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Speaker 1: Daniel, how's it going.

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Speaker 2: I'm good.

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Speaker 3: Good.

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Speaker 2: Nice to talk to you again.

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Speaker 1: Yeah, nice to talk to you too. You know, I

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Speaker 1: was out the other day and one of the great

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Speaker 1: things about living in the country is that when there's

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Speaker 1: a cloudless sky, you really get to look up at

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Speaker 1: the stars and see all the night sky. And I've

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Speaker 1: been looking out there with my oldest kiddo lately, and

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Speaker 1: I was wondering, do you and your kids like looking

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Speaker 1: up at the stars too?

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Speaker 2: You know, I'm more into astronomy than they are, but

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Speaker 2: back when they were younger, we did a lot of

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Speaker 2: star watching.

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Speaker 1: Awesome, So you asked a lot of questions, and so

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Speaker 1: I wonder if your kids are like you, do they

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Speaker 1: ask you some really cool questions?

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Speaker 2: They did, yes, sometimes some surprising questions and sometimes some

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Speaker 2: kind of like embarrassing questions.

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Speaker 1: Embarrassing what could possibly be embarrassing about the night sky?

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Speaker 2: Well, I remember telling them that the stars are really old,

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Speaker 2: like super duper old, like crazy old, okay, And then

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Speaker 2: their follow up question was, oh, really old? You mean

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Speaker 2: like you and mommy?

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Speaker 1: Oh out, kids are cruel, I know.

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Speaker 2: So I had to explain to them that we were

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Speaker 2: incredibly old, but not like astronomically cosmically old, not quite yet.

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Speaker 1: It's a different scale entirely.

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Speaker 4: Really.

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Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor

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Speaker 2: at UC Irvine, and I like to think of myself

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Speaker 2: as not astronomically old.

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Speaker 1: I'm Kelly Wiener Smith. I'm adjunct at Race University. And

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Speaker 1: my daughter asked the other day when I couldn't hear

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Speaker 1: what she was saying, if that was because I was

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Speaker 1: getting old, and sometimes old people lose their hearing. I

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Speaker 1: also prefer to think of myself is not astronomically old,

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Speaker 1: but maybe old by people's standards. Who knows.

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Speaker 2: And so, what did you say? Did you say? Huh?

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Speaker 5: What?

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Speaker 2: I didn't hear you?

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Speaker 1: Now I think I just gave her the stink guy.

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Speaker 2: That's a very powerful nonverbal communication.

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Speaker 1: That's right, that's right.

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Speaker 2: But one thing that's wonderful about the night sky and

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Speaker 2: about the universe is that it does inspire the sort

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Speaker 2: of kiddo's sense of wonder in all of us looking

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Speaker 2: up at the stars and wondering what they are and

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Speaker 2: how they work. It's sort of like a common thread

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Speaker 2: through all of human existence, probably going back thousands of years.

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Speaker 1: It's true. Probably some of the most profound and the

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Speaker 1: most wish I was able to be profound statements have

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Speaker 1: been said while looking at the night sky.

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Speaker 2: And Welcome to the podcast Daniel and Jorge Explain the

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Speaker 2: Universe in which we try to be profound about the

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Speaker 2: nature of the universe. We stare out into the vast

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Speaker 2: cosmos and wonder how does it all work? What's going

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Speaker 2: on out there? Can we make makes sense of any

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Speaker 2: of it or all of it or none of it?

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Speaker 2: And so on this podcast we dig deep into the

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Speaker 2: mysteries of the universe and try to explain all of

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Speaker 2: them to you. My friend and regular co host Jorge

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Speaker 2: can't be here today, but I'm very happy to be

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Speaker 2: talking about the nature of the night sky with my

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Speaker 2: friend Kelly. Kelly, thanks very much for joining us.

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Speaker 1: Thanks, I'm happy to be here, and I'm keeping my

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Speaker 1: fingers crossed that we don't talk about anything that's going

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Speaker 1: to scare me or my kids today, So I guess

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Speaker 1: we'll see what happens.

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Speaker 2: We're going to talk about fun stuff today, but we're

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Speaker 2: also going to talk about big cataclysmic events. Oh uh oh, yeah, exactly,

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Speaker 2: and we are going to try to touch back on

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Speaker 2: that sense of all and wonder that we have when

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Speaker 2: we look up at the night sky. Because something that

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Speaker 2: I love when I see the night sky is thinking

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Speaker 2: about how other humans saw it, you know, cave people

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Speaker 2: or even proto humans looking up at the stars, wondering

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Speaker 2: what they were, not realizing how many secrets about the

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Speaker 2: nature of the universe they contained, the messages that are

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Speaker 2: coming to us from outer space telling us about how

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Speaker 2: the universe works.

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Speaker 1: Yeah, I wonder if it was mostly scary or mostly

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Speaker 1: like relaxing to look up at the night sky back

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Speaker 1: when we had no idea what it was.

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Speaker 2: Probably some combination of both. I had an amazing experience

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Speaker 2: a few years ago because I got to be in

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Speaker 2: the path of totality for the most recent eclipse that

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Speaker 2: went through North America. And I was excited about it

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Speaker 2: because you know, I'm a space nerd, but frankly, I

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Speaker 2: was preparing to be a little bit underwhelmed. Like you know,

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Speaker 2: fireworks and Fourth of July, for example, we've all seen

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Speaker 2: them before. It's exciting, I guess, but it doesn't really

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Speaker 2: blow your socks off. I was sort of expecting that

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Speaker 2: kind of experience, but I was totally surprised and amazed

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Speaker 2: at the depth of the experience, the like really shocking

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Speaker 2: overwhelming nature of that experience, And part of it was

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Speaker 2: thinking about what it must have been like for ancient

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Speaker 2: peoples to have something like really central in their existence,

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Speaker 2: the sun just like go away for a few minutes.

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Speaker 2: What must have that been like if you didn't have

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Speaker 2: any understanding about what was happening.

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Speaker 1: And I think it impacts more than just humans, Like

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Speaker 1: I've heard that in some of the areas when the

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Speaker 1: sun goes away in the middle of the day, insects

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Speaker 1: will start chirping like it's nighttime, like even their kind

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Speaker 1: of thrown like it's nighttime and the nighttime has gone

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Speaker 1: away again, and what is the world doing. I don't

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Speaker 1: know if they have a stress response, but it seems

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Speaker 1: to throw all of us off.

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Speaker 2: It is very strange, and it makes me very glad

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Speaker 2: that we have some understanding of why it happens, so

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Speaker 2: we don't all have to be terrified that like the

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Speaker 2: basic deal in which we live is suddenly changed for

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Speaker 2: reasons we don't understand. And I understand now, like why

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Speaker 2: the Chinese and the Babylonians and the Mayans were so

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Speaker 2: intent on understanding what was going on in the cosmos

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Speaker 2: and keeping track of it and trying to predict the

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Speaker 2: clipses and all this kind of stuff.

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Speaker 3: Yeah.

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Speaker 2: Absolutely, it's super fun actually to dig in the details

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Speaker 2: of like how the Greeks did astronomy and how the

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Speaker 2: Chinese did astronomy without understanding geometry and all this kind

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Speaker 2: of stuff. Super fascinating things we can dig into on

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Speaker 2: another episode, But today we want to go even further back.

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Speaker 2: Not just wondering if ancient Chinese and Babylonian astronomers were

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Speaker 2: looking at at the same night sky as we were

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Speaker 2: and having the same feelings of on wonder, We want

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Speaker 2: to go deep, deep into the real history of the

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Speaker 2: Earth and wonder like, what did the night sky look

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Speaker 2: like a million years ago, fifty million years ago? How

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Speaker 2: much does it change? After all?

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Speaker 1: That's so, how far back are we going?

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Speaker 2: So on today's episode we're going to ask the question

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Speaker 2: what did the night sky look like to the dinosaurs?

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Speaker 2: Whoa exactly if you were a dinosaur astronomer, I guess

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Speaker 2: that would be like a dino astronomer or an astronosaurus.

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Speaker 2: I'm not sure what you would call that. What would

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Speaker 2: you see if you looked up at the night sky.

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Speaker 2: Are we looking up at basically the same night sky

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Speaker 2: as a dinosaurs or did the dinosaurs live long enough

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Speaker 2: ago that enough cosmic time has elapsed that things could

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Speaker 2: actually look different.

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Speaker 1: Well, you asked a bunch of smart people this question.

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Speaker 1: Should we see what they had to say?

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Speaker 2: I did exactly that. Thank you very much to our

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Speaker 2: listeners who participate in this segment of the podcast, giving

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Speaker 2: us a sense for what people out there know and

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Speaker 2: do not know about the question of the day. So

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Speaker 2: thanks very much to everybody who participates. If you would

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Speaker 2: like to hear your voice speculating basisly on the podcast,

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Speaker 2: please write to me two questions at Danielandjorge dot com.

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Speaker 2: Everybody is welcome. So before you hear these listeners' answers,

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Speaker 2: think to yourself, do you think astronosauruses were studying the

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Speaker 2: same night sky as we were?

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Speaker 5: Well, that's an interesting question. I know that the constellations

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Speaker 5: that we see in the sky are not static. The

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Speaker 5: universe is moving, The galaxy is moving, our Solar system

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Speaker 5: is moving with respect to the other stars. It's just

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Speaker 5: it's happening on a very slow scale. So on the

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Speaker 5: scale of Dinas Stares sixty five million years ago. They

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Speaker 5: probably didn't see the same constellations that we see. Some

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Speaker 5: of the stars that we see today probably they saw

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Speaker 5: as well, but they probably saw other stars that are

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Speaker 5: no longer there.

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Speaker 6: I'm guessing that the night sky looked quite similar. However,

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Speaker 6: some stars were likely brider on account that the universe

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Speaker 6: hadn't expanded as much.

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Speaker 3: I don't think the sky looked really different for dinosaurs.

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Speaker 3: I mean, sixty five million years not a lot for

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Speaker 3: the universe, so I think the skyes looked pretty much

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Speaker 3: the same, maybe a little more stars here and there,

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Speaker 3: not so different.

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Speaker 7: I think in the time of the dinosaurs, this night

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Speaker 7: sky probably looked a bit more condensed with stars like

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Speaker 7: the constellations were maybe more close together, although there were

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Speaker 7: other stars that were visible that on anymore.

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Speaker 4: I can't imagine there'd be a lot of light pollution,

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Speaker 4: so you'd get to see a lot more stars, probably

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Speaker 4: different nebulas than we have now, different constellations, and I

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Speaker 4: can imagine there was an asteroid approaching at one point.

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Speaker 8: I think that the sky for dinos, the night sky

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Speaker 8: for Dino's would look like filled with more stars because

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Speaker 8: then there was no light pollution and distant galaxies were

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Speaker 8: slightly closer to worth some billion years ago.

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Speaker 1: So I was really surprised by how diverse the answers

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Speaker 1: were here. There's a lot of different you know, the

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Speaker 1: answers ranged from pretty much nothing has probably changed to

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Speaker 1: different stars. And I hadn't actually even considered that maybe

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Speaker 1: our conversation would include light pollution. So I thought that

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Speaker 1: was an interesting thing to include and a very good point.

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Speaker 1: But yeah, so they you know, they were thinking about

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Speaker 1: what are Cosmolalasaurus. There's got to be a way to

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Speaker 1: shorten it, but what they were looking at, So, can

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Speaker 1: can you give me a sense of like how long

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Speaker 1: ago we were talking here with the dinosaurs?

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Speaker 2: Yeah, so the dinosaurs are really deep in the past, right.

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Speaker 2: We're used to thinking about humans arising fifty one hundred

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Speaker 2: thousand years ago and the evolution of our ancestors over

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Speaker 2: the last few million years. But dinosaurs, we think were

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Speaker 2: wiped out about sixty five million years ago, and they

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Speaker 2: lasted for a long long time before that. We're talking

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Speaker 2: about like the Triassic Period started about two hundred and

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Speaker 2: fifty million years ago Jurassic, which is when we had

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Speaker 2: like stegosauruses like two hundred million years ago, and then

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Speaker 2: the Cretaceous period when we had like the t rex

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Speaker 2: and the triceratops, that's like one hundred and fifty million

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Speaker 2: years ago till about when that asteroid hit like sixty

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Speaker 2: five million years ago, So that's like really a long

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Speaker 2: time compared to human existence, though of course it's still

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Speaker 2: pretty short compared to like the age of the universe,

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Speaker 2: which is fourteen billion years, and even the age of

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Speaker 2: the Earth, which is four and a half billion years.

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Speaker 2: One of my favorite things about astronomy is just like

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Speaker 2: the length of these crazy timelines. You know, so much

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Speaker 2: happens on Earth in basically the blink of an eye

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Speaker 2: from the point of view of the cosmos.

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Speaker 1: And I am so bad thinking about like units and

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Speaker 1: how to compare them. Like, you know, my husband laughs

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Speaker 1: if we have to say, you know, oh, how much

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Speaker 1: is two inches, He'll be like, no, no, don't even ask Kelly,

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Speaker 1: because I'll be like us anywhere from you know, like

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Speaker 1: I don't know, my fingers are showing like a foot

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Speaker 1: to a centimeter, and I'm just like, I'm pretty bad

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Speaker 1: at this stuff. So my brain has a little trouble

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Speaker 1: wrapping itself around questions like this. So, so how do

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Speaker 1: we start thinking about this question.

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Speaker 2: Yeah, I think maybe we should start by thinking about

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Speaker 2: what we are seeing in the night sky, like what

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Speaker 2: is up there that we can see, and then we

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Speaker 2: can dig back into the past and think about how

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Speaker 2: things are changing, because you're right, the listeners give us

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Speaker 2: a lot of really cool clues, like thinking about light

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Speaker 2: pollutions and the expansion of the universe and the constellations,

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Speaker 2: and I think there's a lot of great stuff to

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Speaker 2: dig into. But maybe we should start with what we're

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Speaker 2: seeing in the night sky, like what is up there

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Speaker 2: in the night sky for us to see? When you

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Speaker 2: stand out there with your kids staring up the night sky,

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Speaker 2: sip in your hot coco, what is it exactly that

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Speaker 2: you're seeing? And I think people will be surprised to

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Speaker 2: learn what we're seeing and what we're not seeing. Like

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Speaker 2: if you ask people how many stars are visible in

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Speaker 2: the night sky, they typically come up with like really

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Speaker 2: big numbers, thousands and thousands, millions and millions of stars,

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Speaker 2: because they know that there are lots of stars out

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Speaker 2: there in the universe, but when you look up at

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Speaker 2: the night sky, they're only about a few thousand that

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Speaker 2: you can see with the naked eye.

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Speaker 1: WHOA. I would have guessed that number was much bigger,

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Speaker 1: and so is we talking like two thousand.

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Speaker 2: So there are nine thousand stars in the Milky Way

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Speaker 2: that are bright enough to see with the naked eye.

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Speaker 2: The brightest one is called Vega, but it's still pretty dim.

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Speaker 2: It's like one hundred and twenty five thousand times dimmer

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Speaker 2: than the full moon, and most of the stars that

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Speaker 2: are out there are like less than a percent as

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Speaker 2: bright as Vega. Now, I don't want to be dissing

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Speaker 2: these stars, right, Remember, these guys are really far away.

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Speaker 2: We're talking about light years or tens of light years

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Speaker 2: or thousands of light years away. So it's amazing that

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Speaker 2: you can see this ball of gas burning from light

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Speaker 2: years and light years away from billions and billions of

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Speaker 2: miles right, Like, that's just another sense of awe. I

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Speaker 2: remember teaching my kids that, like, the Sun is crazy

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Speaker 2: far away, like ridiculously far away, but it's so big

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Speaker 2: that you can still feel it through ninety million miles

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Speaker 2: of space.

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Speaker 3: Right.

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Speaker 2: Even just that fact still amazes me when I think

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Speaker 2: about it. So, these stars are out there, they're burning bright.

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Speaker 2: It's incredible that we can see them over such great distances,

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Speaker 2: But there really are only nine thousand that are capable

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Speaker 2: of being spotted on a given night, and so if

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Speaker 2: you're standing on the earth looking up, you're seeing some

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Speaker 2: fraction of those. So it's really just a few thousand stars.

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Speaker 1: To be honest, this is making me wish that we

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Speaker 1: had another kind of biologist expert on the show right now,

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Speaker 1: like someone who could tell us about eye vision. You know,

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Speaker 1: how many of those nine thousand stars that we can

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Speaker 1: see with our naked eyes do we think that maybe

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Speaker 1: the dinosaurs would have been able to see based on

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Speaker 1: like the size of their eye sockets and what we

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Speaker 1: know about vision and birds and reptiles or something now,

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Speaker 1: But we're gonna have to let that go for now.

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Speaker 2: I Yes, we'll ask Katie that question next time she's

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Speaker 2: on the podcast.

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Speaker 1: There you go.

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Speaker 2: Yes, dinosaurs with glasses, dinosaurs with like binoculars. You know,

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Speaker 2: there's a whole great comic vein to mine there, you know,

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Speaker 2: with t Rex even be able to put glasses on

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Speaker 2: because his arms are so short.

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Speaker 1: Maybe maybe that would favor the evolution of social behavior,

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Speaker 1: you know, so that you could have someone help you

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Speaker 1: put your glass floe or maybe.

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Speaker 2: The reason t Rex has never developed astronomy, was just

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Speaker 2: because they couldn't hold the telescope up to their eyes.

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Speaker 2: Otherwise it might have saved them, right if they had

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Speaker 2: developed astronomy and seen the asteroid coming, boy, life could have.

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Speaker 1: Been different, absolutely so. But we're lucky that they didn't.

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Speaker 2: We are we are all lucky. We have no complaints

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Speaker 2: about the history as it happened. But you know, we

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Speaker 2: know that there are other things up there in the

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Speaker 2: night sky as well, right like we know that the

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Speaker 2: galaxy is just one of many galaxies in the universe,

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Speaker 2: and we're used to talking about the other galaxies here

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Speaker 2: on the podcast and how the universe is expanding. We're

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Speaker 2: part of a cluster and a supercluster and et cetera.

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Speaker 2: But the interesting thing is that when you look up

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Speaker 2: at the night sky, you mostly can't see those other galaxies.

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Speaker 2: I mean, this is an incredible number of them, but

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Speaker 2: they're really, really, really far away. It takes special equipment

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Speaker 2: to see them. You might imagine, for example, the Hubble

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Speaker 2: deep field. That's this famous picture where the Hubble focused

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Speaker 2: on a single spot in the sky for a long time,

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Speaker 2: gathered all those fained photons and it came away with

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Speaker 2: this shocking image. Shocking because it's so chock full of galaxies.

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Speaker 2: It's just like grains of sand on the beach. You know,

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Speaker 2: there's just galaxies everywhere, but you can't see them mostly,

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Speaker 2: and you definitely can't see them with the naked eye

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Speaker 2: because so few photons arive from them that you need

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Speaker 2: like a really big aperture and a really long time

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Speaker 2: to even see a single photon from those distant galaxies.

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Speaker 1: And the dinosaurs definitely didn't have the web telescope.

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Speaker 2: So and there's something really interesting and sort of quantum

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Speaker 2: mechanical there that some listeners write in and ask me about.

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Speaker 2: They like to think about the photons flying away from

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Speaker 2: that galaxy. And you know, in principle they're flying in

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Speaker 2: every direction, but photons are discrete, right, They're little bundles,

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Speaker 2: and so they fly like in one direction and in

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Speaker 2: not another, which means if you're really close up to

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Speaker 2: the galaxy, you're getting lots of photons from it, But

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Speaker 2: as you get further and further away, there can start

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Speaker 2: to be gaps places where like no photon from that

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Speaker 2: galaxy is now arriving. You wait long enough, eventually you'll

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Speaker 2: get lucky and a photon will spray out in just

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Speaker 2: your direction to fly across the universe and hate your eyeball.

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Speaker 2: But you're not guaranteed. Right. There are moments where there

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Speaker 2: are zero photons arriving from a distant galaxy, and that's

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Speaker 2: why you just can't see them. You need to wait

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Speaker 2: long enough, or like point Hubble at it long enough

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Speaker 2: to sort of integrate enough photons. These things emerge from

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Speaker 2: the blacknest.

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Speaker 1: Like a cosmic invisibility sort of.

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Speaker 2: And even the nearby galaxies are not easy to spot,

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Speaker 2: like our neighbor Andromeda. It's a few million light years away,

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Speaker 2: but it's a huge monster galaxy. It's much bigger than

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Speaker 2: our galaxy. In fact, it's so big that if you

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Speaker 2: could see it, it would be larger in the sky

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Speaker 2: than the full moon. Whoa, yeah, but it's just not

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Speaker 2: that bright because it's so far away, so it's basically

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Speaker 2: invisible to the naked eye. But you know, you set

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Speaker 2: up a telescope and point it in the right spot

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Speaker 2: for long enough, you can get really amazing pictures of Andromeda.

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Speaker 2: And I feel like that would change our whole concept

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Speaker 2: of galaxies and what they are. If we could have

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Speaker 2: seen Andromeda imagine just like having another galaxy out there

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Speaker 2: for us to look at from the outside would have

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Speaker 2: given us such a huge clue about like what was

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Speaker 2: going on out there in the universe.

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Speaker 1: I can also imagine that, yeah, being very scary if

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Speaker 1: you didn't know what it was.

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Speaker 2: That's true. And you know, it was only like a

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Speaker 2: one hundred years ago that Hubble realized that there are

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Speaker 2: other galaxies out there. Until then, we thought our galaxy

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Speaker 2: was the only one just floating out there in space.

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Speaker 2: And it's when Hubble realized that those little smudges that

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Speaker 2: were just barely visible in his telescopes were actually super

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Speaker 2: duper far away. He and some other astronomers developed a

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Speaker 2: way to measure the distance to them. That's when he realized, oh,

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Speaker 2: those little smudges are actually entire other galaxies, super far away.

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Speaker 2: That's how hard they are to see and to study,

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Speaker 2: and how recently we've understood that they're even there. So

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Speaker 2: our ancestors, Chinese astronomers, Babylonian astronomers had no idea that

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Speaker 2: there were other galaxies up there in the night sky.

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Speaker 1: And this is why it's great that we fund science

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Speaker 1: more now. So that's what things look like now. Let's

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Speaker 1: take a break, and when we get back, let's talk

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Speaker 1: about how that view changes over time. Okay, so we

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Speaker 1: talked about how we can see about nine thousand stars

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Speaker 1: in the sky with our naked eye, and some of

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Speaker 1: them are pretty dim and stuff that's far away is

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Speaker 1: too faint to see, including galaxies. How did that view

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Speaker 1: change over time?

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Speaker 2: So there's a lot of really interesting aspects here. You know,

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Speaker 2: there is a questioning of light pollution. There's the question

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Speaker 2: of the moon. There's how the constellations might change. There's

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Speaker 2: how the galaxy rotates. There's the expansion of the universe.

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Speaker 2: There's asteroids, you know, coming to hit the Earth that

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Speaker 2: we or dinosaurs might have spotted. So let's take them

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Speaker 2: one at a time and dig into each one and

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Speaker 2: think about how it impacts our view of the night

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Speaker 2: sky and the dinosaur's view of the night sky. The

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Speaker 2: first one, because I love this response from the listeners, is,

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Speaker 2: of course light pollution right now. Clearly, if you're living

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Speaker 2: in New York City or a big city and you

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Speaker 2: look by the night sky, you're not seeing a whole

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Speaker 2: lot of stars. Maybe you saw the recent conjunction of

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Speaker 2: Jupiter and Venus. Maybe you see the North Star. But

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Speaker 2: you know, just most of the stars out there are

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Speaker 2: sort of overshadowed by the light from your city. And

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00:20:03,359 --> 00:20:05,240
Speaker 2: this happens during the day too, right, you look up

403
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Speaker 2: at the sky during the day. The stars are there,

404
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Speaker 2: they're sending photons at you. It's just that you can't

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Speaker 2: see them because they're not overshadowed. It's the word over

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00:20:13,320 --> 00:20:16,439
Speaker 2: photon or out shown. There you go, they're out shown

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Speaker 2: by the sun. They go, You're blinded by the light

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Speaker 2: of the sign and so you just can't see them.

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Speaker 2: And you know, we imagine dinosaurs, of course, did not

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Speaker 2: build large metropolises, you know, or metropolisauruses, and so they

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Speaker 2: didn't have light pollution. Unless you're a believer in like

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Speaker 2: you know, atlantis or like ancient aliens or some other

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Speaker 2: kind of nonsense.

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Speaker 1: That's for a different show, a different show.

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Speaker 2: That's for a different show where it's sticking to the

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Speaker 2: actual science here. Then probably the dinosaurs didn't have to

417
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Speaker 2: contend with light pollution, and so they could see the

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Speaker 2: night sky as well as we can under the best circumstances.

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Speaker 2: And while if you live in a city, you're not

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Speaker 2: seeing it under the best circumstances. There's still a lot

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Speaker 2: of places in the country and in the world you

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Speaker 2: can go to get a pretty good dark sky. It's

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Speaker 2: unfortunately getting smaller and smaller as humans encroach on every

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Speaker 2: last piece of the planet, but it is still possible,

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Speaker 2: and if you go camping you can get a pretty

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Speaker 2: good dark sky experience.

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Speaker 1: I consider this one of the biggest perks of living

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Speaker 1: out in the middle of nowhere is the uh, the

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Speaker 1: lower light pollution.

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Speaker 2: Yeah, and if you're not somebody who regularly sees that

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Speaker 2: kind of sky, it can be kind of alarming or

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00:21:23,720 --> 00:21:26,439
Speaker 2: shocking or just you know, awe inspiring. If you do

433
00:21:26,560 --> 00:21:28,600
Speaker 2: go out camping and you look up, you're like, wow,

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Speaker 2: all these stars are here, like all the time. It's

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Speaker 2: an incredible view, and I think most people underappreciate it.

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Speaker 2: You know, you stand on like the top floor the

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Speaker 2: Empire State Building, You're like, Wow, what a view I

438
00:21:40,840 --> 00:21:43,560
Speaker 2: can see for miles right. Well, if you look up

439
00:21:43,560 --> 00:21:46,840
Speaker 2: in the night sky, you're seeing for billions of miles, Like,

440
00:21:47,080 --> 00:21:50,080
Speaker 2: what a view that is. You know, it's incredible and

441
00:21:50,119 --> 00:21:53,159
Speaker 2: we're so lucky that it even exists, that everything is

442
00:21:53,160 --> 00:21:55,080
Speaker 2: set up in the universe for there to be stars

443
00:21:55,080 --> 00:21:57,879
Speaker 2: that shines photons and for it to be mostly transparent

444
00:21:57,920 --> 00:22:00,000
Speaker 2: so that light can get to us. I'm like totally

445
00:22:00,040 --> 00:22:02,480
Speaker 2: proselytizing for astronomy here, but I just feel like people

446
00:22:02,480 --> 00:22:04,320
Speaker 2: don't experience and appreciate that enough.

447
00:22:04,480 --> 00:22:07,160
Speaker 1: I think it's one of the greatest experiences in life

448
00:22:07,200 --> 00:22:09,639
Speaker 1: when you get a really good clear night sky. I

449
00:22:09,680 --> 00:22:11,560
Speaker 1: was in Costa Rica once and I could see it

450
00:22:11,600 --> 00:22:13,760
Speaker 1: was the clearest I've ever seen the night sky. And

451
00:22:13,800 --> 00:22:17,360
Speaker 1: it was my job to tend the turtles that were hatching,

452
00:22:17,840 --> 00:22:21,760
Speaker 1: and so I would like see shooting stars and then

453
00:22:22,200 --> 00:22:24,359
Speaker 1: help some turtles get to the ocean. And it was

454
00:22:24,480 --> 00:22:28,439
Speaker 1: like the greatest mix of space and biology, like like

455
00:22:28,520 --> 00:22:31,240
Speaker 1: my two loves coming together at once, and it was

456
00:22:31,280 --> 00:22:33,400
Speaker 1: the happiest I think I've ever been anyway.

457
00:22:34,520 --> 00:22:37,000
Speaker 2: Well, something that could really impact your ability to see

458
00:22:37,000 --> 00:22:39,880
Speaker 2: the stars in the sky is the moon. You want

459
00:22:39,920 --> 00:22:42,520
Speaker 2: to have like a really good dark night experience, you

460
00:22:42,560 --> 00:22:45,400
Speaker 2: need a new moon because the moon is crazy bright.

461
00:22:45,440 --> 00:22:47,919
Speaker 2: As we said, it's like thousands and thousands of times

462
00:22:47,920 --> 00:22:51,080
Speaker 2: brighter than even the brightest star in the sky, so

463
00:22:51,080 --> 00:22:54,040
Speaker 2: it can really spoil in her dark night. But it's

464
00:22:54,080 --> 00:22:56,639
Speaker 2: also interesting to think about, like what the moon looked

465
00:22:56,680 --> 00:22:59,680
Speaker 2: like to dinosaurs. Because while we think about maybe things

466
00:22:59,680 --> 00:23:03,040
Speaker 2: out in deep space, other galaxies, whatever, changing over time,

467
00:23:03,320 --> 00:23:06,879
Speaker 2: the Moon is also not static, like it's been orbiting

468
00:23:06,880 --> 00:23:09,200
Speaker 2: the Earth for lots and lots of years, but its

469
00:23:09,320 --> 00:23:12,480
Speaker 2: orbit is actually changing every year by how much? So

470
00:23:12,520 --> 00:23:15,000
Speaker 2: the Moon is orbiting the Earth and its orbit gets

471
00:23:15,080 --> 00:23:18,680
Speaker 2: larger by a couple of centimeters every year. Now, I know, Kelly,

472
00:23:18,680 --> 00:23:20,760
Speaker 2: you're not good with units, but like if you open

473
00:23:20,800 --> 00:23:22,480
Speaker 2: your fingers, you know.

474
00:23:22,600 --> 00:23:23,879
Speaker 1: Uh huh, all right, I'm doing it.

475
00:23:23,880 --> 00:23:26,200
Speaker 2: It's like the height of a really thick pastrami sandwich

476
00:23:26,280 --> 00:23:30,119
Speaker 2: or something, you know, so like a foot Wow, I

477
00:23:30,200 --> 00:23:32,600
Speaker 2: want to eat a Stromi sandwich at your house sometimes.

478
00:23:33,080 --> 00:23:36,199
Speaker 1: Yeah, Yeahoatmith house, I believe it.

479
00:23:36,240 --> 00:23:38,679
Speaker 2: And some of Zach's homemade rye bred of it. So

480
00:23:38,720 --> 00:23:40,679
Speaker 2: you might imagine that like two and a half centimeters

481
00:23:40,720 --> 00:23:43,080
Speaker 2: a year doesn't sound like a lot, but we got

482
00:23:43,119 --> 00:23:45,000
Speaker 2: a lot of years here, right, Like the diners were

483
00:23:45,080 --> 00:23:48,600
Speaker 2: lived a long time ago, and one hundred million years

484
00:23:48,720 --> 00:23:53,320
Speaker 2: adds up to like two thousand, two hundred kilometers over

485
00:23:53,359 --> 00:23:56,960
Speaker 2: all that time. So the Moon is further away from

486
00:23:57,000 --> 00:24:00,720
Speaker 2: the Earth by twenty two hundred kilometers than it was

487
00:24:00,760 --> 00:24:02,399
Speaker 2: when the dinosaurs were looking up at it.

488
00:24:02,480 --> 00:24:04,560
Speaker 1: Oh my gosh, So what is the total distance? Like,

489
00:24:04,600 --> 00:24:06,160
Speaker 1: what is the percent difference?

490
00:24:06,400 --> 00:24:08,600
Speaker 2: Yeah, that's exactly the right question, right, it doesn't make

491
00:24:08,640 --> 00:24:11,280
Speaker 2: any difference at all. Because if your friend was right

492
00:24:11,320 --> 00:24:13,880
Speaker 2: next to you and then a moment later they're twenty

493
00:24:13,920 --> 00:24:16,160
Speaker 2: two hundred cilometers away, it's going to make a big difference.

494
00:24:16,560 --> 00:24:18,359
Speaker 2: But the moon is not right next to us, and

495
00:24:18,480 --> 00:24:20,920
Speaker 2: was never right next to us on these time scales.

496
00:24:21,240 --> 00:24:24,119
Speaker 2: Its current distance is like three hundred and eighty three

497
00:24:24,119 --> 00:24:29,000
Speaker 2: thousand kilometers, so we're talking about like two thousand kilometers

498
00:24:29,440 --> 00:24:31,800
Speaker 2: more than the dinosaurs used to see it. That's only

499
00:24:31,840 --> 00:24:33,200
Speaker 2: like a half a percent.

500
00:24:33,000 --> 00:24:36,359
Speaker 1: Difference, okay, And so like if I went back in

501
00:24:36,440 --> 00:24:39,000
Speaker 1: a time machine, I probably wouldn't be able to tell

502
00:24:39,040 --> 00:24:39,520
Speaker 1: the difference.

503
00:24:39,600 --> 00:24:40,800
Speaker 2: That's a great way to think about it. Like, if

504
00:24:40,840 --> 00:24:42,720
Speaker 2: you get a time machine, if somebody spins the dial

505
00:24:42,760 --> 00:24:45,000
Speaker 2: and sends you back to an arbitrary time, could you

506
00:24:45,119 --> 00:24:47,480
Speaker 2: use the night sky to figure out like when it was,

507
00:24:47,520 --> 00:24:49,880
Speaker 2: would you notice any difference? So if you went back

508
00:24:49,920 --> 00:24:52,880
Speaker 2: to like the Cretaceous period sometime in the middle of that,

509
00:24:53,320 --> 00:24:55,399
Speaker 2: then you look at the night sky, you would notice

510
00:24:55,400 --> 00:24:58,000
Speaker 2: the moon would be like one percent bigger and like

511
00:24:58,119 --> 00:25:01,879
Speaker 2: one percent brighter than it is today. And so unless

512
00:25:01,880 --> 00:25:05,000
Speaker 2: you're like extraordinarily sensitive to moonlight, you're like a werewolf

513
00:25:05,080 --> 00:25:08,080
Speaker 2: or something, then you probably wouldn't notice. But be careful

514
00:25:08,080 --> 00:25:10,040
Speaker 2: about sending your werewolves back in time.

515
00:25:10,280 --> 00:25:12,800
Speaker 1: Yeah, no, no, you shouldn't know. I'll be very careful.

516
00:25:13,480 --> 00:25:16,760
Speaker 2: And fiction writers out there, if you have time traveling werewolves,

517
00:25:16,760 --> 00:25:18,560
Speaker 2: I want you to include this detail. I mean we're

518
00:25:18,560 --> 00:25:26,840
Speaker 2: talking hard science fiction here, hard to read. Kelly. Somebody

519
00:25:26,880 --> 00:25:29,040
Speaker 2: out there is pouring their heart into a time traveling

520
00:25:29,040 --> 00:25:31,879
Speaker 2: werewolf novel and you just dissed it without even reading it.

521
00:25:32,600 --> 00:25:34,920
Speaker 1: I'm so sorry. I promise I'll have an open mind.

522
00:25:36,200 --> 00:25:37,400
Speaker 1: It might end up being great.

523
00:25:37,480 --> 00:25:40,439
Speaker 2: Please send us your fiction about time traveling werewolves. I

524
00:25:40,480 --> 00:25:42,720
Speaker 2: promise to read it with an open mind under a

525
00:25:42,800 --> 00:25:43,880
Speaker 2: very bright full moon.

526
00:25:44,200 --> 00:25:48,640
Speaker 1: That's right, that's right. Okay, I think we've said everything

527
00:25:48,680 --> 00:25:50,280
Speaker 1: that needs to be said about the moon, and then

528
00:25:50,320 --> 00:25:53,680
Speaker 1: maybe a lot more. How about constellations? Are they gonna

529
00:25:53,720 --> 00:25:56,320
Speaker 1: be the same? Is Orion's belt still going to be

530
00:25:56,359 --> 00:25:58,879
Speaker 1: there for our Cosmololosaurus to find?

531
00:25:59,240 --> 00:26:01,719
Speaker 2: So this is where a big change really happens. And

532
00:26:01,760 --> 00:26:04,280
Speaker 2: the short version is that the night sky could look

533
00:26:04,359 --> 00:26:08,639
Speaker 2: dramatically different to the dinosaurs than to us for a

534
00:26:08,640 --> 00:26:12,399
Speaker 2: few reasons. Number one is that stars are not infinitely old,

535
00:26:12,440 --> 00:26:15,320
Speaker 2: and they don't last for an infinite number of years. Remember,

536
00:26:15,440 --> 00:26:17,679
Speaker 2: stars form when you have like a big cloud of

537
00:26:17,800 --> 00:26:21,520
Speaker 2: gas and dust that's cold enough that gravity can like

538
00:26:21,640 --> 00:26:23,760
Speaker 2: pull on it. For gas that's too hot, the particles

539
00:26:23,760 --> 00:26:26,680
Speaker 2: are just moving too fast for gravity to like gather

540
00:26:26,760 --> 00:26:29,159
Speaker 2: it together into a star, and this can take a

541
00:26:29,160 --> 00:26:32,399
Speaker 2: long time. Remember, our star was only born four and

542
00:26:32,440 --> 00:26:34,800
Speaker 2: a half billion years ago, which means there were ten

543
00:26:34,840 --> 00:26:36,359
Speaker 2: billion years in the life of the universe, in like

544
00:26:36,480 --> 00:26:39,720
Speaker 2: nine billion years in the life of our galaxy before

545
00:26:39,840 --> 00:26:43,520
Speaker 2: our star even existed. Right, So stars are being born

546
00:26:43,720 --> 00:26:46,440
Speaker 2: all the time, and so some stars that we see

547
00:26:46,440 --> 00:26:51,040
Speaker 2: in the night sky didn't even exist when Tyrannosaurus Rex

548
00:26:51,119 --> 00:26:53,560
Speaker 2: was trying to invent a telescope that he could lift

549
00:26:53,560 --> 00:26:54,359
Speaker 2: to his eyeballs.

550
00:26:54,600 --> 00:26:57,120
Speaker 1: Wow, and we can age stars, so we can get

551
00:26:57,119 --> 00:26:59,680
Speaker 1: an estimate for how many didn't exist, Is that right?

552
00:26:59,760 --> 00:27:03,240
Speaker 2: Yeah, we can have an idea for how old stars

553
00:27:03,280 --> 00:27:06,399
Speaker 2: are because we have a model of star formation and

554
00:27:06,440 --> 00:27:09,359
Speaker 2: how stars burn, and as stars burn, they tend to

555
00:27:09,359 --> 00:27:13,080
Speaker 2: get like bigger and brighter, or there's some variation depending

556
00:27:13,080 --> 00:27:15,560
Speaker 2: on the initial clump of stuff they had. But there's

557
00:27:15,560 --> 00:27:17,879
Speaker 2: a whole deep knowledge now of like the life cycle

558
00:27:17,920 --> 00:27:20,480
Speaker 2: of stars, and so you can look at stars, and

559
00:27:20,520 --> 00:27:23,040
Speaker 2: you can look at stars nearby and understand how they

560
00:27:23,040 --> 00:27:25,320
Speaker 2: form together. We have a whole episode about how to

561
00:27:25,400 --> 00:27:28,520
Speaker 2: tell the age of stars. It's really a fascinating science.

562
00:27:28,880 --> 00:27:31,520
Speaker 2: Mostly you have to look at stars nearby and understand

563
00:27:31,680 --> 00:27:33,760
Speaker 2: how they all form together. But sometimes you can get

564
00:27:33,800 --> 00:27:36,120
Speaker 2: clues from an individual star. But you know, to take

565
00:27:36,160 --> 00:27:39,880
Speaker 2: a particular example, the Pliades, which are a famous constellation.

566
00:27:40,280 --> 00:27:44,400
Speaker 2: They're only like thirteen million years old, and so we're

567
00:27:44,400 --> 00:27:47,240
Speaker 2: looking up at the night sky, we're seeing that constellation.

568
00:27:47,400 --> 00:27:51,480
Speaker 2: It appears in like you know, ancient astronomical texts. People

569
00:27:51,520 --> 00:27:55,240
Speaker 2: have seen these. You can even find like neolithic records

570
00:27:55,400 --> 00:27:59,639
Speaker 2: of this constellation from like Bronze Age shields where they

571
00:27:59,680 --> 00:28:02,280
Speaker 2: have like hammered the night sky in a pattern onto

572
00:28:02,280 --> 00:28:04,320
Speaker 2: the shield and you can see the Pliades on it.

573
00:28:04,320 --> 00:28:07,800
Speaker 2: It's pretty awesome. So humans have always seen this constellation,

574
00:28:08,080 --> 00:28:11,080
Speaker 2: but dinosaurs never did. It just hadn't come out yet.

575
00:28:11,160 --> 00:28:11,359
Speaker 3: You know.

576
00:28:11,400 --> 00:28:13,840
Speaker 2: It's sort of like asking if dinosaurs have seen the

577
00:28:13,880 --> 00:28:14,879
Speaker 2: Star Wars movies.

578
00:28:15,000 --> 00:28:18,440
Speaker 1: You know, yet one more reason why it's good to

579
00:28:18,480 --> 00:28:19,320
Speaker 1: not be a dinosaur.

580
00:28:20,760 --> 00:28:23,000
Speaker 2: Although Star Wars happened a long long time ago, so

581
00:28:23,119 --> 00:28:25,920
Speaker 2: it might have been like actually occurring while the dinosaurs

582
00:28:25,920 --> 00:28:27,879
Speaker 2: were here. It just took a long time for the

583
00:28:27,920 --> 00:28:31,520
Speaker 2: movies to get here from that galaxy far far away.

584
00:28:33,760 --> 00:28:34,600
Speaker 1: An excellent point.

585
00:28:35,440 --> 00:28:38,320
Speaker 2: And you know, stars also die. We see supernova, which

586
00:28:38,320 --> 00:28:40,680
Speaker 2: are the endpoint of stars, stars that have burned for

587
00:28:40,760 --> 00:28:43,240
Speaker 2: so long that they've basically turned all of their fuel

588
00:28:43,360 --> 00:28:46,960
Speaker 2: into ash. You know, like our star can burn hydrogen

589
00:28:47,240 --> 00:28:50,280
Speaker 2: and it creates helium, but it can't burn that helium,

590
00:28:50,440 --> 00:28:52,600
Speaker 2: so the helium falls to the center of the star

591
00:28:52,800 --> 00:28:55,280
Speaker 2: and basically tries to put the star out. So that's

592
00:28:55,280 --> 00:28:57,360
Speaker 2: why our star then starts to burn on the outer

593
00:28:57,520 --> 00:29:00,160
Speaker 2: layers where there's still hydrogen, and it puffs up and

594
00:29:00,200 --> 00:29:02,560
Speaker 2: gets big. And all stars will do this, and eventually

595
00:29:02,760 --> 00:29:05,480
Speaker 2: they'll burn through all of the gas that they can burn,

596
00:29:05,560 --> 00:29:08,080
Speaker 2: and there be so much gravity that they collapse in

597
00:29:08,120 --> 00:29:12,560
Speaker 2: a huge gravitational implosion, which then bounces back into an explosion,

598
00:29:12,880 --> 00:29:15,360
Speaker 2: and you get these really dramatic events in the sky.

599
00:29:15,480 --> 00:29:18,200
Speaker 2: We call them supernova. And what's left is not a star.

600
00:29:18,440 --> 00:29:20,880
Speaker 2: We can actually look back in history and see records

601
00:29:20,880 --> 00:29:24,120
Speaker 2: of these things dating back to like a thousand years ago.

602
00:29:24,560 --> 00:29:28,800
Speaker 2: There was a huge supernova in ten fifty four that

603
00:29:28,880 --> 00:29:31,360
Speaker 2: the Chinese recorded, and like, this must have been a

604
00:29:31,440 --> 00:29:34,040
Speaker 2: very dramatic event. It lasted for a few months in

605
00:29:34,080 --> 00:29:38,160
Speaker 2: their sky, this sudden appearance of something very very bright.

606
00:29:38,480 --> 00:29:41,120
Speaker 2: They noted it as a guest star. And when we

607
00:29:41,160 --> 00:29:42,800
Speaker 2: look up at the night sky in the same spot,

608
00:29:42,840 --> 00:29:45,800
Speaker 2: we see a nebula, which is a huge spray of

609
00:29:45,880 --> 00:29:49,880
Speaker 2: material that erupted from that supernova. So that's pretty awesome. Actually,

610
00:29:49,920 --> 00:29:53,000
Speaker 2: because we have like a thousand years of observations of

611
00:29:53,040 --> 00:29:56,000
Speaker 2: this thing, we can see it exploding sort of over time.

612
00:29:56,240 --> 00:29:58,920
Speaker 2: But you know, the star that was there is now gone,

613
00:29:59,280 --> 00:30:01,800
Speaker 2: and so if you look back million years ago, you

614
00:30:01,800 --> 00:30:03,800
Speaker 2: would have seen that star, and today that star is

615
00:30:03,840 --> 00:30:07,000
Speaker 2: no longer there. So the night sky is definitely changing

616
00:30:07,480 --> 00:30:09,719
Speaker 2: on the thousand or million year timeline.

617
00:30:09,800 --> 00:30:15,520
Speaker 1: Okay, so the dinosaurs both saw stars that we never

618
00:30:15,600 --> 00:30:18,480
Speaker 1: got to see and don't even know existed because supernovas

619
00:30:18,480 --> 00:30:22,160
Speaker 1: don't leave signatures for quite for millions of years, and

620
00:30:22,560 --> 00:30:24,440
Speaker 1: we see some stars that they don't see, So do

621
00:30:24,480 --> 00:30:26,760
Speaker 1: we have a general like, is it like about ten

622
00:30:26,800 --> 00:30:29,000
Speaker 1: percent of the visible stars different now or is it

623
00:30:29,200 --> 00:30:32,120
Speaker 1: just no impossible to get a number like that.

624
00:30:32,120 --> 00:30:34,280
Speaker 2: That's a great question. I don't have a number, but

625
00:30:34,320 --> 00:30:35,880
Speaker 2: we do have a sort of a sense of it

626
00:30:36,120 --> 00:30:38,240
Speaker 2: by thinking about the kind of stars that are out

627
00:30:38,240 --> 00:30:41,000
Speaker 2: there in the universe. Like in our galaxy, most of

628
00:30:41,040 --> 00:30:44,959
Speaker 2: the stars are red dwarfs. These are smaller, cooler stars

629
00:30:45,000 --> 00:30:48,000
Speaker 2: than ours, and they also last a lot longer. Our

630
00:30:48,040 --> 00:30:51,120
Speaker 2: star will burn for ten billion years, these red dwarves

631
00:30:51,160 --> 00:30:54,560
Speaker 2: will burn for much much longer, sometimes one hundred billion

632
00:30:54,640 --> 00:30:56,960
Speaker 2: years for example. So we think the red dwarfs that

633
00:30:56,960 --> 00:30:59,200
Speaker 2: are out there that we're seeing will last a long time,

634
00:30:59,240 --> 00:31:00,880
Speaker 2: and any red dwarfs that exists at the time of

635
00:31:00,880 --> 00:31:04,000
Speaker 2: the dinosaurs probably also exist. But the flip side of

636
00:31:04,000 --> 00:31:05,840
Speaker 2: that is when you look for the night sky, you

637
00:31:05,880 --> 00:31:09,000
Speaker 2: don't see any red dwarfs because even though they're the

638
00:31:09,040 --> 00:31:12,080
Speaker 2: most common star in the galaxy, they're so dim that

639
00:31:12,120 --> 00:31:14,480
Speaker 2: you really can't see any of them with the naked eye.

640
00:31:14,800 --> 00:31:16,920
Speaker 2: So that means that the stars we're seeing are the

641
00:31:16,960 --> 00:31:20,240
Speaker 2: brightest stars, which are the ones that are shortest lived,

642
00:31:20,360 --> 00:31:22,479
Speaker 2: and so like the typical life cycle of these stars

643
00:31:22,560 --> 00:31:26,400
Speaker 2: is much much shorter, though we're still talking typically hundreds

644
00:31:26,440 --> 00:31:29,120
Speaker 2: of millions of years or billions of years. And so

645
00:31:29,160 --> 00:31:31,840
Speaker 2: you know, of the nine thousand stars that we can see,

646
00:31:32,000 --> 00:31:34,160
Speaker 2: I'd be surprised if it was more than ten percent

647
00:31:34,480 --> 00:31:37,400
Speaker 2: that had burned out or been born in the time

648
00:31:37,560 --> 00:31:38,520
Speaker 2: since the dinosaurs.

649
00:31:38,560 --> 00:31:40,080
Speaker 1: Okay, so now we have a good sense for how

650
00:31:40,080 --> 00:31:43,680
Speaker 1: many of the stars both the dinosaurs and us got

651
00:31:43,680 --> 00:31:46,200
Speaker 1: to see, and when we get back from a break,

652
00:31:46,240 --> 00:31:52,719
Speaker 1: we'll talk about whether or not they're in the same spots.

653
00:32:01,680 --> 00:32:05,760
Speaker 1: All right, So you told us that the dinosaurs saw

654
00:32:05,840 --> 00:32:08,040
Speaker 1: some stars that we didn't get to see, and that

655
00:32:08,080 --> 00:32:10,760
Speaker 1: we see some stars that the dinosaurs didn't get to see.

656
00:32:11,400 --> 00:32:14,600
Speaker 1: Are the stars that sort of overlap in that ven diagram?

657
00:32:14,760 --> 00:32:16,080
Speaker 1: Are they in the same spots?

658
00:32:16,200 --> 00:32:19,160
Speaker 2: So the short answer is that they're not. Right. Stars

659
00:32:19,200 --> 00:32:21,960
Speaker 2: in the galaxy are not static. It's not like they're

660
00:32:22,000 --> 00:32:26,080
Speaker 2: all in the same place. Remember that the galaxy is rotating,

661
00:32:26,240 --> 00:32:29,200
Speaker 2: and that stars are moving through the galaxy, but not

662
00:32:29,400 --> 00:32:31,720
Speaker 2: all together. It's not like we're all in a merry

663
00:32:31,720 --> 00:32:34,240
Speaker 2: go round and everybody's picked their horse and they're going

664
00:32:34,320 --> 00:32:36,240
Speaker 2: up and down and they're just in the same place.

665
00:32:36,400 --> 00:32:39,560
Speaker 2: It's more like a crazy traffic circle in Europe where

666
00:32:39,560 --> 00:32:42,160
Speaker 2: everybody's driving at different speed, and some stars are like

667
00:32:42,400 --> 00:32:44,920
Speaker 2: weaving through other stars, and some stars are going in

668
00:32:44,920 --> 00:32:47,640
Speaker 2: the wrong direction, and so it's a lot more chaotic

669
00:32:47,680 --> 00:32:49,920
Speaker 2: than you might imagine. And over the timescale of like

670
00:32:50,040 --> 00:32:52,959
Speaker 2: hundreds of millions of years, a lot of these stars

671
00:32:53,040 --> 00:32:55,959
Speaker 2: move relative to Earth, and so we will not see

672
00:32:56,000 --> 00:32:57,440
Speaker 2: the same picture of the sky.

673
00:32:57,560 --> 00:32:57,840
Speaker 5: All right.

674
00:32:57,880 --> 00:33:00,680
Speaker 1: So, first of all, that sounds awful, not like those

675
00:33:00,680 --> 00:33:03,680
Speaker 1: traffic circles. One bit. It sounds very chaotic, and they're

676
00:33:03,680 --> 00:33:05,600
Speaker 1: probably running into each other. And it's amazing that we

677
00:33:05,640 --> 00:33:07,760
Speaker 1: can plot the paths of any of these. So how

678
00:33:07,880 --> 00:33:10,479
Speaker 1: much have things moved since the dinosaurs were around?

679
00:33:10,680 --> 00:33:12,800
Speaker 2: Yeah, maybe instead of traffic circle, we should say like

680
00:33:12,880 --> 00:33:15,400
Speaker 2: mumper cars. It's really much more dramatic than a typical

681
00:33:15,480 --> 00:33:18,880
Speaker 2: traffic circle where we hope nobody is colliding with each other. Well,

682
00:33:18,880 --> 00:33:21,720
Speaker 2: there's a big variation in the speeds of these stars.

683
00:33:21,840 --> 00:33:24,800
Speaker 2: The typical speed of stars relative to the Earth, it

684
00:33:24,880 --> 00:33:28,240
Speaker 2: can be like ten or twenty kilometers per second, but

685
00:33:28,360 --> 00:33:31,400
Speaker 2: some of them are super duper fast. There's some stars

686
00:33:31,440 --> 00:33:34,200
Speaker 2: they call like hypervelocity stars that can move up to

687
00:33:34,280 --> 00:33:37,880
Speaker 2: like one hundred kilometers per second, faster than like the

688
00:33:37,960 --> 00:33:40,800
Speaker 2: typical speed in the Milky Way. These are stars that

689
00:33:40,840 --> 00:33:44,200
Speaker 2: have like had some gravitational event happened to them. Maybe

690
00:33:44,200 --> 00:33:46,720
Speaker 2: they whizzed through the center of the galaxy and got

691
00:33:46,760 --> 00:33:49,760
Speaker 2: accelerated by the black hole or had some near approach

692
00:33:49,840 --> 00:33:53,280
Speaker 2: to something else which really changed their direction, and so

693
00:33:53,400 --> 00:33:56,480
Speaker 2: like a hypervelocity star would like move across the sky

694
00:33:56,840 --> 00:33:59,960
Speaker 2: very quickly on the timescale of us in the dinosaur.

695
00:34:00,320 --> 00:34:02,680
Speaker 2: But in general, things tend to move sort of in blobs.

696
00:34:02,960 --> 00:34:06,200
Speaker 2: Like stars are born not individually. Stars tend to be

697
00:34:06,200 --> 00:34:09,080
Speaker 2: born together. You have like a star forming region. We

698
00:34:09,160 --> 00:34:12,200
Speaker 2: call these stellar nurseries where a bunch of stars were

699
00:34:12,200 --> 00:34:15,240
Speaker 2: all made at once. We painted this picture of stars

700
00:34:15,320 --> 00:34:18,560
Speaker 2: forming from gas clouds collapsing. But it's not like one

701
00:34:18,560 --> 00:34:21,880
Speaker 2: gas cloud equals one star or one solar system. You

702
00:34:21,960 --> 00:34:24,440
Speaker 2: tend to have like a huge gas cloud and it

703
00:34:24,480 --> 00:34:28,360
Speaker 2: collapses into multiple stars all at once. So you have

704
00:34:28,400 --> 00:34:31,480
Speaker 2: a bunch of stars with like a common origin, and

705
00:34:31,520 --> 00:34:34,359
Speaker 2: then they tend to have like common kinematics. Right, they

706
00:34:34,440 --> 00:34:37,240
Speaker 2: move sort of as a group for a little while

707
00:34:37,520 --> 00:34:40,720
Speaker 2: until they dissipate and get absorbed into the general flow

708
00:34:40,920 --> 00:34:42,759
Speaker 2: of the milky Way. So instead of thinking of the

709
00:34:42,760 --> 00:34:44,920
Speaker 2: Milky Way as like a merry go round, think of

710
00:34:44,920 --> 00:34:47,560
Speaker 2: it like a bunch of different gangs on the bumper

711
00:34:47,600 --> 00:34:50,600
Speaker 2: car floor, like all moving together, competing with each other.

712
00:34:51,280 --> 00:34:55,400
Speaker 1: So this might be a silly question. Are constellations usually

713
00:34:55,440 --> 00:34:59,239
Speaker 1: from the same nursery or are constellations made up of

714
00:34:59,280 --> 00:35:01,440
Speaker 1: stars that are much farther apart than that, but our

715
00:35:01,480 --> 00:35:03,520
Speaker 1: brain just makes patterns with them anyway, Oh, it's.

716
00:35:03,440 --> 00:35:06,000
Speaker 2: A great question. The short answer is that you're not

717
00:35:06,040 --> 00:35:09,880
Speaker 2: guaranteed at all that constellations in the sky have stars

718
00:35:09,880 --> 00:35:11,799
Speaker 2: that are near each other, right, They just happen to

719
00:35:11,960 --> 00:35:15,000
Speaker 2: line up from our perspective, and so they might not

720
00:35:15,120 --> 00:35:17,240
Speaker 2: be near each other at all. There could be one

721
00:35:17,320 --> 00:35:19,680
Speaker 2: that's fairly dim but close to us, and we can

722
00:35:19,680 --> 00:35:22,320
Speaker 2: see it in another one that's super bright but far away,

723
00:35:22,520 --> 00:35:24,799
Speaker 2: and so it lines up in the sky near us.

724
00:35:24,840 --> 00:35:27,960
Speaker 2: And I always felt like constellations, I don't understand why

725
00:35:28,000 --> 00:35:31,240
Speaker 2: they're typically taught in the beginning of like astronomy courses,

726
00:35:31,320 --> 00:35:34,840
Speaker 2: because there's nothing to them, right. It's like casting a

727
00:35:34,880 --> 00:35:37,200
Speaker 2: bunch of dye on the floor and saying, like, let's

728
00:35:37,239 --> 00:35:40,040
Speaker 2: learn about the universe. From these random numbers that really

729
00:35:40,120 --> 00:35:42,759
Speaker 2: tells you nothing about what's happening in the universe. I mean,

730
00:35:42,760 --> 00:35:45,120
Speaker 2: I guess it's like accessible and that's how people like

731
00:35:45,280 --> 00:35:48,600
Speaker 2: latch onto astronomy by looking at the stars. But I

732
00:35:48,600 --> 00:35:50,680
Speaker 2: feel like there's so much actual science you can teach

733
00:35:50,680 --> 00:35:53,560
Speaker 2: people instead of like basically astrology. But some of the

734
00:35:53,600 --> 00:35:57,000
Speaker 2: constellations are moving together, like the Big Dipper, the Big Dipper,

735
00:35:57,080 --> 00:35:59,880
Speaker 2: most of those stars were formed about the same time,

736
00:36:00,480 --> 00:36:02,960
Speaker 2: and they're in a group that are all moving together.

737
00:36:03,280 --> 00:36:06,319
Speaker 2: And it's actually a very big, very fast moving group

738
00:36:06,360 --> 00:36:09,040
Speaker 2: of stars that are all sort of like running together

739
00:36:09,200 --> 00:36:10,280
Speaker 2: across the universe.

740
00:36:10,440 --> 00:36:13,360
Speaker 1: Are they all moving at hypervelocity.

741
00:36:13,239 --> 00:36:17,160
Speaker 2: Not quite at hypervelocity, but definitely tens of kilometers. And

742
00:36:17,200 --> 00:36:20,280
Speaker 2: it's one of the largest and closest of these kinematic groups.

743
00:36:20,320 --> 00:36:22,400
Speaker 2: They call it the ursa major moving group, so it

744
00:36:22,440 --> 00:36:25,920
Speaker 2: includes the Big Dipper, and it's moving so fast that

745
00:36:25,960 --> 00:36:28,560
Speaker 2: if you rewound the clocklin even just one hundred and

746
00:36:28,600 --> 00:36:31,640
Speaker 2: fifty thousand years, you would not see the Big Dipper

747
00:36:31,640 --> 00:36:32,200
Speaker 2: in the sky.

748
00:36:32,480 --> 00:36:32,560
Speaker 3: No.

749
00:36:33,040 --> 00:36:34,600
Speaker 2: Yeah, it's a good thing to check for when you

750
00:36:34,680 --> 00:36:37,800
Speaker 2: get out of your time machine with your werewolves. Yeah,

751
00:36:39,080 --> 00:36:41,520
Speaker 2: or fine, if you don't like traveling with a werewolfs

752
00:36:41,560 --> 00:36:43,320
Speaker 2: leave it at home, but still look up at the

753
00:36:43,400 --> 00:36:45,560
Speaker 2: night sky and check for the Big Dipper when you

754
00:36:45,600 --> 00:36:46,800
Speaker 2: get out of your time machine.

755
00:36:46,880 --> 00:36:49,319
Speaker 1: I feel like this is almost like rattling to me.

756
00:36:49,400 --> 00:36:51,319
Speaker 1: You know, one of the first things I learned about

757
00:36:51,320 --> 00:36:53,279
Speaker 1: the night sky was the Big Dipper, just like the

758
00:36:53,360 --> 00:36:57,040
Speaker 1: idea that it wasn't there for the dinosaurs is it

759
00:36:57,120 --> 00:36:59,000
Speaker 1: makes sense, but I guess I'd never thought of that.

760
00:36:59,000 --> 00:37:02,359
Speaker 2: That's OK, yeah, and it means that they definitely saw

761
00:37:02,520 --> 00:37:05,680
Speaker 2: other constellations. Like you would not recognize the night sky

762
00:37:06,000 --> 00:37:09,120
Speaker 2: from the dinosaurs times because it's dynamic. We tend to

763
00:37:09,120 --> 00:37:10,880
Speaker 2: think of it as static. And I look up in

764
00:37:10,920 --> 00:37:12,680
Speaker 2: the night sky and I wonder if you know ancient

765
00:37:12,719 --> 00:37:15,839
Speaker 2: astronomers or chro magnet man looked up the night sky

766
00:37:15,880 --> 00:37:18,200
Speaker 2: and saw the same thing. And most likely they did.

767
00:37:18,560 --> 00:37:20,920
Speaker 2: But you go far enough back in time, in deep

768
00:37:21,040 --> 00:37:23,960
Speaker 2: cosmic time, then you'll notice that these things are swimming.

769
00:37:24,080 --> 00:37:26,319
Speaker 2: I would love to see like a time lapse of

770
00:37:26,400 --> 00:37:30,000
Speaker 2: the sky dating back like one hundred and fifty million years,

771
00:37:30,200 --> 00:37:33,640
Speaker 2: because you would see things move right, and they are moving,

772
00:37:33,680 --> 00:37:36,360
Speaker 2: it's just moving so slowly that from our perspective, it

773
00:37:36,400 --> 00:37:38,440
Speaker 2: looks like nothing's happening. It's like checking in on the

774
00:37:38,440 --> 00:37:40,960
Speaker 2: Grand Canyon every couple of years being like, oh, this

775
00:37:41,040 --> 00:37:44,680
Speaker 2: thing's not changing, whereas we know right that over time,

776
00:37:44,840 --> 00:37:47,839
Speaker 2: of course, it's changing and growing, and a time lapse

777
00:37:47,840 --> 00:37:50,799
Speaker 2: would reveal it to be a dynamical system in progress.

778
00:37:51,120 --> 00:37:53,839
Speaker 2: Same thing with the stars. They're up there swirling around

779
00:37:53,840 --> 00:37:56,520
Speaker 2: and changing and swinging around each other, and the night

780
00:37:56,600 --> 00:37:57,920
Speaker 2: sky is definitely in motion.

781
00:37:58,360 --> 00:38:01,719
Speaker 1: It would be so cool to see that timeline. That's

782
00:38:01,760 --> 00:38:04,840
Speaker 1: never going to happen unless you get both the werewolf

783
00:38:04,880 --> 00:38:06,240
Speaker 1: at a time machine.

784
00:38:05,920 --> 00:38:08,879
Speaker 2: Or and there are other effects going on. It's not

785
00:38:09,080 --> 00:38:11,879
Speaker 2: just the night sky is changing around us that these

786
00:38:11,920 --> 00:38:16,480
Speaker 2: stars are moving relative to us. We're also moving relative

787
00:38:16,600 --> 00:38:17,560
Speaker 2: to the galaxy.

788
00:38:17,719 --> 00:38:18,600
Speaker 1: We're not in the center.

789
00:38:18,800 --> 00:38:20,720
Speaker 2: We're not in the center of the galaxy for sure.

790
00:38:20,880 --> 00:38:23,440
Speaker 2: Right we're like halfway out from the center. And you

791
00:38:23,440 --> 00:38:25,480
Speaker 2: should be glad we're not out in the center, because

792
00:38:25,520 --> 00:38:28,160
Speaker 2: it's crazy in there. You know, it's like very dense

793
00:38:28,200 --> 00:38:30,719
Speaker 2: with stars and radiation, and our kind of life could

794
00:38:30,760 --> 00:38:33,360
Speaker 2: not survive. We're safe out in the suburbs of the galaxy,

795
00:38:33,400 --> 00:38:35,360
Speaker 2: not so far out in like the exurbs with the

796
00:38:35,400 --> 00:38:37,600
Speaker 2: star density is very very low. We're like, you know,

797
00:38:37,680 --> 00:38:40,279
Speaker 2: halfway out from the center of the galaxy. But we

798
00:38:40,360 --> 00:38:42,240
Speaker 2: go around the galaxy and it takes like two hundred

799
00:38:42,239 --> 00:38:45,040
Speaker 2: and fifty million years for the galaxy to rotate. But

800
00:38:45,160 --> 00:38:49,000
Speaker 2: while that's happening, the Sun does this really interesting and

801
00:38:49,080 --> 00:38:52,080
Speaker 2: weird thing is that it goes up and down. So

802
00:38:52,160 --> 00:38:54,600
Speaker 2: imagine like the plane of the galaxy, the Milky Way

803
00:38:54,680 --> 00:38:57,120
Speaker 2: is like flat disk. The Sun is going through that

804
00:38:57,200 --> 00:38:59,399
Speaker 2: disk and then back out the bottom and then coming

805
00:38:59,440 --> 00:39:01,879
Speaker 2: back up again and through the top of it. It's

806
00:39:01,880 --> 00:39:03,640
Speaker 2: going like up and down in a sort of a

807
00:39:03,719 --> 00:39:06,440
Speaker 2: cyan wave through the disk of the galaxy.

808
00:39:06,600 --> 00:39:09,960
Speaker 1: The solar like the galaxies are dancing. Why does it

809
00:39:10,000 --> 00:39:10,279
Speaker 1: do that.

810
00:39:10,560 --> 00:39:12,600
Speaker 2: It's sort of like on the Merry Go Round where

811
00:39:12,640 --> 00:39:15,239
Speaker 2: your horse goes up and down and it's just oscillating.

812
00:39:15,320 --> 00:39:17,719
Speaker 2: Like most of the gravity is at the center of

813
00:39:17,760 --> 00:39:20,759
Speaker 2: the galaxy. And from this perspective, we mean like the

814
00:39:20,800 --> 00:39:24,040
Speaker 2: plane of the galaxy, and so it's attracted to the

815
00:39:24,040 --> 00:39:26,360
Speaker 2: plane of the galaxy, which slurps it in it applies

816
00:39:26,400 --> 00:39:28,359
Speaker 2: basically a force to it. But then when it gets

817
00:39:28,400 --> 00:39:30,720
Speaker 2: to the plane of the galaxy, it's moving fast because

818
00:39:30,719 --> 00:39:33,920
Speaker 2: it's been tugged on by that gravity and it passes

819
00:39:33,960 --> 00:39:36,920
Speaker 2: through it, and then the galaxy slows it down as

820
00:39:36,920 --> 00:39:38,799
Speaker 2: it goes through the bottom and turns it around and

821
00:39:38,840 --> 00:39:41,319
Speaker 2: pulls it back. So it's basically like a pendulum. The

822
00:39:41,400 --> 00:39:44,799
Speaker 2: Sun is oscillating around the center of the galaxy over

823
00:39:44,920 --> 00:39:47,120
Speaker 2: like a thirty million year cycle.

824
00:39:47,400 --> 00:39:49,560
Speaker 1: So does that mean that if you look out that

825
00:39:49,719 --> 00:39:52,240
Speaker 1: like for the dinosaurs, some of the stars were higher

826
00:39:52,239 --> 00:39:54,400
Speaker 1: in the sky and then later they're lower in the

827
00:39:54,400 --> 00:39:57,520
Speaker 1: sky or no, because the Milky Way moves all as

828
00:39:57,680 --> 00:40:00,399
Speaker 1: one and it's the rest of the stuff that moving

829
00:40:00,560 --> 00:40:01,359
Speaker 1: relative to us.

830
00:40:01,719 --> 00:40:03,840
Speaker 2: Yeah, it's a great question. It's not that the Milky

831
00:40:03,880 --> 00:40:05,520
Speaker 2: Way moves all at one, right, It is all these

832
00:40:05,560 --> 00:40:08,560
Speaker 2: blobs of kinematic groups that are moving, and the Sun

833
00:40:08,640 --> 00:40:11,440
Speaker 2: is basically moving through it. And so as we go down,

834
00:40:11,719 --> 00:40:13,680
Speaker 2: all the stars that are near us change and then

835
00:40:13,719 --> 00:40:16,120
Speaker 2: we come back up. Some of those are oscillating on

836
00:40:16,280 --> 00:40:19,279
Speaker 2: different cycles than hours, So like every thirty million years,

837
00:40:19,320 --> 00:40:21,800
Speaker 2: you like go into water and come back up, things

838
00:40:21,840 --> 00:40:24,480
Speaker 2: can really have changed. In the meantime. We're not the

839
00:40:24,520 --> 00:40:27,200
Speaker 2: only star that does this kind of oscillation, so there's

840
00:40:27,200 --> 00:40:29,200
Speaker 2: a sort of a lot of change in our galactic

841
00:40:29,239 --> 00:40:31,600
Speaker 2: neighborhood on a million year timescale.

842
00:40:31,719 --> 00:40:34,080
Speaker 1: I feel like I've never wanted a time machine more

843
00:40:34,360 --> 00:40:37,719
Speaker 1: than during this conversation. It would be so cool to

844
00:40:37,760 --> 00:40:38,440
Speaker 1: see this stuff.

845
00:40:38,560 --> 00:40:41,440
Speaker 2: There's another really interesting effect just from the rotation of

846
00:40:41,520 --> 00:40:44,160
Speaker 2: the galaxy. Like you look at the galaxy like Andromeda

847
00:40:44,320 --> 00:40:47,279
Speaker 2: or most galaxies, you see that they have these arms. Right,

848
00:40:47,480 --> 00:40:49,960
Speaker 2: there's the central bar and then these arms where the

849
00:40:49,960 --> 00:40:52,440
Speaker 2: stars are denser than other things. And we know that

850
00:40:52,560 --> 00:40:55,759
Speaker 2: galaxies are rotating. I think that most people imagine those

851
00:40:56,000 --> 00:40:58,919
Speaker 2: arms to be like physical structures. They have a bunch

852
00:40:58,920 --> 00:41:01,360
Speaker 2: of stars in them, and as it rotates, those stars

853
00:41:01,400 --> 00:41:04,040
Speaker 2: all move together the way like if you spin your

854
00:41:04,120 --> 00:41:06,839
Speaker 2: arm around your body, all the cells in your arm

855
00:41:07,000 --> 00:41:09,920
Speaker 2: move together, right, your arm stays together. But the galaxy's

856
00:41:10,040 --> 00:41:12,719
Speaker 2: arms are not like that at all. Those arms are

857
00:41:12,719 --> 00:41:16,520
Speaker 2: not physical structures. They're density waves. They're more like if

858
00:41:16,560 --> 00:41:18,239
Speaker 2: you go to a football game and people do the

859
00:41:18,280 --> 00:41:21,759
Speaker 2: wave right, the wave moves through the crowd, but the

860
00:41:21,800 --> 00:41:25,239
Speaker 2: crowd doesn't move right. It's those people's arms going up

861
00:41:25,280 --> 00:41:27,640
Speaker 2: and down that creates this impression of a wave.

862
00:41:27,760 --> 00:41:29,960
Speaker 1: And there's always those people that don't keep up.

863
00:41:30,280 --> 00:41:33,640
Speaker 2: Exactly and that's what's happening in the galaxy. It's not

864
00:41:33,760 --> 00:41:37,000
Speaker 2: that the stars in those arms are all moving together. Instead,

865
00:41:37,040 --> 00:41:39,839
Speaker 2: there's a density wave with things pulled together, and then

866
00:41:39,840 --> 00:41:43,719
Speaker 2: that dense blob moves through the galaxy. So it's sort

867
00:41:43,719 --> 00:41:45,480
Speaker 2: of like a traffic pattern, right, you know, like when

868
00:41:45,480 --> 00:41:47,560
Speaker 2: you're driving on the freeway and somebody slams on their

869
00:41:47,600 --> 00:41:49,680
Speaker 2: brakes and then the cars bunch up and then they

870
00:41:49,719 --> 00:41:51,839
Speaker 2: speed up, but the cars that were behind them end

871
00:41:51,920 --> 00:41:55,080
Speaker 2: up bunching up at the same place. Right. So stars

872
00:41:55,120 --> 00:41:58,160
Speaker 2: are moving through this density wave and then out of

873
00:41:58,200 --> 00:42:00,799
Speaker 2: the density wave on the other side, which means something

874
00:42:00,840 --> 00:42:03,960
Speaker 2: really interesting for star watching. It means that sometimes you're

875
00:42:03,960 --> 00:42:06,400
Speaker 2: in the arm, which means there are more stars near you,

876
00:42:06,600 --> 00:42:08,920
Speaker 2: and sometimes you're out of the arm, which means there

877
00:42:08,960 --> 00:42:11,080
Speaker 2: are fewer stars visible to you.

878
00:42:11,400 --> 00:42:14,120
Speaker 1: WHOA, Okay, So what kind of time skills are we

879
00:42:14,160 --> 00:42:15,520
Speaker 1: talking about? How long does it take to get in

880
00:42:15,600 --> 00:42:16,200
Speaker 1: or out of the arm.

881
00:42:16,280 --> 00:42:19,400
Speaker 2: So the Sun is actually moving through the galaxy like

882
00:42:19,560 --> 00:42:22,920
Speaker 2: twice as fast as the arm, so we like pass

883
00:42:23,000 --> 00:42:25,400
Speaker 2: through the arm and out the other side. So the

884
00:42:25,440 --> 00:42:28,799
Speaker 2: Sun is moving like twenty nine kilometers per second through

885
00:42:28,840 --> 00:42:31,759
Speaker 2: the galaxy and these density wave arms are moving like

886
00:42:31,840 --> 00:42:35,040
Speaker 2: seventeen kilometers per second, but they're pretty big, So we're

887
00:42:35,080 --> 00:42:38,439
Speaker 2: talking like tens of millions of years to go through

888
00:42:38,480 --> 00:42:41,680
Speaker 2: the density wave. It also means something really cool about

889
00:42:41,760 --> 00:42:45,399
Speaker 2: beyond the galaxy. Right, the galaxy rotates every two hundred

890
00:42:45,440 --> 00:42:48,279
Speaker 2: and fifty million years on average, and the dinosaurs lived,

891
00:42:48,440 --> 00:42:50,120
Speaker 2: you know, like one hundred and fifty to two hundred

892
00:42:50,160 --> 00:42:53,400
Speaker 2: million years ago. That means that the dinosaurs basically lived

893
00:42:53,520 --> 00:42:56,200
Speaker 2: on the other side of the galaxy, or like when

894
00:42:56,239 --> 00:42:59,560
Speaker 2: the galaxy was spun around halfway around, right.

895
00:42:59,560 --> 00:43:00,440
Speaker 8: I have to say.

896
00:43:02,239 --> 00:43:05,680
Speaker 2: And so even though we can't see beyond the galaxy

897
00:43:05,680 --> 00:43:09,440
Speaker 2: with the naked eye, our view of other galaxies has

898
00:43:09,560 --> 00:43:12,840
Speaker 2: changed completely in one hundred million years. We're like looking

899
00:43:12,840 --> 00:43:15,640
Speaker 2: at a completely different part of the universe. When we

900
00:43:15,680 --> 00:43:19,120
Speaker 2: look out from our galaxy is as big a difference

901
00:43:19,160 --> 00:43:21,600
Speaker 2: as like winter and summer galaxies. Right, you're just looking

902
00:43:21,640 --> 00:43:24,800
Speaker 2: at a completely different part of the sky. So dinosaur

903
00:43:24,800 --> 00:43:27,719
Speaker 2: has basically evolved on the other side of the galaxy.

904
00:43:27,920 --> 00:43:31,160
Speaker 2: They were never here, right, Those dinosaurs never existed in

905
00:43:31,200 --> 00:43:32,520
Speaker 2: this part of the galaxy.

906
00:43:32,640 --> 00:43:34,920
Speaker 1: I'll be honest. When we said we were going to

907
00:43:35,160 --> 00:43:37,520
Speaker 1: do this topic, I thought like maybe there'll be some

908
00:43:37,560 --> 00:43:40,680
Speaker 1: more stars or fewer stars, and maybe things have shifted around.

909
00:43:41,000 --> 00:43:43,120
Speaker 1: I did not expect the answer to be the sixth Street.

910
00:43:44,040 --> 00:43:46,120
Speaker 2: There's some other fun effects too that I want to

911
00:43:46,120 --> 00:43:48,840
Speaker 2: get into that the listeners talked about. Somebody mentioned the

912
00:43:48,920 --> 00:43:53,120
Speaker 2: expansion of the universe, right, because the universe is getting bigger,

913
00:43:53,239 --> 00:43:56,760
Speaker 2: and that expansion is happening faster and faster every year,

914
00:43:57,280 --> 00:44:00,520
Speaker 2: and so that's true that galaxies are getting fir away.

915
00:44:00,560 --> 00:44:03,160
Speaker 2: And again, we can't see galaxies with the naked eye,

916
00:44:03,200 --> 00:44:05,879
Speaker 2: and the dinosaurs definitely didn't have the technology. But it's

917
00:44:05,880 --> 00:44:09,360
Speaker 2: interesting to imagine, like, could those galaxies have been closer

918
00:44:09,640 --> 00:44:12,479
Speaker 2: during the dinosaurs times? Could maybe they have seen them

919
00:44:12,640 --> 00:44:15,360
Speaker 2: with the naked eye? Well, the answer is, unfortunately probably not.

920
00:44:15,640 --> 00:44:18,080
Speaker 2: The structure of the universe on a really really big

921
00:44:18,120 --> 00:44:21,080
Speaker 2: scale is dominated by dark energy, this thing tearing the

922
00:44:21,200 --> 00:44:24,799
Speaker 2: universe apart, making it expand. But the organization of our

923
00:44:24,840 --> 00:44:28,480
Speaker 2: galaxy and the neighboring galaxies altogether is mostly just dominated

924
00:44:28,480 --> 00:44:32,200
Speaker 2: by gravity. Like, dark energy is not powerful enough to

925
00:44:32,280 --> 00:44:35,359
Speaker 2: really affect the structure of our galaxy or of our

926
00:44:35,400 --> 00:44:40,319
Speaker 2: relationship with nearby galaxies, like Andromeda is headed towards us,

927
00:44:40,719 --> 00:44:44,440
Speaker 2: despite dark energy expanding the space between us, because gravity

928
00:44:44,480 --> 00:44:47,920
Speaker 2: on that scale is more powerful than dark energy. Shorter

929
00:44:48,040 --> 00:44:52,640
Speaker 2: distances like between galaxies, gravity dominates, and longer distances like

930
00:44:52,719 --> 00:44:56,759
Speaker 2: between clusters of galaxies, that's when dark energy really takes over.

931
00:44:56,920 --> 00:44:58,800
Speaker 2: The other issue is that like two hundred and fifty

932
00:44:58,800 --> 00:45:01,319
Speaker 2: million years sounds like a long time, but it's only

933
00:45:01,360 --> 00:45:04,799
Speaker 2: like two percent of the age of the universe, so

934
00:45:04,840 --> 00:45:07,879
Speaker 2: there hasn't really been time for dark energy to dramatically

935
00:45:08,000 --> 00:45:11,080
Speaker 2: change the arrangements of galaxies in that time.

936
00:45:11,360 --> 00:45:14,239
Speaker 1: Well, there's one difference in the night sky that I'm

937
00:45:14,320 --> 00:45:16,440
Speaker 1: sure the dinosaurs. I don't know how good or bad

938
00:45:16,480 --> 00:45:18,520
Speaker 1: their vision was, but I'm sure they didn't miss this.

939
00:45:19,760 --> 00:45:20,760
Speaker 1: How about that asteroid.

940
00:45:23,800 --> 00:45:27,520
Speaker 2: That asteroid probably was totally visible to the t rexes

941
00:45:27,560 --> 00:45:31,160
Speaker 2: and whoever else was around, And they're proto astronomers. We

942
00:45:31,239 --> 00:45:35,920
Speaker 2: imagine that asteroid was probably moving around thirty kilometers per second,

943
00:45:35,960 --> 00:45:38,480
Speaker 2: which means that if it's approaching the Earth, it gets

944
00:45:38,520 --> 00:45:43,000
Speaker 2: closer by like two point six million kilometers every single day.

945
00:45:43,520 --> 00:45:45,919
Speaker 2: And they've actually done a reconstruction to think like how

946
00:45:45,960 --> 00:45:48,480
Speaker 2: far away was it when it was visible? And they

947
00:45:48,520 --> 00:45:51,320
Speaker 2: think that probably it was visible to the naked eye

948
00:45:51,360 --> 00:45:54,759
Speaker 2: for like three days before it actually entered the atmosphere,

949
00:45:55,120 --> 00:45:58,279
Speaker 2: because it probably reflected enough sunlight to be visible in

950
00:45:58,320 --> 00:46:01,200
Speaker 2: the night sky. It's like, huh, what's that? And so

951
00:46:01,680 --> 00:46:04,000
Speaker 2: you know, if they've been paying attention, they had at

952
00:46:04,120 --> 00:46:06,080
Speaker 2: least three days to build their bunkers.

953
00:46:06,320 --> 00:46:08,560
Speaker 1: Oh boy, I don't think that's enough time.

954
00:46:08,600 --> 00:46:11,960
Speaker 2: It's detainly not enough time, which is why dinosaurs needed

955
00:46:11,960 --> 00:46:14,640
Speaker 2: to really fund their astronomy programs and think about this

956
00:46:14,680 --> 00:46:18,000
Speaker 2: stuff so they have like more warning before something hit them.

957
00:46:18,239 --> 00:46:19,760
Speaker 1: Absolutely, But you know that's.

958
00:46:19,640 --> 00:46:21,480
Speaker 2: A moral question, Like if you go back in time

959
00:46:21,520 --> 00:46:24,279
Speaker 2: in your time machine to the dinosaur time, should you

960
00:46:24,760 --> 00:46:27,840
Speaker 2: lobby dinosaur Congress to fund astronomy which might prevent the

961
00:46:27,840 --> 00:46:30,160
Speaker 2: evolution of mammals and you and your kids?

962
00:46:30,320 --> 00:46:34,040
Speaker 1: I think they might just eat that's my biologist perspective here.

963
00:46:34,160 --> 00:46:36,920
Speaker 2: Even if you come with valuable information, they're just going

964
00:46:36,960 --> 00:46:37,680
Speaker 2: to gobble you up.

965
00:46:37,840 --> 00:46:39,680
Speaker 1: Yeah, you know, I think probably that's how it would go.

966
00:46:40,040 --> 00:46:41,960
Speaker 2: I guess there's a good lesson there. You know, if

967
00:46:42,000 --> 00:46:45,879
Speaker 2: we get visitors from the future, you know, future reptiles

968
00:46:46,040 --> 00:46:48,520
Speaker 2: or whatever is going to replace humans when we kill ourselves,

969
00:46:48,560 --> 00:46:50,880
Speaker 2: we shouldn't just eat them. We should listen to them first,

970
00:46:50,920 --> 00:46:51,680
Speaker 2: that's what you're saying.

971
00:46:51,840 --> 00:46:53,120
Speaker 1: Yeah, don't eat the visitors.

972
00:46:53,160 --> 00:46:56,080
Speaker 2: That's right, and that's the lesson for your kids. You

973
00:46:56,080 --> 00:46:58,319
Speaker 2: know that we should fund astronomy today so that we

974
00:46:58,400 --> 00:47:01,080
Speaker 2: can be better prepared than the dinosaur were when they

975
00:47:01,120 --> 00:47:03,879
Speaker 2: looked up at their night sky. And also, don't eat

976
00:47:04,000 --> 00:47:05,799
Speaker 2: the future time traveling werewolves.

977
00:47:05,960 --> 00:47:09,040
Speaker 1: Oh my gosh. We covered a lot of ground today,

978
00:47:09,960 --> 00:47:11,560
Speaker 1: both fictional and otherwise.

979
00:47:11,800 --> 00:47:13,839
Speaker 2: So I think it's really fun to think about the

980
00:47:13,880 --> 00:47:17,200
Speaker 2: depth of the night sky and how it changes over time.

981
00:47:17,640 --> 00:47:21,240
Speaker 2: And it's sort of cool this coincidence that, like, astronomical

982
00:47:21,280 --> 00:47:23,800
Speaker 2: time scales are very very different from the time scales

983
00:47:23,840 --> 00:47:27,279
Speaker 2: of a human lifetime or even human history, but they

984
00:47:27,320 --> 00:47:30,480
Speaker 2: do kind of line up with archaeological time scales. Right

985
00:47:30,560 --> 00:47:33,480
Speaker 2: when we think about the dinosaurs one hundred two hundred

986
00:47:33,480 --> 00:47:36,680
Speaker 2: million years ago, that's long enough to really see a

987
00:47:36,800 --> 00:47:39,560
Speaker 2: change in our astronomical neighborhood.

988
00:47:39,640 --> 00:47:41,120
Speaker 1: Quite a big change.

989
00:47:41,160 --> 00:47:43,520
Speaker 2: Quite a big change indeed. All right, thanks very much

990
00:47:43,520 --> 00:47:46,480
Speaker 2: everybody for coming along on this tour of deep time

991
00:47:46,680 --> 00:47:50,040
Speaker 2: and this trip into our imagination for what dyn astronomers

992
00:47:50,160 --> 00:47:52,239
Speaker 2: might have seen. And thanks very much to Kelly for

993
00:47:52,320 --> 00:47:55,120
Speaker 2: going along and laughing at our time traveling were wolf jokes.

994
00:47:55,280 --> 00:47:58,480
Speaker 1: Thanks for having me. It was a blast as always, all.

995
00:47:58,520 --> 00:48:00,759
Speaker 2: Right everyone, Thanks for listening to and in next time,

996
00:48:08,760 --> 00:48:11,560
Speaker 2: thanks for listening and remember that Daniel and Jorge Explain

997
00:48:11,640 --> 00:48:15,640
Speaker 2: the Universe is a production of iHeartRadio. For more podcasts

998
00:48:15,640 --> 00:48:20,280
Speaker 2: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever

999
00:48:20,360 --> 00:48:22,080
Speaker 2: you listen to your favorite shows.