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Why are stars different colors? · Daniel and Kelly’s Extraordinary Universe

• 0:06
  Speaker 1: The best view in the universe is not from the
• 0:08
  Speaker 1: top of the Seer's Tower or the birds Dubai. It's
• 0:12
  Speaker 1: not from some seaside hotel. It's not from the top
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  Speaker 1: of Mount Everest. It's from your backyard. On a dark night.
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  Speaker 1: You can look up at the universe and see across
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  Speaker 1: billions and billions of miles. Every view on Earth pales
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  Speaker 1: in comparison to the vista you see across this ocean
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  Speaker 1: of space. Though they are impossibly distant, you can still
• 0:34
  Speaker 1: see balls of gas furiously fusing, burning brilliantly enough that
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  Speaker 1: they can be seen with your naked eyeball. And if
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  Speaker 1: you look closely, you'll notice something incredible. There's a rainbow
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  Speaker 1: of stars out there. White, blue, yellow, red. It's a
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  Speaker 1: fabulously colorful universe. What does that mean? Why are stars
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  Speaker 1: different colors? We'll be digging into the physics and countering
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  Speaker 1: some usual pop sigh misinformation along the way. Welcome to
• 1:02
  Speaker 1: Daniel and Kelly's extraordinarily fabulous colorful Universe.
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  Speaker 2: Hello, my name is Kelly Windersmith. I study parasites and
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  Speaker 2: space and I love looking at the night sky.
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  Speaker 1: Hi. I'm Daniel. I'm a particle physicist, and I don't
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  Speaker 1: have a favorite color.
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  Speaker 2: I do. Mine's purple. Why don't you have a favorite color?
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  Speaker 1: I don't get the whole principle of choosing a favorite.
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  Speaker 1: Like I like the colors, they're all nice. Why do
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  Speaker 1: I have to pick one and say this one's my
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  Speaker 1: favorite color? Like, I like purple, it's nice. I like orange. Yellow,
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  Speaker 1: it's pretty good too. Blue is so soothing. I like
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  Speaker 1: the colors. Grown do you have a favorite child?
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  Speaker 2: You know? You and Zach. I'll ask Zach what's your favorite?
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  Speaker 2: Blah blah blah, and he's like, I don't see any
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  Speaker 2: reason to pick a favorite. And I'm like, because people
• 1:58
  Speaker 2: use this as a conversation starter, and you're a conversation killer.
• 2:05
  Speaker 1: I was just gonna say, it's the way people start conversations.
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  Speaker 1: But it feels to me like dishonest, it's false. It's
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  Speaker 1: like it's not what you really think or feel. It's
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  Speaker 1: just like, oh, you like red, I like green. You
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  Speaker 1: know it's not sincere, so it doesn't start a good conversation.
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  Speaker 2: I think it's implied that, like, you're not married to
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  Speaker 2: that color for the rest of your life. I was
• 2:24
  Speaker 2: doing a book signing. I was like, oh, so tell
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  Speaker 2: me something about you. And he's like, I hate small talk.
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  Speaker 1: And I was like, oh, okay, and that's the end
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  Speaker 1: of this conversation.
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  Speaker 2: I did stop talking. I was like, okay, all right,
• 2:35
  Speaker 2: I don't know what else to say. Now you've ruined
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  Speaker 2: the question I was planning on asking you today because
• 2:39
  Speaker 2: it involves the word favorite. But I was going to
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  Speaker 2: ask you about your favorite or the best star viewing
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  Speaker 2: experience you've had, Like when was the moment when the
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  Speaker 2: sky was most clear and you could see the farthest.
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  Speaker 1: I think one of my favorite observing moments is not
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  Speaker 1: actually looking at stars, because you know, stars are hard
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  Speaker 1: to make out any features for because they're so far away.
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  Speaker 1: They're sicly just points of light. But stuff in our
• 3:02
  Speaker 1: Solar system that you can actually see. And back in
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  Speaker 1: the mid nineties, I was working on a project over
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  Speaker 1: the summer right when comet shoemaker Levee was about to
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  Speaker 1: slam into Jupiter, and I had access to a super
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  Speaker 1: high speed camera and so we pointed it at Jupiter
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  Speaker 1: hoping to catch really high speed photographs of the impact
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  Speaker 1: to see like, you know, planet sized plumes of fire
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  Speaker 1: emerging from it. It was super cool.
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  Speaker 2: I mean, I do feel like I asked you something
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  Speaker 2: like what's your favorite color? And you answered macaroni and cheese.
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  Speaker 2: But that is a very cool story. Did you see
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  Speaker 2: what you wanted to see?
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  Speaker 1: Yeah, we got to see shoemaker levee impact on Jupiter.
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  Speaker 1: Unfortunately impacted around the back of Jupiter, so we didn't
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  Speaker 1: see the collision itself, but we did see the plume
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  Speaker 1: coming up over the limb of Jupiter. Really pretty amazing.
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  Speaker 1: I sort of remember it in black and white. I
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  Speaker 1: can't really answer your color questions, but Jupiter does have
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  Speaker 1: a lot of beautiful colors. See, it doesn't just pick.
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  Speaker 2: One that's amazing. And you keep sort of wiggling around
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  Speaker 2: my questions. That's fine, that's fine. What you're saying is interesting,
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  Speaker 2: so it's fine for content.
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  Speaker 1: And i'd ask you what your favorite color is, But
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  Speaker 1: you're wearing a color right now. You literally have paint
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  Speaker 1: all over your arms. That's your favorite color.
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  Speaker 2: Well, that's my favorite color for my laundry room renovation
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  Speaker 2: that I'm working on right now. But my favorite star
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  Speaker 2: viewing moment I got really lucky one. So I was
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  Speaker 2: in Costa Rica and I was in a community where
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  Speaker 2: there was a big leather back sea turtle conservation project
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  Speaker 2: going on, and leather back sea turtles can get distracted
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  Speaker 2: by lights and then they move towards those lights and
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  Speaker 2: then they don't go out to the ocean after they
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  Speaker 2: hatch like they're supposed to. So the whole community had
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  Speaker 2: very dim red lights and they turned off all of
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  Speaker 2: their bright lights at night, and so we were sort
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  Speaker 2: of in the middle of nowhere and all the lights
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  Speaker 2: were off. So my job at two am was to
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  Speaker 2: guard the hatchery so that raccoons wouldn't dig up the
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  Speaker 2: leather back sea turtle eggs and eat them.
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  Speaker 1: Wow.
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  Speaker 2: So it was like two am in Costa Rica. It
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  Speaker 2: was the middle of nowhere. All the lights were out,
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  Speaker 2: and it was just the most amazing view of the
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  Speaker 2: Milky Way and you know, shootings stars and at any
• 5:01
  Speaker 2: time there could be baby turtles. Like that's Pete Kelly
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  Speaker 2: life right there. I'd much rather spend time with my kids,
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  Speaker 2: But that was amazing.
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  Speaker 1: That sounds like a magical moment. Did the night sky
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  Speaker 1: look anything like your outfit does right now?
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  Speaker 2: Yeah, except a fewer holes in it. This is also
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  Speaker 2: what I wear. What I'm doing some renovation work. I
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  Speaker 2: don't know, it's comfy.
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  Speaker 1: For the audio only listeners. Kelly's wearing something which looks
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  Speaker 1: like it has star patterns on it.
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  Speaker 2: It does. And my daughter has a matching outfit that
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  Speaker 2: we wear sometimes, and she still wants to wear even
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  Speaker 2: though this dress has holes in it. Whenever she wants
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  Speaker 2: to wear a matching outfit, I am all in because
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  Speaker 2: I imagine it's like weeks or months before she's too
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  Speaker 2: old to want to do that. So every day it's
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  Speaker 2: an automatic.
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  Speaker 1: Yes, You've got to savor those moments when the kids
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  Speaker 1: still want to spend time with you, because pretty soon
• 5:44
  Speaker 1: they're going to grow up and move on.
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  Speaker 2: I know, I know your kid's going to college.
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  Speaker 1: And kids are not the only thing growing up and
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  Speaker 1: changing and moving on. Everything in the universe is going
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  Speaker 1: through its own life cycle, including the stars in the sky,
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  Speaker 1: burning and glowing and changing colors as they do.
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  Speaker 2: Yeah. So when I was listening to your introduction, I
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  Speaker 2: was realizing that I don't appreciate all the colors of
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  Speaker 2: the stars in the sky. I just think of them
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  Speaker 2: as white and sort of look at them as sort
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  Speaker 2: of a blurry something. I don't pay attention to the
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  Speaker 2: individual colors, the palette of the universe. So I'm excited
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  Speaker 2: that next time I look at the night sky, I'll
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  Speaker 2: pay a little bit more attention, and I'm excited to
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  Speaker 2: learn more from you today.
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  Speaker 1: Yeah, the universe is very colorful, but it's not just
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  Speaker 1: to please you or to start conversation among two am
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  Speaker 1: sky watchers who can otherwise talk to each other. It's
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  Speaker 1: for physics reasons, and the colors in the night sky
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  Speaker 1: are going to tell us a lot about what's going
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  Speaker 1: on inside those.
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  Speaker 2: Stars, as long as it's not for chemistry reasons.
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  Speaker 1: So this is actually part one of a two part
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  Speaker 1: series about why stars have colors and what it tells
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  Speaker 1: us about the universe, which ends up with a really
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  Speaker 1: interesting story about yet another overlooked female astronomer.
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  Speaker 2: Oh I love when I'm surprise. While we're recording, I
• 7:01
  Speaker 2: didn't realize this was a two parter.
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  Speaker 1: I just realized as the two parter because I'm preparing
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  Speaker 1: that other episode, and now I'm understanding, Oh my gosh,
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  Speaker 1: this is the perfect setup for that episode. So good
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  Speaker 1: job Daniel realizing that in real time.
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  Speaker 2: Welcome to Star Week.
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  Speaker 1: This is how carefully we plan the episodes on the podcast.
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  Speaker 1: All right, So before we dig deeper, I was curious
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  Speaker 1: if people knew why stars had different colors, and so,
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  Speaker 1: as usual, I went out to our group of wonderful, clever, hilarious,
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  Speaker 1: well informed, good looking volunteers to ask them if you
• 7:35
  Speaker 1: would like to join their ranks for future episodes. Please
• 7:38
  Speaker 1: don't be shy, right to us two questions at Danielankelly
• 7:41
  Speaker 1: dot org. We'll hook you up in the meantime, think
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  Speaker 1: about it for yourself. Do you know why stars are
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  Speaker 1: different colors? Here's what our volunteers had to say. We
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  Speaker 1: know the color here on Earth is based on different
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  Speaker 1: wavelengths of light, so I'm assuming that the same principles
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  Speaker 1: apply to stars.
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  Speaker 3: Red shift the including distance from and speed away from
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  Speaker 3: the observer.
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  Speaker 4: Color of the stars related to its size. So the
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  Speaker 4: older the stars, the more it's been able to fuse,
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  Speaker 4: the heavier elements you get different.
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  Speaker 1: Spectrum their temperature and the element.
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  Speaker 5: I know that big hot stars are described as below
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  Speaker 5: and small coola stars described as red, and middlely ones
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  Speaker 5: like our sun are yellow.
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  Speaker 4: Well, I think the color of stars depends pretty well
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  Speaker 4: solely on their age.
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  Speaker 3: I think stars are different colors based on the levels
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  Speaker 3: of hydrogen and helium in the star.
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  Speaker 4: Red ones are shy, and as they get closer they
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  Speaker 4: turn red.
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  Speaker 1: Blue ones are kind of cool, so they're going away
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  Speaker 1: from you. They don't care.
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  Speaker 2: Different elements of different colors, and stars throughout their life
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  Speaker 2: fuses loads of different elements.
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  Speaker 1: I think stars are different colors because of the gases
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  Speaker 1: that are in them, and also because of the temperature
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  Speaker 1: of the star.
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  Speaker 4: Probably due to their composition, different elements they are made
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  Speaker 4: up of, and perhaps also their size and perhaps just
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  Speaker 4: how they're burning their energy output.
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  Speaker 1: Also, the universe believes in diversity, equity inclusion, and that's
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  Speaker 1: why they're different colors.
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  Speaker 2: The temperatures are different and that causes the black body
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  Speaker 2: radiation peaks to be at different wavelength.
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  Speaker 4: Stars are different colors because they have different elements and
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  Speaker 4: they burn at different temperatures, which changes the color we see.
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  Speaker 4: I'm really not sure where the stars are different colors,
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  Speaker 4: but if I had to guess, I would say it
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  Speaker 4: had to do something with where they were at in
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  Speaker 4: their life cycle and the gases that they are made
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  Speaker 4: up of.
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  Speaker 3: I think stars are different colors because the way they
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  Speaker 3: expand and like the gases inside of them like as
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  Speaker 3: they expand and get hotter, I think they like change
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  Speaker 3: colors and stay those colors their lifetime.
• 9:55
  Speaker 1: I would think that stars are different colors because they
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  Speaker 1: emit different light particles, but I think a nonscience the
• 10:02
  Speaker 1: answer would be that they have a cool aura.
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  Speaker 2: Amazing answers I chuckled, and some really clever insights here.
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  Speaker 2: What did you think, Daniel?
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  Speaker 1: I think there's a lot of interesting stuff going on here.
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  Speaker 1: The picture I'm putting together of what people imagine causes
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  Speaker 1: the different colors of stars is that this different fusion
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  Speaker 1: happening with like different ingredients. Maybe you have more metal
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  Speaker 1: here and more metal there, and that's somehow changing what's
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  Speaker 1: going on, and that's changing the burning of the star
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  Speaker 1: the way you can put copper in a Bunsen burner
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  Speaker 1: and it turns green, for example.
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  Speaker 2: That is my understanding coming into this conversation is that
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  Speaker 2: I do think it depends on what elements are getting
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  Speaker 2: burned and how hot. But often I'm wrong.
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  Speaker 1: So I suspect a lot of you listening out there
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  Speaker 1: probably think the same thing, which is why we do
• 10:47
  Speaker 1: this segment to orient us and understand where we need
• 10:50
  Speaker 1: to take you from your current understanding to a deeper,
• 10:52
  Speaker 1: more physical understanding. So we hope that by the end
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  Speaker 1: of the episode you have a deeper view of why
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  Speaker 1: stars have different colors, because the answer is a little
• 11:00
  Speaker 1: bit more subtle than anything we heard from our volunteers.
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  Speaker 2: All Right, I love it. Let's dig in and let's
• 11:05
  Speaker 2: start with the basics. Tell me about light and color.
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  Speaker 1: Right, So some of the listeners commented that different colors
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  Speaker 1: mean different wavelengths, and that's true. Of course we're interested
• 11:13
  Speaker 1: in like why is flight emitted at different wavelengths? But
• 11:16
  Speaker 1: fundamentally it's important to understand the physical mechanism here, like
• 11:19
  Speaker 1: why are we seeing different colors? And they're right, because
• 11:22
  Speaker 1: light is electromagnetic radiation. The universe is filled with electromagnetic field,
• 11:27
  Speaker 1: and that field can ripple, and when electrons in alpha
• 11:30
  Speaker 1: centauri wiggle, they cause ripples in that field because electrons
• 11:34
  Speaker 1: are connected to that field. Right, When electron moves, it
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  Speaker 1: wiggles that field, and that wiggle is what we see
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  Speaker 1: as photons, for example. And those wiggles have frequencies, and
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  Speaker 1: the frequencies correspond to different wavelengths, and those wavelengths correspond
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  Speaker 1: to colors.
• 11:50
  Speaker 2: I feel like a bunch of pieces actually just click
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  Speaker 2: together in my head that should have clicked together much earlier,
• 11:55
  Speaker 2: but there they are, okay.
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  Speaker 1: Click And the same mechanism is like how radio works
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  Speaker 1: wizer an antenna because electrons are going up and down
• 12:03
  Speaker 1: in the antenna, and as they do so, they make
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  Speaker 1: the photon field wiggle just the same way, like if
• 12:07
  Speaker 1: you're holding the end of a jump rope and you
• 12:09
  Speaker 1: go up and down, you make wiggles down the jump rope.
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  Speaker 1: It's exactly the same mechanism.
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  Speaker 2: I think the piece is just unclicked. Oh no, I
• 12:17
  Speaker 2: think I don't understand the electrons going up and down
• 12:20
  Speaker 2: the antenna. Thing is it just radio waves are traveling
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  Speaker 2: through the antenna and that's radio frequencies.
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  Speaker 1: Well, an electron has an electric field around it, right,
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  Speaker 1: If the electron just sits there, the electric field doesn't change.
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  Speaker 1: What happens if the electron moves up, well, the electric
• 12:34
  Speaker 1: field also has to move up. Or if the electron
• 12:36
  Speaker 1: field moves up and then down, the electric field moves
• 12:39
  Speaker 1: up and then down. But it doesn't do so instantly,
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  Speaker 1: Like if you wiggle an electron in an antenna that's
• 12:44
  Speaker 1: a mile away from me, I don't instantly see it
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  Speaker 1: change in the electric field. It has to propagate and
• 12:50
  Speaker 1: So if the electron is going constantly up and down
• 12:52
  Speaker 1: and up and down, then it's making waves up and
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  Speaker 1: down in the electric field that propagate out away from it.
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  Speaker 1: And if I'm a mile away and i have electrons
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  Speaker 1: in my antenna, those wiggles in the electric field are
• 13:02
  Speaker 1: going to push on my antenna's electrons, which are going
• 13:05
  Speaker 1: to go up and down, and then I'm going to
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  Speaker 1: read that out as current. So yeah, the electrons in
• 13:10
  Speaker 1: descending antenna wiggle the electric field, which wiggles. Electrons in
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  Speaker 1: the receiving antenna, which move and can be picked up
• 13:16
  Speaker 1: by my electronics can be reclick yep, yah yah. And
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  Speaker 1: so the different colors are different wavelengths of those wiggles.
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  Speaker 1: Photons are wiggles in the electromagnetic field, but they can
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  Speaker 1: have different wavelengths. Right. They can be really really narrow,
• 13:32
  Speaker 1: so they're like very high frequency, like ultraviolet or purple.
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  Speaker 1: They can be really really long, so they're like radio
• 13:38
  Speaker 1: waves or red light or infrared light. And there's a
• 13:41
  Speaker 1: potential source of confusion here. Remember these things are quantum mechanicals,
• 13:45
  Speaker 1: So photons are discrete units. Like you can have one
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  Speaker 1: photon or two photons, but you can't have two point
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  Speaker 1: seven eighty one photons, but you can have photons of
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  Speaker 1: any energy. That's a continuous spectrum, So there's an infinite
• 13:58
  Speaker 1: number of frequencies on the spectrum.
• 14:01
  Speaker 2: So does that mean there's an infinite number of colors?
• 14:04
  Speaker 1: Mmmm, yes, great question. Right, So there are an infinite
• 14:08
  Speaker 1: number of frequency choices for a photon. But colors are
• 14:11
  Speaker 1: things that we experience in our mind. Right. There are
• 14:15
  Speaker 1: responds to signals on the optic nerve. So let's talk
• 14:18
  Speaker 1: momentarily about the physics of the biology of what's going
• 14:21
  Speaker 1: on there. You have photons that enter your eyeball and
• 14:23
  Speaker 1: they hit the back of the eyeball and the back
• 14:25
  Speaker 1: of the eyeball, there are three different kinds of cells
• 14:27
  Speaker 1: that respond to different colors. They have proteins on them
• 14:31
  Speaker 1: that operate like little switches, and when they absorb a
• 14:33
  Speaker 1: photon of the right color, they flip that switch and
• 14:36
  Speaker 1: they send a signal up the optic nerve. This whole
• 14:38
  Speaker 1: continuous spectrum of photons gets converted into three numbers, how
• 14:43
  Speaker 1: much did you turn on cone one, Cone two, and
• 14:45
  Speaker 1: cone three? And then your brain interprets those and generates
• 14:49
  Speaker 1: the experience of the color. So the color is actually
• 14:52
  Speaker 1: in your mind. It's not on the photon, right, we
• 14:55
  Speaker 1: say red photon or green photon when we're being sloppy,
• 14:59
  Speaker 1: but really the boon has an energy and the experience
• 15:01
  Speaker 1: of color is only in your brain.
• 15:03
  Speaker 2: And we got a great question on our discord channel,
• 15:06
  Speaker 2: which you can join by going over to Danielankelly dot
• 15:09
  Speaker 2: org and clicking the invite and Quicksilver the DIRG Sorr
• 15:14
  Speaker 2: who was the discord quicksilver the DIRG anyway, this individual
• 15:20
  Speaker 2: going by the moniker Quicksilver, the DIRG wanted to know
• 15:23
  Speaker 2: something about why we see the colors that we do see.
• 15:26
  Speaker 2: And actually, our distant ancestors had two kinds of light
• 15:30
  Speaker 2: cones and we have three, and so why do we
• 15:33
  Speaker 2: see the colors that we see. The answer, really, at
• 15:36
  Speaker 2: the end of the day is we're not one hundred
• 15:37
  Speaker 2: percent sure, but we think what happens is that there
• 15:40
  Speaker 2: was a gene duplication event, and these happens every once
• 15:42
  Speaker 2: in a while in our genome. And so now instead
• 15:44
  Speaker 2: of having two different kinds of cones, you had two
• 15:48
  Speaker 2: different kinds of cones, but three different genes for those cones,
• 15:51
  Speaker 2: and over time selection tinkered with that extra new gene
• 15:55
  Speaker 2: and we ended up with the ability to see the
• 15:58
  Speaker 2: color red. Already see things like green, and the thought
• 16:01
  Speaker 2: was that seeing colors like red allowed our primate ancestors
• 16:05
  Speaker 2: to differentiate between different kinds of fruits and in particular
• 16:09
  Speaker 2: whether or not the fruits were ripe. And there are
• 16:11
  Speaker 2: some macaques that only have two types of cones and
• 16:14
  Speaker 2: some macaques that have three types of cones in the
• 16:16
  Speaker 2: same species, there's this variability. Some studies have found that
• 16:20
  Speaker 2: if you have three types of cones, you get ripe
• 16:22
  Speaker 2: fruits quicker and eat them quicker, which shows a benefit.
• 16:25
  Speaker 2: But other studies and other kinds of macaques haven't found
• 16:28
  Speaker 2: that because it's biology, so it depends depends there you go.
• 16:32
  Speaker 1: And I think you put your finger on it, because
• 16:34
  Speaker 1: the important thing here is the ability to distinguish different colors, right,
• 16:37
  Speaker 1: But I think that depends not just on like the
• 16:39
  Speaker 1: number of different kinds of cones you have, but also
• 16:42
  Speaker 1: the processing power behind it. I know that like mantis,
• 16:45
  Speaker 1: shrimp are famous for having like more than ten different
• 16:48
  Speaker 1: kinds of cones, but they actually apparently are terrible at
• 16:51
  Speaker 1: distinguishing different colors because they have almost no neural processing
• 16:55
  Speaker 1: behind it. I think they might just like experience ten
• 16:58
  Speaker 1: different literal colors. We have a huge number of different
• 17:02
  Speaker 1: colors that we can distinguish because we can do this interpolation, right,
• 17:06
  Speaker 1: That's what your brain is doing is it's getting like, oh,
• 17:08
  Speaker 1: a little bit from the bluish cone, a little bit
• 17:10
  Speaker 1: from the reddish cone, a little bit from the greenish cone,
• 17:12
  Speaker 1: and it's saying, okay, what color would give me this
• 17:15
  Speaker 1: pattern and then sort of inferring what color might be there.
• 17:18
  Speaker 1: But again, the experience of color, the reason like red
• 17:21
  Speaker 1: is reddish and blue is bluish has nothing to do
• 17:23
  Speaker 1: with the photon. That's something your brain has assigned to
• 17:26
  Speaker 1: it has invented, has fabricated. Right in principle, it could
• 17:30
  Speaker 1: make up a new color. If you've got a new
• 17:32
  Speaker 1: cone and planted that was sensitive to the ultraviolet, that
• 17:34
  Speaker 1: your brain could invent a new experience, not one that's
• 17:38
  Speaker 1: a combination of the other ones, but like a real
• 17:40
  Speaker 1: novel experience to represent the signal from the UV cone.
• 17:44
  Speaker 2: And there are insects that can see in the UV.
• 17:46
  Speaker 2: And it makes me so sad when I look at
• 17:48
  Speaker 2: a beautiful flower and think there's layers that I'm missing.
• 17:51
  Speaker 2: But anyway, I'm guessing based on our examples that you
• 17:54
  Speaker 2: and I both read An Immense World by Ed Young,
• 17:56
  Speaker 2: because we both seem to have cherry picked examples from
• 17:58
  Speaker 2: that fantastic book.
• 18:01
  Speaker 1: It is definitely a great book, a lot of fun,
• 18:02
  Speaker 1: and recommend everybody read that, especially if you're interested in
• 18:05
  Speaker 1: physics and biology, because it covers both of those topics
• 18:08
  Speaker 1: about our experience.
• 18:09
  Speaker 2: Okay, so the three kind of cones that we have
• 18:12
  Speaker 2: determine what colors we can see in the night sky.
• 18:15
  Speaker 2: Are we missing a lot or are there ultraviolet stars
• 18:18
  Speaker 2: out there that we're missing.
• 18:20
  Speaker 1: We're definitely missing a lot because we can only see
• 18:21
  Speaker 1: a certain range of photons ultraviolet and infrared. Everything below
• 18:25
  Speaker 1: that and everything above that we can't see, and the
• 18:27
  Speaker 1: sky definitely is bright in those colors. That's why, for example,
• 18:31
  Speaker 1: we have radio telescopes and infrared telescopes and ultraviolet telescopes
• 18:35
  Speaker 1: because stars and other different phenomena emit differently in those
• 18:39
  Speaker 1: spectrum and if you can see those, you can see
• 18:41
  Speaker 1: different kinds of things. Also, the universe is transparent differently
• 18:46
  Speaker 1: in different frequencies. Some frequencies of life can go through
• 18:49
  Speaker 1: dust clouds and others can't, and so if you want
• 18:52
  Speaker 1: to see through dust clouds, you've got to change your frequency.
• 18:55
  Speaker 1: So absolutely the night sky looks very different outside the
• 18:58
  Speaker 1: visible range our star, and of course peaks right in
• 19:01
  Speaker 1: the center of the visible range, which again is no coincidence. Right.
• 19:05
  Speaker 1: If you're going to evolve vision, you might as well
• 19:07
  Speaker 1: evolve it to be able to see the most common
• 19:09
  Speaker 1: photons that are around you. So if we had evolved
• 19:12
  Speaker 1: around a redder star, for example, probably our visible range
• 19:15
  Speaker 1: would be lower. The Sun is an unusual star. Most
• 19:18
  Speaker 1: of the stars out there are redder than our star.
• 19:21
  Speaker 1: Our star is yellower than most stars out there, so
• 19:24
  Speaker 1: we may have a different visual range than most of
• 19:26
  Speaker 1: the aliens.
• 19:27
  Speaker 2: So are you postulating that the color of the star
• 19:30
  Speaker 2: determines the colors that we see, because I feel like
• 19:33
  Speaker 2: that's not an evolutionary argument that I understand. Does the
• 19:36
  Speaker 2: color of our star impact the color of things on
• 19:39
  Speaker 2: Earth that are important for food, mating or running away
• 19:42
  Speaker 2: from a predator?
• 19:43
  Speaker 1: I think it makes sense for us to be most
• 19:45
  Speaker 1: sensitive to the photons that are most present here on
• 19:48
  Speaker 1: Earth for that range. Whether we can experience two or
• 19:51
  Speaker 1: seven or three or whatever, I think is a different question.
• 19:54
  Speaker 1: But for us to be sensitive to the most common
• 19:57
  Speaker 1: kind of photons makes sense to me. I'll give you
• 20:00
  Speaker 1: that you're skeptical. Why A you're skeptical?
• 20:02
  Speaker 2: So I totally follow the argument that the most common
• 20:04
  Speaker 2: kinds of photons in the environment would be the ones
• 20:06
  Speaker 2: that were good to sense. But if for some reason
• 20:10
  Speaker 2: those didn't translate into an increased ability to find your
• 20:15
  Speaker 2: food or an increased ability to recognize a mate, then
• 20:19
  Speaker 2: I don't necessarily think that selection would hone in on those.
• 20:22
  Speaker 2: And there's so much variability and what animals can see.
• 20:24
  Speaker 2: You know, there's plenty of dichromates, so they don't have
• 20:27
  Speaker 2: three kinds of cones and they get along just fine.
• 20:30
  Speaker 2: So yeah, how do you explain the variability?
• 20:32
  Speaker 1: Then that's a great point. And I can give you
• 20:34
  Speaker 1: an example to support your point, which is neutrinos. Neutrinos
• 20:37
  Speaker 1: are everywhere in our environment, but pretty much useless because
• 20:41
  Speaker 1: everything is transparent to them, and so it wouldn't be
• 20:44
  Speaker 1: great to develop a neutrino eyeball even though they're everywhere.
• 20:48
  Speaker 1: So you're right, just being ubiquitous isn't enough to have
• 20:50
  Speaker 1: to be useful. And so I think the combination of
• 20:53
  Speaker 1: the fact that they are everywhere, and stuff on Earth
• 20:56
  Speaker 1: tends to not be transparent to them, makes them useful
• 20:59
  Speaker 1: for us to see things. So I think you're right.
• 21:01
  Speaker 1: It's more complicated than just the physics of this region
• 21:04
  Speaker 1: has to also be like useful in your environment. For sure.
• 21:07
  Speaker 1: I have no idea why you would have two or
• 21:09
  Speaker 1: seven cones.
• 21:11
  Speaker 2: I guess both of our fields are useful. You ponder
• 21:14
  Speaker 2: the question Daniel and I were just debating during the break,
• 21:17
  Speaker 2: And when we get back, we'll talk about why stars
• 21:19
  Speaker 2: have different colors? All right, and we're back. You look
• 21:39
  Speaker 2: up at the night sky and there are lots of
• 21:41
  Speaker 2: different colors of stars. Though I'll be honest, I missed
• 21:43
  Speaker 2: that in the past. I'm gonna be paying much more
• 21:45
  Speaker 2: attention now. So Daniel, why do those stars have different colors?
• 21:50
  Speaker 1: So there's sort of three big factors that control what
• 21:53
  Speaker 1: color a star is in our sky. One is what
• 21:56
  Speaker 1: it's made out of, another one is its temperature, and
• 22:00
  Speaker 1: the last one is its velocity. So let's do those
• 22:02
  Speaker 1: in order. What it's made out of. This is the
• 22:05
  Speaker 1: one that's connected to your experience of like putting copper
• 22:07
  Speaker 1: in a Bunsen burner and seeing it glow green. That's
• 22:10
  Speaker 1: because atoms are quantum mechanical little objects and they have
• 22:14
  Speaker 1: energy levels. You know, electrons around an atom can't just
• 22:17
  Speaker 1: be at any energy willy nilly. There's a ladder of
• 22:19
  Speaker 1: energies there, and because there's a ladder of energies there,
• 22:22
  Speaker 1: they can only eat and emit photons of certain energies,
• 22:26
  Speaker 1: the ones that let them go up or down the ladder.
• 22:28
  Speaker 1: So when an electron is around an atom and a
• 22:30
  Speaker 1: photon comes by, if that photon has just the right
• 22:34
  Speaker 1: energy to take it up one or two or seven
• 22:36
  Speaker 1: rungs on that ladder, it can eat that photon. You
• 22:39
  Speaker 1: might think I don't care about what photons the electron eats,
• 22:42
  Speaker 1: but actually does matter what it absorbs and what it reflects,
• 22:45
  Speaker 1: because what it reflects is what you see. Right, If
• 22:48
  Speaker 1: you're looking at something that's blue, it's not blue because
• 22:50
  Speaker 1: it's eating blue photons. It's blue because it's eating everything
• 22:54
  Speaker 1: but the blue photons. It's reflecting blue photons back at you.
• 22:58
  Speaker 1: Remember you see something blue because some light in the
• 23:01
  Speaker 1: blue range has hit your eyeball and you responded to that.
• 23:05
  Speaker 1: So it's important what energy levels an atom can absorb.
• 23:09
  Speaker 1: And the same is true also in the reverse, Adam's
• 23:11
  Speaker 1: in midlight. That's what's happening to the copper in your
• 23:13
  Speaker 1: Bunsen burner. It's getting hot, and the inverse process is happening.
• 23:17
  Speaker 1: An electron jumps down energy levels and gives off a photon,
• 23:20
  Speaker 1: a green photon in the case of copper.
• 23:22
  Speaker 2: That always felt very counterintuitive to me, that the color
• 23:26
  Speaker 2: that I'm seeing is the color that's being given off
• 23:28
  Speaker 2: by something. It almost feels like everything is disguising itself
• 23:32
  Speaker 2: in some way. I don't I don't know why my
• 23:34
  Speaker 2: brain ahead trouble wrapping itself around that.
• 23:36
  Speaker 1: I totally remember the first time I understood that. I
• 23:38
  Speaker 1: was like nine, and I was like, oh my gosh,
• 23:41
  Speaker 1: things that are blue are not actually blue, they just
• 23:43
  Speaker 1: look blue. And then I realized, well, maybe that's what
• 23:46
  Speaker 1: it means to be blue, to look blue. But yeah,
• 23:48
  Speaker 1: I had the sense that like, if I could see
• 23:50
  Speaker 1: through these photons to what things actually looked like, I
• 23:54
  Speaker 1: could perceive a deeper truth to the universe. But the
• 23:56
  Speaker 1: universe is kind of a construct we've assembled in our
• 23:58
  Speaker 1: head from our experience of it, and there's a lot
• 24:01
  Speaker 1: of that that's imagined, that's put together from our experience
• 24:04
  Speaker 1: and the way we paint these colors on things is
• 24:07
  Speaker 1: just one layer of that.
• 24:08
  Speaker 2: Yeah, man, Yeah, I totally agree though.
• 24:15
  Speaker 1: Yeah, but that's the joy physics. It helps you separate
• 24:17
  Speaker 1: what's really out there and what you know about it,
• 24:19
  Speaker 1: which you don't know about it, which parts you're building
• 24:22
  Speaker 1: in your mind. Super fascinating, even if it is philosophical
• 24:25
  Speaker 1: and could never be understood. So the next piece to
• 24:27
  Speaker 1: understand is why things have different colors? Right, We said
• 24:30
  Speaker 1: that atoms have energy levels, and electrons can jump up
• 24:34
  Speaker 1: energy levels eating photons or down energy levels emitting photons,
• 24:38
  Speaker 1: and those photons have specific energies corresponding to those gaps. Well,
• 24:42
  Speaker 1: different atoms have different energy levels. Copper and mercury and
• 24:46
  Speaker 1: helium and hydrogen all have different energy levels. Because the
• 24:50
  Speaker 1: solutions to the Shorteninger equation are different, you got different
• 24:52
  Speaker 1: numbers of protons, and the whole configuration of the atom
• 24:55
  Speaker 1: is different. Every atom has its own unique ladder, which
• 24:58
  Speaker 1: means that they have like a fingerp If you take
• 25:01
  Speaker 1: an element and you take a gas of it and
• 25:02
  Speaker 1: heat it up, and then you take the light from
• 25:04
  Speaker 1: that pass it through a prism to spread it out,
• 25:07
  Speaker 1: you'll see that Each element has its own unique fingerprint,
• 25:11
  Speaker 1: its own spectrum. They'll have these little bands like a
• 25:14
  Speaker 1: blue one and a red one, or a different element
• 25:16
  Speaker 1: will have like a green band and the blue band
• 25:18
  Speaker 1: will be shifted over. So you can tell what something
• 25:21
  Speaker 1: is made out of just by looking at a spectrum
• 25:23
  Speaker 1: of a hot gas. So there's two things that are
• 25:25
  Speaker 1: happening here. You have hot gas, it glows in certain colors, right,
• 25:29
  Speaker 1: And if you have more oxygen, you glow in these colors.
• 25:31
  Speaker 1: You have more neon, you glow in those colors. And
• 25:33
  Speaker 1: our whole next episode is going to be about using
• 25:35
  Speaker 1: spectroscopy to understand what stars are made out of. But
• 25:39
  Speaker 1: this also absorption, Right, if a star has an atmosphere
• 25:42
  Speaker 1: and that atmosphere is mostly neon, for example, then it's
• 25:45
  Speaker 1: going to absorb that light. So if you have a
• 25:48
  Speaker 1: hot blob of gas, it emits light to those frequencies.
• 25:51
  Speaker 1: If you have light that passes through an atmosphere, then
• 25:54
  Speaker 1: it absorbs those frequencies.
• 25:57
  Speaker 2: So it feels to me now like we have an
• 26:00
  Speaker 2: infinite number of combinations of elements that could be emitting
• 26:03
  Speaker 2: and like gases that could be absorbing. How do we
• 26:06
  Speaker 2: make sense of the output given that there's now so
• 26:09
  Speaker 2: many different options, and it's probably not just one element
• 26:11
  Speaker 2: that's emitting at a time. There's probably a couple different
• 26:13
  Speaker 2: things that are emitting. And I'm overwhelmed.
• 26:16
  Speaker 1: Yes, it is overwhelming. It's a hard problem, and it
• 26:18
  Speaker 1: was solved by a very clever young lady around the
• 26:20
  Speaker 1: turn of the century. And we're going to talk about
• 26:22
  Speaker 1: that in the next episode. Okay, but even if you
• 26:24
  Speaker 1: mix all these elements together, what you get are a
• 26:27
  Speaker 1: bunch of different spikes Like these are narrow emission lines.
• 26:30
  Speaker 1: You can't put them together to get a broad spectrum.
• 26:32
  Speaker 1: And that's not what most of the light from the
• 26:34
  Speaker 1: stars is. This is like people's conception, but most of
• 26:37
  Speaker 1: the light from the star comes from a completely different process.
• 26:40
  Speaker 1: It's not from atomic emission and absorption. It comes from
• 26:44
  Speaker 1: the plasma inside the star just glowing at a certain temperature.
• 26:48
  Speaker 2: What all right, we were all wrong, audience and friends
• 26:51
  Speaker 2: of mine. Okay, so Daniel, let's move on to the
• 26:54
  Speaker 2: next thing. Then tell us more about this thing that
• 26:55
  Speaker 2: actually contributes most of the color.
• 26:57
  Speaker 1: Yeah, so we said that the color of stars comes
• 26:59
  Speaker 1: from what they're made out of, and that has to
• 27:01
  Speaker 1: do with atomic absorption, and emission mostly in the atmosphere
• 27:04
  Speaker 1: of stars, but also from its temperature. And so that's
• 27:07
  Speaker 1: what we're going to dig into next. And there's a
• 27:09
  Speaker 1: process here that has a terrible, absolutely, terrible, very misleading name.
• 27:13
  Speaker 1: It's called black body radiation that describes why stars glow
• 27:17
  Speaker 1: at certain temperatures. And it's terribly the name because a
• 27:19
  Speaker 1: star doesn't seem like a black body. Right.
• 27:22
  Speaker 2: Nope, you guys did it again.
• 27:23
  Speaker 1: But in physics, we have a model of some hypothetical
• 27:26
  Speaker 1: object with no reflection, Like any photon you shoot at
• 27:29
  Speaker 1: it, it will absorb it and just like heat up. And
• 27:32
  Speaker 1: even in the hypothetical version, it's not black. It just
• 27:34
  Speaker 1: means that it doesn't reflect. It glows because of its temperature.
• 27:38
  Speaker 1: Everything in the universe that has a temperature and is
• 27:41
  Speaker 1: made of charged particles will glow. Like if you have
• 27:43
  Speaker 1: fluorescent lights in your ceiling, you look up that has
• 27:46
  Speaker 1: a hot gas in it that's glowing because of its temperature.
• 27:49
  Speaker 1: Or you're glowing right now, Kelly, because of your temperature.
• 27:53
  Speaker 1: Not in the visible light, but if I put on
• 27:55
  Speaker 1: night vision goggles or infrared goggles, I would be able
• 27:58
  Speaker 1: to see you emitting light.
• 28:00
  Speaker 2: What is the physics definition of glow is it just
• 28:02
  Speaker 2: releasing photons or something.
• 28:04
  Speaker 1: It's just releasing photons because you have charge particles in you,
• 28:08
  Speaker 1: and charge particles are always interacting and moving around and whizzing,
• 28:11
  Speaker 1: and when they do so, they emit photons. Like an
• 28:14
  Speaker 1: electron can't change directions without emitting a photon. That's how
• 28:18
  Speaker 1: it does it. And an electron is flying to the
• 28:20
  Speaker 1: universe and it wants to curve along a magnetic fields
• 28:22
  Speaker 1: or something, it's got to push out a photon in
• 28:24
  Speaker 1: the other direction to conserve momentum. Now you have a
• 28:27
  Speaker 1: big blob of gas with all sorts of charge particles
• 28:30
  Speaker 1: whizzing around, they're going to be constantly emitting photons, and
• 28:33
  Speaker 1: they emit a very broad spectrum. Not like the atoms
• 28:36
  Speaker 1: we talked about, we have very specific energy levels. This
• 28:39
  Speaker 1: black body radiation is a very broad spectrum, but it
• 28:42
  Speaker 1: has a peak that depends on the temperature. So really
• 28:44
  Speaker 1: cold things tend to emit in the infrared. Warmer things
• 28:47
  Speaker 1: emit invisible. So for example, you take a piece of metal,
• 28:51
  Speaker 1: it's glowing right now, even if it's cold, just in
• 28:54
  Speaker 1: the infrared. You can't see it. Put in the oven,
• 28:56
  Speaker 1: heated up, put it in the forge. It starts to
• 28:58
  Speaker 1: glow red, and then it glows white. Right. White? Hot
• 29:01
  Speaker 1: is very hot? Why because now it's hot enough to
• 29:04
  Speaker 1: be glowing in the visible Keep heating it up. It'll
• 29:07
  Speaker 1: start to glow in the ultra violet. You won't see
• 29:09
  Speaker 1: it anymore, but it be super duper hot. The temperature
• 29:12
  Speaker 1: of something determines the peak of its emission, right, So
• 29:15
  Speaker 1: everything in the universe that's made of charge particles glows
• 29:18
  Speaker 1: at a certain temperature, and that temperature controls the frequency
• 29:21
  Speaker 1: of the emission.
• 29:23
  Speaker 2: Okay, all right, a few questions. So when an electron
• 29:25
  Speaker 2: kicks out a photon, is it still an electron?
• 29:28
  Speaker 1: It's still an electron because a photon is neutral. Yeah.
• 29:30
  Speaker 2: How many photons can an electron kick out? Can I
• 29:33
  Speaker 2: just do that all the time?
• 29:36
  Speaker 1: Oh my gosh, what an amazing question. It makes me
• 29:39
  Speaker 1: think of an electron as like having a bag of
• 29:41
  Speaker 1: photons that they could run out of, right, like fuel
• 29:44
  Speaker 1: You think of like rockets, right, and they need some source. No,
• 29:47
  Speaker 1: an electron has an infinite number of photons. Remember, these
• 29:50
  Speaker 1: are just wiggles in the electromagnetic field, right, And so
• 29:53
  Speaker 1: it's not like it's kicking off some substance. But in
• 29:57
  Speaker 1: order to conserve momentum, you have to have some momentum
• 29:59
  Speaker 1: move to the ectromagnetic field and some momentum moves through
• 30:02
  Speaker 1: the electron field.
• 30:03
  Speaker 2: Wow, okay, all right. So say you've got some iron,
• 30:07
  Speaker 2: and we talked about iron having emission line spectrums where
• 30:12
  Speaker 2: the electrons get excited and they jump to different levels
• 30:15
  Speaker 2: and they emit light and then you hate that iron
• 30:19
  Speaker 2: up and now it's glowing. Are you saying that the
• 30:22
  Speaker 2: glow is more important than the jumping of the levels.
• 30:28
  Speaker 1: The most general answer is that it depends on what
• 30:31
  Speaker 1: it's made out of and its temperature, and in the
• 30:33
  Speaker 1: case of stars, it's mostly black body radiation. Like when
• 30:36
  Speaker 1: we look at the spectrum from the Sun, it's almost
• 30:39
  Speaker 1: all black body radiation. So that's definitely the most important effect.
• 30:43
  Speaker 1: And there's a combination of the two things. So you
• 30:45
  Speaker 1: have the star which is glowing very broad spectrum which
• 30:48
  Speaker 1: peaks right in the middle of our visual spectrum for
• 30:50
  Speaker 1: our star. But then the sun has an atmosphere, and
• 30:53
  Speaker 1: this atmosphere is gas and it's made out of various stuff,
• 30:56
  Speaker 1: and that atmosphere will eat that spectrum. So the light
• 31:00
  Speaker 1: we get from the Sun is a huge black body
• 31:02
  Speaker 1: peak with a few lines removed. That's absorption spectrum. So
• 31:07
  Speaker 1: if you look at the spectrum from the sun, you
• 31:09
  Speaker 1: see reds and yellows and greens and blues, but then
• 31:12
  Speaker 1: you see these black spots, these things that have been removed.
• 31:15
  Speaker 1: That tells you what's in the atmosphere of the Sun.
• 31:17
  Speaker 1: You can see the hydrogen lines have been removed, the
• 31:19
  Speaker 1: sodium lines, the helium lines, the magnesium lines, and so
• 31:22
  Speaker 1: that helps you figure out what's in the atmosphere of
• 31:24
  Speaker 1: the Sun. So the two things happening there is the
• 31:26
  Speaker 1: broad glow inside the sun, which we're not fully seeing
• 31:29
  Speaker 1: because parts of it have been removed as the Sun's
• 31:32
  Speaker 1: atmosphere eats some of those frequencies.
• 31:35
  Speaker 2: That's amazing.
• 31:36
  Speaker 1: Yeah, and so the last piece we talked about for
• 31:38
  Speaker 1: what determines the light that comes from a star is
• 31:41
  Speaker 1: the velocity. And a bunch of listeners pointed this out
• 31:43
  Speaker 1: that things that are moving away from you will be
• 31:45
  Speaker 1: red shifted, just like a police siren moving away from
• 31:48
  Speaker 1: you will have a lower sound than a police siren
• 31:50
  Speaker 1: moving towards you. It's just a Doppler effect. And so
• 31:53
  Speaker 1: as star emitting light as it moves away from you
• 31:55
  Speaker 1: is going to get red shifted, and we use this
• 31:57
  Speaker 1: red shift to measure that velocity. It's like a huge
• 32:00
  Speaker 1: the important thing in astronomy. A star moving towards you
• 32:03
  Speaker 1: would be blue shifted, and we can tell the red
• 32:05
  Speaker 1: shift in the blue shift because we know the typical fingerprints.
• 32:09
  Speaker 1: Like you get a star you've never seen before and
• 32:11
  Speaker 1: you want to measure its red shift. Well, you might think, well,
• 32:13
  Speaker 1: how it I know it's impossible. If the star has
• 32:15
  Speaker 1: hydrogen lines but they're shifted by a few nanometers, and
• 32:19
  Speaker 1: it has magnesium lines and those are shifted by the
• 32:21
  Speaker 1: same number of nanometers, then the most likely scenario is, oh,
• 32:25
  Speaker 1: this isn't made of some new super weird metal that
• 32:28
  Speaker 1: looks like magnesium and hydrogen but shifted. It's just magnesium
• 32:31
  Speaker 1: and hydrogen and it's been shifted due to the red shift.
• 32:34
  Speaker 1: So you can fit these lines, these specter, these absorption
• 32:37
  Speaker 1: and emission lines, to tell you the frequency shift of
• 32:40
  Speaker 1: an individual star. And so that definitely affects the color
• 32:44
  Speaker 1: of the star in the sky. And almost everything in
• 32:46
  Speaker 1: the sky is moving away from us, so they're all
• 32:49
  Speaker 1: red shifted.
• 32:50
  Speaker 2: I'm having one of those moments where I'm just so
• 32:52
  Speaker 2: proud of our species for figuring all of this out,
• 32:55
  Speaker 2: Like that's so many different things to keep track of.
• 32:57
  Speaker 2: It's so incredible that we got there and that we
• 33:00
  Speaker 2: understand all of this stuff and anyway way to go humans.
• 33:03
  Speaker 1: This is the amazing thing about astronomy is that you
• 33:05
  Speaker 1: cannot leave the Earth. Mostly you've got to figure out
• 33:08
  Speaker 1: the puzzle of the universe from these clues. And we
• 33:11
  Speaker 1: didn't assemble this experiment in this way. We stumbled over
• 33:14
  Speaker 1: these things. People had moments of insight where they realized,
• 33:17
  Speaker 1: hold on a second, this pattern actually reveals this thing
• 33:20
  Speaker 1: about the universe. Those are incredible realizations, so powerful. And
• 33:25
  Speaker 1: let me just qualify what I said a moment ago
• 33:26
  Speaker 1: about everything moving away from us. Galaxies are moving away
• 33:30
  Speaker 1: from us, and those are all red shifted. Most of
• 33:32
  Speaker 1: the stars in the Milky Way are held together by
• 33:34
  Speaker 1: the gravity of the Milky Way, and so those aren't
• 33:37
  Speaker 1: red shifted and moving away from us. The stars in
• 33:40
  Speaker 1: the night sky are the ones from the Milky Way.
• 33:42
  Speaker 1: Those are the ones we can see. They're not red shifted.
• 33:44
  Speaker 1: But other galaxies are red shifted.
• 33:46
  Speaker 2: All right, Well, that is amazing. Let's take a break,
• 33:49
  Speaker 2: and when we get back, we're going to talk about
• 33:51
  Speaker 2: the color of our very own sun. All Right, we're back,
• 34:10
  Speaker 2: and Daniel wants to tell us about why Niel de
• 34:12
  Speaker 2: grass Tyson is wrong.
• 34:14
  Speaker 1: I don't want to say that. I do want to
• 34:17
  Speaker 1: dismantle a lot of pop sign myths that you.
• 34:19
  Speaker 2: Hear from Neil de grass Tyson.
• 34:22
  Speaker 1: I didn't say that. I didn't say that. I just
• 34:24
  Speaker 1: want to say that, you know, on this podcast, we'd
• 34:26
  Speaker 1: like to dig deep, well past the usual pop side
• 34:29
  Speaker 1: explanations and tell you what's really going on. So you know,
• 34:32
  Speaker 1: we're interested in the colors of the stars in general.
• 34:34
  Speaker 1: But of course our sun is near and dear to
• 34:36
  Speaker 1: our hearts. Why does the sun have its particular color?
• 34:40
  Speaker 1: And the Sun's color is actually fascinating because if you
• 34:42
  Speaker 1: were out in space and you were looking at the sun,
• 34:45
  Speaker 1: it's white, right, And what does it mean for the
• 34:47
  Speaker 1: sun to be white? White isn't like a color. It's
• 34:49
  Speaker 1: a mixture of the colors, and it's sort of the
• 34:51
  Speaker 1: way your brain responds when you see a very broad
• 34:55
  Speaker 1: spectrum of light across the visible range. So out of space,
• 34:58
  Speaker 1: the sun is white. Here on Earth because of the
• 35:01
  Speaker 1: effects of the atmosphere. The sun looks a little yellower, right,
• 35:05
  Speaker 1: because the atmosphere tends to scatter blue light, which is
• 35:07
  Speaker 1: why the sky, which doesn't have its color of its own,
• 35:10
  Speaker 1: looks blue, right, because it's reflecting blue light. Air itself
• 35:14
  Speaker 1: is not blue, but we see it as blue because
• 35:16
  Speaker 1: it's reflecting blue light. And so the sun has some
• 35:19
  Speaker 1: of the blue removed, which makes it look a little
• 35:21
  Speaker 1: yellower to our eyes.
• 35:23
  Speaker 2: Oh that's so cool. And again yet another thing that
• 35:25
  Speaker 2: we had to account for to understand all of this stuff.
• 35:28
  Speaker 1: Amazing, And the reason the sun glows at this color
• 35:32
  Speaker 1: is because of its temperature. The surface of the Sun
• 35:34
  Speaker 1: is about five thousand kelvin and what we're seeing when
• 35:38
  Speaker 1: we look at the Sun is its surface, right. We
• 35:40
  Speaker 1: can't see through it. It's opaque. Another bit of popsight
• 35:42
  Speaker 1: you hear a lot is that it takes like thousands
• 35:44
  Speaker 1: of years for a photon to go from the center
• 35:47
  Speaker 1: of the Sun to the surface. And like, I don't
• 35:49
  Speaker 1: even know what that means, because you know what's happening
• 35:51
  Speaker 1: is photons are made at the center of the sun,
• 35:53
  Speaker 1: but the sun is opaque, so then they just get
• 35:55
  Speaker 1: reabsorbed and they contribute to the overall heat of the sun.
• 35:59
  Speaker 1: An individual photon doesn't go from the center of the
• 36:01
  Speaker 1: sun to the edge of the sun. It just heats
• 36:03
  Speaker 1: up the sun and the surface emits a new fresh photon.
• 36:06
  Speaker 2: Oh interesting, I mean I can't say that. You know,
• 36:09
  Speaker 2: Ada came home from the playground. It was like, did
• 36:11
  Speaker 2: you know that a photon at the center of the
• 36:13
  Speaker 2: sun takes you know, blah blah blah get to the edge.
• 36:15
  Speaker 2: I had never heard that before, but now I'm enlightened.
• 36:18
  Speaker 1: I hear that a lot. Okay, And so you can
• 36:21
  Speaker 1: mimic the same spectrum that the sun makes by heating
• 36:23
  Speaker 1: up like a piece of tungsten to the same temperature.
• 36:26
  Speaker 1: You have a five thousand degree filament of tungsten, it
• 36:29
  Speaker 1: will emit in the same spectrum as the sun. Right,
• 36:32
  Speaker 1: it's not one hundred percent true, because the Sun is
• 36:33
  Speaker 1: not a perfect black body radiator, right, It does reflect
• 36:37
  Speaker 1: some things, it's not a perfect absorber. So the peak
• 36:39
  Speaker 1: of the distribution for the Sun is actually in the
• 36:41
  Speaker 1: green spectrum. And so this is why you might hear
• 36:44
  Speaker 1: some popseye folks being like, did you know the sun
• 36:46
  Speaker 1: is actually green?
• 36:48
  Speaker 2: Okay? Well, so now let's take down that hypothetical. Did
• 36:51
  Speaker 2: you know the sun is actually green? Person?
• 36:54
  Speaker 1: So saying that that the sun peaks in the green
• 36:56
  Speaker 1: is actually saying, if you had a perfect black body
• 36:59
  Speaker 1: radiator at five thousand kelvin, it would peak in the green.
• 37:02
  Speaker 1: But we don't have a perfect black body radiator. Our
• 37:05
  Speaker 1: son actually peaks in the violet. And where it peaks
• 37:08
  Speaker 1: depends a little bit on how you're doing the accounting,
• 37:11
  Speaker 1: like are you doing it in wavelength? Are you doing
• 37:13
  Speaker 1: in frequency? These things have a non linear relationship, and
• 37:16
  Speaker 1: so there's some like calculus that goes on there, but
• 37:19
  Speaker 1: which gets accounted into which bin And so it's not
• 37:22
  Speaker 1: really even true saying that the sun peaks in the green,
• 37:25
  Speaker 1: and even if it peaks in the green, you would
• 37:26
  Speaker 1: still see it as white in space. It's not like
• 37:29
  Speaker 1: out in space the sun is green or violet or
• 37:31
  Speaker 1: any of these things. Really, it's just most accurately said
• 37:34
  Speaker 1: that there's a broad spectrum that if the sun were
• 37:37
  Speaker 1: a perfect black body radiator, would peak in the green,
• 37:39
  Speaker 1: but it isn't, so it peaks in.
• 37:41
  Speaker 2: The violet, which is my favorite color. So thank you, universe.
• 37:44
  Speaker 2: There we go.
• 37:45
  Speaker 1: Why don't I see it on your arm. Then why
• 37:47
  Speaker 1: aren't you painting your launcher room violet.
• 37:49
  Speaker 2: If we had been doing this podcast when I was
• 37:51
  Speaker 2: painting my bathroom, you would have seen my purple arm.
• 37:56
  Speaker 1: Well, I have purple on the wall behind me as well.
• 37:58
  Speaker 1: See I'm a big fan.
• 38:00
  Speaker 2: Oh it's a great color, best color, all right, So
• 38:02
  Speaker 2: tell me about how we get colors for some other stars.
• 38:04
  Speaker 1: Yeah, So we've learned that star color depends on its
• 38:08
  Speaker 1: temperature and on what its atmosphere is made out of
• 38:11
  Speaker 1: and its velocity. So most of the stars in the
• 38:14
  Speaker 1: universe are smaller than our star. The Sun is a
• 38:17
  Speaker 1: big star compared to the average star, which is more
• 38:19
  Speaker 1: like a red dwarf. So smaller stars have less gravitational pressure,
• 38:24
  Speaker 1: so they're not as hot, so they burn and they
• 38:27
  Speaker 1: glow in the red more than in the yellow. So
• 38:30
  Speaker 1: that's why they're called red dwarfs. Right, So smaller stars
• 38:33
  Speaker 1: burn cooler and slower, they're longer lived, and they tend
• 38:37
  Speaker 1: to be redder. So a lot of the stars out
• 38:39
  Speaker 1: there in the universe are cooler on their surface than
• 38:41
  Speaker 1: are a star, but there are some that are hotter.
• 38:43
  Speaker 1: Blue giants, for example, super enormous stars very hot on
• 38:47
  Speaker 1: their surface because of the crazy fusion happening at their core,
• 38:50
  Speaker 1: they tend to glow in the blue. So if you
• 38:52
  Speaker 1: look at the spectra of stars, you see a really
• 38:55
  Speaker 1: big range. They are fewer that are bluer because those
• 38:58
  Speaker 1: are bigger and burn brighter and burn out faster. Red
• 39:02
  Speaker 1: stars tend to burn a lot longer, like our star
• 39:05
  Speaker 1: is going to last billions of years. Really big huge
• 39:08
  Speaker 1: blue stars can sometimes only last millions, where as little
• 39:11
  Speaker 1: tiny red giants we think maybe can last hundreds of
• 39:15
  Speaker 1: billions or even longer, much longer than the age of
• 39:18
  Speaker 1: the universe. So we don't really even have a measure
• 39:20
  Speaker 1: for it.
• 39:21
  Speaker 2: Is there any relationship between the temperature which is star
• 39:26
  Speaker 2: burns and what we think its ability to sustain life is?
• 39:30
  Speaker 1: Yeah, great question. We have this one clue, right that
• 39:32
  Speaker 1: we have life around a yellow star and not a
• 39:34
  Speaker 1: red star. And does that mean that life only happens
• 39:37
  Speaker 1: around yellow stars or are we weird and unusual and
• 39:40
  Speaker 1: most of the aliens out there look up at a
• 39:42
  Speaker 1: red sun. Yeah, we don't know. Red stars tend to
• 39:45
  Speaker 1: be a little bit more variable sometimes, and so there's
• 39:48
  Speaker 1: arguments there, but it's all based on this an equals
• 39:50
  Speaker 1: one so until we meet the aliens, we won't know
• 39:53
  Speaker 1: the answer to those questions.
• 39:55
  Speaker 2: And I feel like if you could be at the
• 39:56
  Speaker 2: right spot next to a red star, that would give
• 39:58
  Speaker 2: you more time for life to pop up. But I
• 40:00
  Speaker 2: guess if it's more variable, not necessarily and it's colder,
• 40:02
  Speaker 2: and what does that do? And anyway, all right, yeah,
• 40:04
  Speaker 2: we need more data.
• 40:05
  Speaker 1: We definitely need more data. And what's in the star
• 40:08
  Speaker 1: definitely does have an impact, Like if there's magnesium in
• 40:11
  Speaker 1: the atmosphere, then those lines are removed from the star.
• 40:14
  Speaker 1: But that doesn't really change the star that you see
• 40:17
  Speaker 1: from the naked eye because you can't tell that individual
• 40:19
  Speaker 1: slice of the spectrum has been removed. It still looks
• 40:21
  Speaker 1: red to your eye. But if you pass these things
• 40:24
  Speaker 1: through a prism, you will notice that different stars, even
• 40:27
  Speaker 1: if they have the same temperature, have different spectrum because
• 40:30
  Speaker 1: they have different lines removed, and that tells you what
• 40:32
  Speaker 1: they're made out of. Most stars still totally hydrogen, like
• 40:36
  Speaker 1: the universe started out all hydrogen. Mostly still hydrogen, but
• 40:40
  Speaker 1: the elemental mixture does affect the lines in the atmosphere,
• 40:43
  Speaker 1: so it will affect the color of the star technically.
• 40:46
  Speaker 2: So we've talked about a lot of different things that
• 40:48
  Speaker 2: influence star color. When I look at at the stars
• 40:51
  Speaker 2: at night, Am I understanding correctly that the thing that
• 40:54
  Speaker 2: mostly determines the color I see is how hot they're burning?
• 40:57
  Speaker 1: Yeah, which is mostly determined by how big they are?
• 41:00
  Speaker 2: Okay?
• 41:01
  Speaker 1: So yeah, Redder stars are smaller and bluer stars are bigger.
• 41:05
  Speaker 2: Got it. I'll appreciate that so much more now.
• 41:08
  Speaker 1: And it's incredible what we can learn about these stars
• 41:11
  Speaker 1: just from the pattern of the light, or that we
• 41:13
  Speaker 1: even figured out that you can break up light into components,
• 41:15
  Speaker 1: and that it contains all of this useful information right
• 41:18
  Speaker 1: always makes me wonder what happened we yet figured out
• 41:21
  Speaker 1: what information is landing on the planet screaming itself, screaming
• 41:26
  Speaker 1: clues about the universe that we haven't yet figured out
• 41:28
  Speaker 1: that in a few hundred years people will be like,
• 41:30
  Speaker 1: oh my gosh, you guys were such idiots.
• 41:33
  Speaker 2: You know, I wonder the same thing in biology, What
• 41:36
  Speaker 2: are the things that we're missing that people will laugh
• 41:38
  Speaker 2: at us for in the future. But you know, all
• 41:39
  Speaker 2: you can do is take incremental steps forward and then
• 41:42
  Speaker 2: be willing to take those steps backwards when you learn
• 41:44
  Speaker 2: that you're wrong.
• 41:45
  Speaker 1: Yeah, and take things apart and try to learn about
• 41:47
  Speaker 1: them right exactly. Pass your parasites through a prism, See
• 41:51
  Speaker 1: what bits they're made out of.
• 41:52
  Speaker 2: Tell me what you find out, and everybody out.
• 41:55
  Speaker 1: There come up with your favorite color and your favorite parasite.
• 41:58
  Speaker 2: Ah, what's your favorite parasite? Daniel?
• 42:02
  Speaker 1: All the ones that are not in me?
• 42:04
  Speaker 2: Oh, that's a lot, that's a lot. You must really
• 42:06
  Speaker 2: like parasites.
• 42:08
  Speaker 1: I approve of their choice to not be inside me
• 42:10
  Speaker 1: right now.
• 42:10
  Speaker 2: Yes, well, you know, as we were telling a listener
• 42:12
  Speaker 2: the other day, they don't have a lot of choice.
• 42:14
  Speaker 2: But I'm glad that they're not in you.
• 42:17
  Speaker 1: And I hope that this has helped you appreciate the
• 42:19
  Speaker 1: beauty of the night sky. And next time you're out
• 42:21
  Speaker 1: camping or on a beach in Costa Rica protecting turtles
• 42:25
  Speaker 1: from raccoons, you'll appreciate that the night sky is colorful
• 42:29
  Speaker 1: and that those colors communicate information about the nature of
• 42:32
  Speaker 1: the universe, what's going on in the hearts of these big,
• 42:35
  Speaker 1: furious balls of fusion.
• 42:37
  Speaker 2: Enjoy the night sky. Friends. Daniel and Kelly's Extraordinary Universe
• 42:48
  Speaker 2: is produced by iHeartRadio. We would love to hear from
• 42:51
  Speaker 2: you we really would.
• 42:52
  Speaker 1: We want to know what questions you have about this
• 42:55
  Speaker 1: extraordinary universe.
• 42:57
  Speaker 2: We want to know your thoughts on recent shows, suggests
• 43:00
  Speaker 2: for future shows. If you contact us, we will get
• 43:03
  Speaker 2: back to you.
• 43:03
  Speaker 1: We really mean it. We answer every message. Email us
• 43:07
  Speaker 1: at Questions at Danielankelly.
• 43:09
  Speaker 2: Dot org, or you can find us on social media.
• 43:11
  Speaker 2: We have accounts on x, Instagram, Blue Sky and on
• 43:15
  Speaker 2: all of those platforms. You can find us at D
• 43:18
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• 43:19
  Speaker 1: Universe will be shy right to us