:27
  Speaker 2: They were never here, right, Those dinosaurs never existed in
• 43:31
  Speaker 2: this part of the galaxy.
• 43:32
  Speaker 1: I'll be honest. When we said we were going to
• 43:35
  Speaker 1: do this topic, I thought like maybe there'll be some
• 43:37
  Speaker 1: more stars or fewer stars, and maybe things have shifted around.
• 43:41
  Speaker 1: I did not expect the answer to be the sixth Street.
• 43:44
  Speaker 2: There's some other fun effects too that I want to
• 43:46
  Speaker 2: get into that the listeners talked about. Somebody mentioned the
• 43:48
  Speaker 2: expansion of the universe, right, because the universe is getting bigger,
• 43:53
  Speaker 2: and that expansion is happening faster and faster every year,
• 43:57
  Speaker 2: and so that's true that galaxies are getting fir away.
• 44:00
  Speaker 2: And again, we can't see galaxies with the naked eye,
• 44:03
  Speaker 2: and the dinosaurs definitely didn't have the technology. But it's
• 44:05
  Speaker 2: interesting to imagine, like, could those galaxies have been closer
• 44:09
  Speaker 2: during the dinosaurs times? Could maybe they have seen them
• 44:12
  Speaker 2: with the naked eye? Well, the answer is, unfortunately probably not.
• 44:15
  Speaker 2: The structure of the universe on a really really big
• 44:18
  Speaker 2: scale is dominated by dark energy, this thing tearing the
• 44:21
  Speaker 2: universe apart, making it expand. But the organization of our
• 44:24
  Speaker 2: galaxy and the neighboring galaxies altogether is mostly just dominated
• 44:28
  Speaker 2: by gravity. Like, dark energy is not powerful enough to
• 44:32
  Speaker 2: really affect the structure of our galaxy or of our
• 44:35
  Speaker 2: relationship with nearby galaxies, like Andromeda is headed towards us,
• 44:40
  Speaker 2: despite dark energy expanding the space between us, because gravity
• 44:44
  Speaker 2: on that scale is more powerful than dark energy. Shorter
• 44:48
  Speaker 2: distances like between galaxies, gravity dominates, and longer distances like
• 44:52
  Speaker 2: between clusters of galaxies, that's when dark energy really takes over.
• 44:56
  Speaker 2: The other issue is that like two hundred and fifty
• 44:58
  Speaker 2: million years sounds like a long time, but it's only
• 45:01
  Speaker 2: like two percent of the age of the universe, so
• 45:04
  Speaker 2: there hasn't really been time for dark energy to dramatically
• 45:08
  Speaker 2: change the arrangements of galaxies in that time.
• 45:11
  Speaker 1: Well, there's one difference in the night sky that I'm
• 45:14
  Speaker 1: sure the dinosaurs. I don't know how good or bad
• 45:16
  Speaker 1: their vision was, but I'm sure they didn't miss this.
• 45:19
  Speaker 1: How about that asteroid.
• 45:23
  Speaker 2: That asteroid probably was totally visible to the t rexes
• 45:27
  Speaker 2: and whoever else was around, And they're proto astronomers. We
• 45:31
  Speaker 2: imagine that asteroid was probably moving around thirty kilometers per second,
• 45:35
  Speaker 2: which means that if it's approaching the Earth, it gets
• 45:38
  Speaker 2: closer by like two point six million kilometers every single day.
• 45:43
  Speaker 2: And they've actually done a reconstruction to think like how
• 45:45
  Speaker 2: far away was it when it was visible? And they
• 45:48
  Speaker 2: think that probably it was visible to the naked eye
• 45:51
  Speaker 2: for like three days before it actually entered the atmosphere,
• 45:55
  Speaker 2: because it probably reflected enough sunlight to be visible in
• 45:58
  Speaker 2: the night sky. It's like, huh, what's that? And so
• 46:01
  Speaker 2: you know, if they've been paying attention, they had at
• 46:04
  Speaker 2: least three days to build their bunkers.
• 46:06
  Speaker 1: Oh boy, I don't think that's enough time.
• 46:08
  Speaker 2: It's detainly not enough time, which is why dinosaurs needed
• 46:11
  Speaker 2: to really fund their astronomy programs and think about this
• 46:14
  Speaker 2: stuff so they have like more warning before something hit them.
• 46:18
  Speaker 1: Absolutely, But you know that's.
• 46:19
  Speaker 2: A moral question, Like if you go back in time
• 46:21
  Speaker 2: in your time machine to the dinosaur time, should you
• 46:24
  Speaker 2: lobby dinosaur Congress to fund astronomy which might prevent the
• 46:27
  Speaker 2: evolution of mammals and you and your kids?
• 46:30
  Speaker 1: I think they might just eat that's my biologist perspective here.
• 46:34
  Speaker 2: Even if you come with valuable information, they're just going
• 46:36
  Speaker 2: to gobble you up.
• 46:37
  Speaker 1: Yeah, you know, I think probably that's how it would go.
• 46:40
  Speaker 2: I guess there's a good lesson there. You know, if
• 46:42
  Speaker 2: we get visitors from the future, you know, future reptiles
• 46:46
  Speaker 2: or whatever is going to replace humans when we kill ourselves,
• 46:48
  Speaker 2: we shouldn't just eat them. We should listen to them first,
• 46:50
  Speaker 2: that's what you're saying.
• 46:51
  Speaker 1: Yeah, don't eat the visitors.
• 46:53
  Speaker 2: That's right, and that's the lesson for your kids. You
• 46:56
  Speaker 2: know that we should fund astronomy today so that we
• 46:58
  Speaker 2: can be better prepared than the dinosaur were when they
• 47:01
  Speaker 2: looked up at their night sky. And also, don't eat
• 47:04
  Speaker 2: the future time traveling werewolves.
• 47:05
  Speaker 1: Oh my gosh. We covered a lot of ground today,
• 47:09
  Speaker 1: both fictional and otherwise.
• 47:11
  Speaker 2: So I think it's really fun to think about the
• 47:13
  Speaker 2: depth of the night sky and how it changes over time.
• 47:17
  Speaker 2: And it's sort of cool this coincidence that, like, astronomical
• 47:21
  Speaker 2: time scales are very very different from the time scales
• 47:23
  Speaker 2: of a human lifetime or even human history, but they
• 47:27
  Speaker 2: do kind of line up with archaeological time scales. Right
• 47:30
  Speaker 2: when we think about the dinosaurs one hundred two hundred
• 47:33
  Speaker 2: million years ago, that's long enough to really see a
• 47:36
  Speaker 2: change in our astronomical neighborhood.
• 47:39
  Speaker 1: Quite a big change.
• 47:41
  Speaker 2: Quite a big change indeed. All right, thanks very much
• 47:43
  Speaker 2: everybody for coming along on this tour of deep time
• 47:46
  Speaker 2: and this trip into our imagination for what dyn astronomers
• 47:50
  Speaker 2: might have seen. And thanks very much to Kelly for
• 47:52
  Speaker 2: going along and laughing at our time traveling were wolf jokes.
• 47:55
  Speaker 1: Thanks for having me. It was a blast as always, all.
• 47:58
  Speaker 2: Right everyone, Thanks for listening to and in next time,
• 48:08
  Speaker 2: thanks for listening and remember that Daniel and Jorge Explain
• 48:11
  Speaker 2: the Universe is a production of iHeartRadio. For more podcasts
• 48:15
  Speaker 2: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
• 48:20
  Speaker 2: you listen to your favorite shows.