June 26, 2025 • 43 mins
Daniel and Kelly dive deep into the hearts of stars to explain why they all twinkle a little differently.
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Speaker 1 (00:06):
The best view in the universe is not from the
top of the Seer's Tower or the birds Dubai. It's
not from some seaside hotel. It's not from the top
of Mount Everest. It's from your backyard. On a dark night.
You can look up at the universe and see across
billions and billions of miles. Every view on Earth pales
(00:27):
in comparison to the vista you see across this ocean
of space. Though they are impossibly distant, you can still
see balls of gas furiously fusing, burning brilliantly enough that
they can be seen with your naked eyeball. And if
you look closely, you'll notice something incredible. There's a rainbow
of stars out there. White, blue, yellow, red. It's a
(00:49):
fabulously colorful universe. What does that mean? Why are stars
different colors? We'll be digging into the physics and countering
some usual pop sigh misinformation along the way. Welcome to
Daniel and Kelly's extraordinarily fabulous colorful Universe.
Speaker 2 (01:19):
Hello, my name is Kelly Windersmith. I study parasites and
space and I love looking at the night sky.
Speaker 1 (01:26):
Hi. I'm Daniel. I'm a particle physicist, and I don't
have a favorite color.
Speaker 2 (01:31):
I do. Mine's purple. Why don't you have a favorite color?
Speaker 1 (01:35):
I don't get the whole principle of choosing a favorite.
Like I like the colors, they're all nice. Why do
I have to pick one and say this one's my
favorite color? Like, I like purple, it's nice. I like orange. Yellow,
it's pretty good too. Blue is so soothing. I like
the colors. Grown do you have a favorite child?
Speaker 2 (01:52):
You know? You and Zach. I'll ask Zach what's your favorite?
Blah blah blah, and he's like, I don't see any
reason to pick a favorite. And I'm like, because people
use this as a conversation starter, and you're a conversation killer.
Speaker 1 (02:05):
I was just gonna say, it's the way people start conversations.
But it feels to me like dishonest, it's false. It's
like it's not what you really think or feel. It's
just like, oh, you like red, I like green. You
know it's not sincere, so it doesn't start a good conversation.
Speaker 2 (02:19):
I think it's implied that, like, you're not married to
that color for the rest of your life. I was
doing a book signing. I was like, oh, so tell
me something about you. And he's like, I hate small talk.
Speaker 1 (02:28):
And I was like, oh, okay, and that's the end
of this conversation.
Speaker 2 (02:33):
I did stop talking. I was like, okay, all right,
I don't know what else to say. Now you've ruined
the question I was planning on asking you today because
it involves the word favorite. But I was going to
ask you about your favorite or the best star viewing
experience you've had, Like when was the moment when the
sky was most clear and you could see the farthest.
Speaker 1 (02:50):
I think one of my favorite observing moments is not
actually looking at stars, because you know, stars are hard
to make out any features for because they're so far away.
They're sicly just points of light. But stuff in our
Solar system that you can actually see. And back in
the mid nineties, I was working on a project over
the summer right when comet shoemaker Levee was about to
(03:11):
slam into Jupiter, and I had access to a super
high speed camera and so we pointed it at Jupiter
hoping to catch really high speed photographs of the impact
to see like, you know, planet sized plumes of fire
emerging from it. It was super cool.
Speaker 2 (03:27):
I mean, I do feel like I asked you something
like what's your favorite color? And you answered macaroni and cheese.
But that is a very cool story. Did you see
what you wanted to see?
Speaker 1 (03:36):
Yeah, we got to see shoemaker levee impact on Jupiter.
Unfortunately impacted around the back of Jupiter, so we didn't
see the collision itself, but we did see the plume
coming up over the limb of Jupiter. Really pretty amazing.
I sort of remember it in black and white. I
can't really answer your color questions, but Jupiter does have
a lot of beautiful colors. See, it doesn't just pick.
Speaker 2 (03:55):
One that's amazing. And you keep sort of wiggling around
my questions. That's fine, that's fine. What you're saying is interesting,
so it's fine for content.
Speaker 1 (04:04):
And i'd ask you what your favorite color is, But
you're wearing a color right now. You literally have paint
all over your arms. That's your favorite color.
Speaker 2 (04:11):
Well, that's my favorite color for my laundry room renovation
that I'm working on right now. But my favorite star
viewing moment I got really lucky one. So I was
in Costa Rica and I was in a community where
there was a big leather back sea turtle conservation project
going on, and leather back sea turtles can get distracted
by lights and then they move towards those lights and
then they don't go out to the ocean after they
(04:33):
hatch like they're supposed to. So the whole community had
very dim red lights and they turned off all of
their bright lights at night, and so we were sort
of in the middle of nowhere and all the lights
were off. So my job at two am was to
guard the hatchery so that raccoons wouldn't dig up the
leather back sea turtle eggs and eat them.
Speaker 1 (04:50):
Wow.
Speaker 2 (04:50):
So it was like two am in Costa Rica. It
was the middle of nowhere. All the lights were out,
and it was just the most amazing view of the
Milky Way and you know, shootings stars and at any
time there could be baby turtles. Like that's Pete Kelly
life right there. I'd much rather spend time with my kids,
But that was amazing.
Speaker 1 (05:08):
That sounds like a magical moment. Did the night sky
look anything like your outfit does right now?
Speaker 2 (05:13):
Yeah, except a fewer holes in it. This is also
what I wear. What I'm doing some renovation work. I
don't know, it's comfy.
Speaker 1 (05:19):
For the audio only listeners. Kelly's wearing something which looks
like it has star patterns on it.
Speaker 2 (05:24):
It does. And my daughter has a matching outfit that
we wear sometimes, and she still wants to wear even
though this dress has holes in it. Whenever she wants
to wear a matching outfit, I am all in because
I imagine it's like weeks or months before she's too
old to want to do that. So every day it's
an automatic.
Speaker 1 (05:39):
Yes, You've got to savor those moments when the kids
still want to spend time with you, because pretty soon
they're going to grow up and move on.
Speaker 2 (05:46):
I know, I know your kid's going to college.
Speaker 1 (05:50):
And kids are not the only thing growing up and
changing and moving on. Everything in the universe is going
through its own life cycle, including the stars in the sky,
burning and glowing and changing colors as they do.
Speaker 2 (06:02):
Yeah. So when I was listening to your introduction, I
was realizing that I don't appreciate all the colors of
the stars in the sky. I just think of them
as white and sort of look at them as sort
of a blurry something. I don't pay attention to the
individual colors, the palette of the universe. So I'm excited
that next time I look at the night sky, I'll
(06:22):
pay a little bit more attention, and I'm excited to
learn more from you today.
Speaker 1 (06:25):
Yeah, the universe is very colorful, but it's not just
to please you or to start conversation among two am
sky watchers who can otherwise talk to each other. It's
for physics reasons, and the colors in the night sky
are going to tell us a lot about what's going
on inside those.
Speaker 2 (06:41):
Stars, as long as it's not for chemistry reasons.
Speaker 1 (06:46):
So this is actually part one of a two part
series about why stars have colors and what it tells
us about the universe, which ends up with a really
interesting story about yet another overlooked female astronomer.
Speaker 2 (06:58):
Oh I love when I'm surprise. While we're recording, I
didn't realize this was a two parter.
Speaker 1 (07:04):
I just realized as the two parter because I'm preparing
that other episode, and now I'm understanding, Oh my gosh,
this is the perfect setup for that episode. So good
job Daniel realizing that in real time.
Speaker 2 (07:14):
Welcome to Star Week.
Speaker 1 (07:17):
This is how carefully we plan the episodes on the podcast.
All right, So before we dig deeper, I was curious
if people knew why stars had different colors, and so,
as usual, I went out to our group of wonderful, clever, hilarious,
well informed, good looking volunteers to ask them if you
would like to join their ranks for future episodes. Please
(07:38):
don't be shy, right to us two questions at Danielankelly
dot org. We'll hook you up in the meantime, think
about it for yourself. Do you know why stars are
different colors? Here's what our volunteers had to say. We
know the color here on Earth is based on different
wavelengths of light, so I'm assuming that the same principles
(08:00):
apply to stars.
Speaker 3 (08:02):
Red shift the including distance from and speed away from
the observer.
Speaker 4 (08:06):
Color of the stars related to its size. So the
older the stars, the more it's been able to fuse,
the heavier elements you get different.
Speaker 1 (08:13):
Spectrum their temperature and the element.
Speaker 5 (08:18):
I know that big hot stars are described as below
and small coola stars described as red, and middlely ones
like our sun are yellow.
Speaker 4 (08:29):
Well, I think the color of stars depends pretty well
solely on their age.
Speaker 3 (08:35):
I think stars are different colors based on the levels
of hydrogen and helium in the star.
Speaker 4 (08:39):
Red ones are shy, and as they get closer they
turn red.
Speaker 1 (08:42):
Blue ones are kind of cool, so they're going away
from you. They don't care.
Speaker 2 (08:47):
Different elements of different colors, and stars throughout their life
fuses loads of different elements.
Speaker 1 (08:54):
I think stars are different colors because of the gases
that are in them, and also because of the temperature
of the star.
Speaker 4 (09:01):
Probably due to their composition, different elements they are made
up of, and perhaps also their size and perhaps just
how they're burning their energy output.
Speaker 1 (09:11):
Also, the universe believes in diversity, equity inclusion, and that's
why they're different colors.
Speaker 2 (09:16):
The temperatures are different and that causes the black body
radiation peaks to be at different wavelength.
Speaker 4 (09:21):
Stars are different colors because they have different elements and
they burn at different temperatures, which changes the color we see.
I'm really not sure where the stars are different colors,
but if I had to guess, I would say it
had to do something with where they were at in
their life cycle and the gases that they are made
up of.
Speaker 3 (09:41):
I think stars are different colors because the way they
expand and like the gases inside of them like as
they expand and get hotter, I think they like change
colors and stay those colors their lifetime.
Speaker 1 (09:55):
I would think that stars are different colors because they
emit different light particles, but I think a nonscience the
answer would be that they have a cool aura.
Speaker 2 (10:05):
Amazing answers I chuckled, and some really clever insights here.
What did you think, Daniel?
Speaker 1 (10:10):
I think there's a lot of interesting stuff going on here.
The picture I'm putting together of what people imagine causes
the different colors of stars is that this different fusion
happening with like different ingredients. Maybe you have more metal
here and more metal there, and that's somehow changing what's
going on, and that's changing the burning of the star
the way you can put copper in a Bunsen burner
(10:31):
and it turns green, for example.
Speaker 2 (10:33):
That is my understanding coming into this conversation is that
I do think it depends on what elements are getting
burned and how hot. But often I'm wrong.
Speaker 1 (10:43):
So I suspect a lot of you listening out there
probably think the same thing, which is why we do
this segment to orient us and understand where we need
to take you from your current understanding to a deeper,
more physical understanding. So we hope that by the end
of the episode you have a deeper view of why
stars have different colors, because the answer is a little
bit more subtle than anything we heard from our volunteers.
Speaker 2 (11:03):
All Right, I love it. Let's dig in and let's
start with the basics. Tell me about light and color.
Speaker 1 (11:08):
Right, So some of the listeners commented that different colors
mean different wavelengths, and that's true. Of course we're interested
in like why is flight emitted at different wavelengths? But
fundamentally it's important to understand the physical mechanism here, like
why are we seeing different colors? And they're right, because
light is electromagnetic radiation. The universe is filled with electromagnetic field,
and that field can ripple, and when electrons in alpha
(11:30):
centauri wiggle, they cause ripples in that field because electrons
are connected to that field. Right, When electron moves, it
wiggles that field, and that wiggle is what we see
as photons, for example. And those wiggles have frequencies, and
the frequencies correspond to different wavelengths, and those wavelengths correspond
to colors.
Speaker 2 (11:50):
I feel like a bunch of pieces actually just click
together in my head that should have clicked together much earlier,
but there they are, okay.
Speaker 1 (11:57):
Click And the same mechanism is like how radio works
wizer an antenna because electrons are going up and down
in the antenna, and as they do so, they make
the photon field wiggle just the same way, like if
you're holding the end of a jump rope and you
go up and down, you make wiggles down the jump rope.
It's exactly the same mechanism.
Speaker 2 (12:14):
I think the piece is just unclicked. Oh no, I
think I don't understand the electrons going up and down
the antenna. Thing is it just radio waves are traveling
through the antenna and that's radio frequencies.
Speaker 1 (12:26):
Well, an electron has an electric field around it, right,
If the electron just sits there, the electric field doesn't change.
What happens if the electron moves up, well, the electric
field also has to move up. Or if the electron
field moves up and then down, the electric field moves
up and then down. But it doesn't do so instantly,
Like if you wiggle an electron in an antenna that's
a mile away from me, I don't instantly see it
(12:47):
change in the electric field. It has to propagate and
So if the electron is going constantly up and down
and up and down, then it's making waves up and
down in the electric field that propagate out away from it.
And if I'm a mile away and i have electrons
in my antenna, those wiggles in the electric field are
going to push on my antenna's electrons, which are going
to go up and down, and then I'm going to
read that out as current. So yeah, the electrons in
(13:10):
descending antenna wiggle the electric field, which wiggles. Electrons in
the receiving antenna, which move and can be picked up
by my electronics can be reclick yep, yah yah. And
so the different colors are different wavelengths of those wiggles.
Photons are wiggles in the electromagnetic field, but they can
have different wavelengths. Right. They can be really really narrow,
(13:32):
so they're like very high frequency, like ultraviolet or purple.
They can be really really long, so they're like radio
waves or red light or infrared light. And there's a
potential source of confusion here. Remember these things are quantum mechanicals,
So photons are discrete units. Like you can have one
photon or two photons, but you can't have two point
seven eighty one photons, but you can have photons of
(13:54):
any energy. That's a continuous spectrum, So there's an infinite
number of frequencies on the spectrum.
Speaker 2 (14:01):
So does that mean there's an infinite number of colors?
Speaker 1 (14:04):
Mmmm, yes, great question. Right, So there are an infinite
number of frequency choices for a photon. But colors are
things that we experience in our mind. Right. There are
responds to signals on the optic nerve. So let's talk
momentarily about the physics of the biology of what's going
on there. You have photons that enter your eyeball and
they hit the back of the eyeball and the back
(14:25):
of the eyeball, there are three different kinds of cells
that respond to different colors. They have proteins on them
that operate like little switches, and when they absorb a
photon of the right color, they flip that switch and
they send a signal up the optic nerve. This whole
continuous spectrum of photons gets converted into three numbers, how
much did you turn on cone one, Cone two, and
(14:45):
cone three? And then your brain interprets those and generates
the experience of the color. So the color is actually
in your mind. It's not on the photon, right, we
say red photon or green photon when we're being sloppy,
but really the boon has an energy and the experience
of color is only in your brain.
Speaker 2 (15:03):
And we got a great question on our discord channel,
which you can join by going over to Danielankelly dot
org and clicking the invite and Quicksilver the DIRG Sorr
who was the discord quicksilver the DIRG anyway, this individual
going by the moniker Quicksilver, the DIRG wanted to know
something about why we see the colors that we do see.
(15:26):
And actually, our distant ancestors had two kinds of light
cones and we have three, and so why do we
see the colors that we see. The answer, really, at
the end of the day is we're not one hundred
percent sure, but we think what happens is that there
was a gene duplication event, and these happens every once
in a while in our genome. And so now instead
of having two different kinds of cones, you had two
(15:48):
different kinds of cones, but three different genes for those cones,
and over time selection tinkered with that extra new gene
and we ended up with the ability to see the
color red. Already see things like green, and the thought
was that seeing colors like red allowed our primate ancestors
to differentiate between different kinds of fruits and in particular
(16:09):
whether or not the fruits were ripe. And there are
some macaques that only have two types of cones and
some macaques that have three types of cones in the
same species, there's this variability. Some studies have found that
if you have three types of cones, you get ripe
fruits quicker and eat them quicker, which shows a benefit.
But other studies and other kinds of macaques haven't found
that because it's biology, so it depends depends there you go.
Speaker 1 (16:32):
And I think you put your finger on it, because
the important thing here is the ability to distinguish different colors, right,
But I think that depends not just on like the
number of different kinds of cones you have, but also
the processing power behind it. I know that like mantis,
shrimp are famous for having like more than ten different
kinds of cones, but they actually apparently are terrible at
distinguishing different colors because they have almost no neural processing
(16:55):
behind it. I think they might just like experience ten
different literal colors. We have a huge number of different
colors that we can distinguish because we can do this interpolation, right,
That's what your brain is doing is it's getting like, oh,
a little bit from the bluish cone, a little bit
from the reddish cone, a little bit from the greenish cone,
and it's saying, okay, what color would give me this
(17:15):
pattern and then sort of inferring what color might be there.
But again, the experience of color, the reason like red
is reddish and blue is bluish has nothing to do
with the photon. That's something your brain has assigned to
it has invented, has fabricated. Right in principle, it could
make up a new color. If you've got a new
cone and planted that was sensitive to the ultraviolet, that
your brain could invent a new experience, not one that's
(17:38):
a combination of the other ones, but like a real
novel experience to represent the signal from the UV cone.
Speaker 2 (17:44):
And there are insects that can see in the UV.
And it makes me so sad when I look at
a beautiful flower and think there's layers that I'm missing.
But anyway, I'm guessing based on our examples that you
and I both read An Immense World by Ed Young,
because we both seem to have cherry picked examples from
that fantastic book.
Speaker 1 (18:01):
It is definitely a great book, a lot of fun,
and recommend everybody read that, especially if you're interested in
physics and biology, because it covers both of those topics
about our experience.
Speaker 2 (18:09):
Okay, so the three kind of cones that we have
determine what colors we can see in the night sky.
Are we missing a lot or are there ultraviolet stars
out there that we're missing.
Speaker 1 (18:20):
We're definitely missing a lot because we can only see
a certain range of photons ultraviolet and infrared. Everything below
that and everything above that we can't see, and the
sky definitely is bright in those colors. That's why, for example,
we have radio telescopes and infrared telescopes and ultraviolet telescopes
because stars and other different phenomena emit differently in those
spectrum and if you can see those, you can see
(18:41):
different kinds of things. Also, the universe is transparent differently
in different frequencies. Some frequencies of life can go through
dust clouds and others can't, and so if you want
to see through dust clouds, you've got to change your frequency.
So absolutely the night sky looks very different outside the
visible range our star, and of course peaks right in
the center of the visible range, which again is no coincidence. Right.
(19:05):
If you're going to evolve vision, you might as well
evolve it to be able to see the most common
photons that are around you. So if we had evolved
around a redder star, for example, probably our visible range
would be lower. The Sun is an unusual star. Most
of the stars out there are redder than our star.
Our star is yellower than most stars out there, so
we may have a different visual range than most of
(19:26):
the aliens.
Speaker 2 (19:27):
So are you postulating that the color of the star
determines the colors that we see, because I feel like
that's not an evolutionary argument that I understand. Does the
color of our star impact the color of things on
Earth that are important for food, mating or running away
from a predator?
Speaker 1 (19:43):
I think it makes sense for us to be most
sensitive to the photons that are most present here on
Earth for that range. Whether we can experience two or
seven or three or whatever, I think is a different question.
But for us to be sensitive to the most common
kind of photons makes sense to me. I'll give you
that you're skeptical. Why A you're skeptical?
Speaker 2 (20:02):
So I totally follow the argument that the most common
kinds of photons in the environment would be the ones
that were good to sense. But if for some reason
those didn't translate into an increased ability to find your
food or an increased ability to recognize a mate, then
I don't necessarily think that selection would hone in on those.
And there's so much variability and what animals can see.
(20:24):
You know, there's plenty of dichromates, so they don't have
three kinds of cones and they get along just fine.
So yeah, how do you explain the variability?
Speaker 1 (20:32):
Then that's a great point. And I can give you
an example to support your point, which is neutrinos. Neutrinos
are everywhere in our environment, but pretty much useless because
everything is transparent to them, and so it wouldn't be
great to develop a neutrino eyeball even though they're everywhere.
So you're right, just being ubiquitous isn't enough to have
to be useful. And so I think the combination of
(20:53):
the fact that they are everywhere, and stuff on Earth
tends to not be transparent to them, makes them useful
for us to see things. So I think you're right.
It's more complicated than just the physics of this region
has to also be like useful in your environment. For sure.
I have no idea why you would have two or
seven cones.
Speaker 2 (21:11):
I guess both of our fields are useful. You ponder
the question Daniel and I were just debating during the break,
And when we get back, we'll talk about why stars
have different colors? All right, and we're back. You look
(21:39):
up at the night sky and there are lots of
different colors of stars. Though I'll be honest, I missed
that in the past. I'm gonna be paying much more
attention now. So Daniel, why do those stars have different colors?
Speaker 1 (21:50):
So there's sort of three big factors that control what
color a star is in our sky. One is what
it's made out of, another one is its temperature, and
the last one is its velocity. So let's do those
in order. What it's made out of. This is the
one that's connected to your experience of like putting copper
in a Bunsen burner and seeing it glow green. That's
(22:10):
because atoms are quantum mechanical little objects and they have
energy levels. You know, electrons around an atom can't just
be at any energy willy nilly. There's a ladder of
energies there, and because there's a ladder of energies there,
they can only eat and emit photons of certain energies,
the ones that let them go up or down the ladder.
So when an electron is around an atom and a
(22:30):
photon comes by, if that photon has just the right
energy to take it up one or two or seven
rungs on that ladder, it can eat that photon. You
might think I don't care about what photons the electron eats,
but actually does matter what it absorbs and what it reflects,
because what it reflects is what you see. Right, If
you're looking at something that's blue, it's not blue because
(22:50):
it's eating blue photons. It's blue because it's eating everything
but the blue photons. It's reflecting blue photons back at you.
Remember you see something blue because some light in the
blue range has hit your eyeball and you responded to that.
So it's important what energy levels an atom can absorb.
And the same is true also in the reverse, Adam's
(23:11):
in midlight. That's what's happening to the copper in your
Bunsen burner. It's getting hot, and the inverse process is happening.
An electron jumps down energy levels and gives off a photon,
a green photon in the case of copper.
Speaker 2 (23:22):
That always felt very counterintuitive to me, that the color
that I'm seeing is the color that's being given off
by something. It almost feels like everything is disguising itself
in some way. I don't I don't know why my
brain ahead trouble wrapping itself around that.
Speaker 1 (23:36):
I totally remember the first time I understood that. I
was like nine, and I was like, oh my gosh,
things that are blue are not actually blue, they just
look blue. And then I realized, well, maybe that's what
it means to be blue, to look blue. But yeah,
I had the sense that like, if I could see
through these photons to what things actually looked like, I
could perceive a deeper truth to the universe. But the
(23:56):
universe is kind of a construct we've assembled in our
head from our experience of it, and there's a lot
of that that's imagined, that's put together from our experience
and the way we paint these colors on things is
just one layer of that.
Speaker 2 (24:08):
Yeah, man, Yeah, I totally agree though.
Speaker 1 (24:15):
Yeah, but that's the joy physics. It helps you separate
what's really out there and what you know about it,
which you don't know about it, which parts you're building
in your mind. Super fascinating, even if it is philosophical
and could never be understood. So the next piece to
understand is why things have different colors? Right, We said
that atoms have energy levels, and electrons can jump up
energy levels eating photons or down energy levels emitting photons,
(24:38):
and those photons have specific energies corresponding to those gaps. Well,
different atoms have different energy levels. Copper and mercury and
helium and hydrogen all have different energy levels. Because the
solutions to the Shorteninger equation are different, you got different
numbers of protons, and the whole configuration of the atom
is different. Every atom has its own unique ladder, which
means that they have like a fingerp If you take
(25:01):
an element and you take a gas of it and
heat it up, and then you take the light from
that pass it through a prism to spread it out,
you'll see that Each element has its own unique fingerprint,
its own spectrum. They'll have these little bands like a
blue one and a red one, or a different element
will have like a green band and the blue band
will be shifted over. So you can tell what something
(25:21):
is made out of just by looking at a spectrum
of a hot gas. So there's two things that are
happening here. You have hot gas, it glows in certain colors, right,
And if you have more oxygen, you glow in these colors.
You have more neon, you glow in those colors. And
our whole next episode is going to be about using
spectroscopy to understand what stars are made out of. But
this also absorption, Right, if a star has an atmosphere
(25:42):
and that atmosphere is mostly neon, for example, then it's
going to absorb that light. So if you have a
hot blob of gas, it emits light to those frequencies.
If you have light that passes through an atmosphere, then
it absorbs those frequencies.
Speaker 2 (25:57):
So it feels to me now like we have an
infinite number of combinations of elements that could be emitting
and like gases that could be absorbing. How do we
make sense of the output given that there's now so
many different options, and it's probably not just one element
that's emitting at a time. There's probably a couple different
things that are emitting. And I'm overwhelmed.
Speaker 1 (26:16):
Yes, it is overwhelming. It's a hard problem, and it
was solved by a very clever young lady around the
turn of the century. And we're going to talk about
that in the next episode. Okay, but even if you
mix all these elements together, what you get are a
bunch of different spikes Like these are narrow emission lines.
You can't put them together to get a broad spectrum.
And that's not what most of the light from the
stars is. This is like people's conception, but most of
(26:37):
the light from the star comes from a completely different process.
It's not from atomic emission and absorption. It comes from
the plasma inside the star just glowing at a certain temperature.
Speaker 2 (26:48):
What all right, we were all wrong, audience and friends
of mine. Okay, so Daniel, let's move on to the
next thing. Then tell us more about this thing that
actually contributes most of the color.
Speaker 1 (26:57):
Yeah, so we said that the color of stars comes
from what they're made out of, and that has to
do with atomic absorption, and emission mostly in the atmosphere
of stars, but also from its temperature. And so that's
what we're going to dig into next. And there's a
process here that has a terrible, absolutely, terrible, very misleading name.
It's called black body radiation that describes why stars glow
at certain temperatures. And it's terribly the name because a
(27:19):
star doesn't seem like a black body. Right.
Speaker 2 (27:22):
Nope, you guys did it again.
Speaker 1 (27:23):
But in physics, we have a model of some hypothetical
object with no reflection, Like any photon you shoot at
it, it will absorb it and just like heat up. And
even in the hypothetical version, it's not black. It just
means that it doesn't reflect. It glows because of its temperature.
Everything in the universe that has a temperature and is
made of charged particles will glow. Like if you have
(27:43):
fluorescent lights in your ceiling, you look up that has
a hot gas in it that's glowing because of its temperature.
Or you're glowing right now, Kelly, because of your temperature.
Not in the visible light, but if I put on
night vision goggles or infrared goggles, I would be able
to see you emitting light.
Speaker 2 (28:00):
What is the physics definition of glow is it just
releasing photons or something.
Speaker 1 (28:04):
It's just releasing photons because you have charge particles in you,
and charge particles are always interacting and moving around and whizzing,
and when they do so, they emit photons. Like an
electron can't change directions without emitting a photon. That's how
it does it. And an electron is flying to the
universe and it wants to curve along a magnetic fields
or something, it's got to push out a photon in
(28:24):
the other direction to conserve momentum. Now you have a
big blob of gas with all sorts of charge particles
whizzing around, they're going to be constantly emitting photons, and
they emit a very broad spectrum. Not like the atoms
we talked about, we have very specific energy levels. This
black body radiation is a very broad spectrum, but it
has a peak that depends on the temperature. So really
cold things tend to emit in the infrared. Warmer things
(28:47):
emit invisible. So for example, you take a piece of metal,
it's glowing right now, even if it's cold, just in
the infrared. You can't see it. Put in the oven,
heated up, put it in the forge. It starts to
glow red, and then it glows white. Right. White? Hot
is very hot? Why because now it's hot enough to
be glowing in the visible Keep heating it up. It'll
start to glow in the ultra violet. You won't see
(29:09):
it anymore, but it be super duper hot. The temperature
of something determines the peak of its emission, right, So
everything in the universe that's made of charge particles glows
at a certain temperature, and that temperature controls the frequency
of the emission.
Speaker 2 (29:23):
Okay, all right, a few questions. So when an electron
kicks out a photon, is it still an electron?
Speaker 1 (29:28):
It's still an electron because a photon is neutral. Yeah.
Speaker 2 (29:30):
How many photons can an electron kick out? Can I
just do that all the time?
Speaker 1 (29:36):
Oh my gosh, what an amazing question. It makes me
think of an electron as like having a bag of
photons that they could run out of, right, like fuel
You think of like rockets, right, and they need some source. No,
an electron has an infinite number of photons. Remember, these
are just wiggles in the electromagnetic field, right, And so
it's not like it's kicking off some substance. But in
(29:57):
order to conserve momentum, you have to have some momentum
move to the ectromagnetic field and some momentum moves through
the electron field.
Speaker 2 (30:03):
Wow, okay, all right. So say you've got some iron,
and we talked about iron having emission line spectrums where
the electrons get excited and they jump to different levels
and they emit light and then you hate that iron
up and now it's glowing. Are you saying that the
glow is more important than the jumping of the levels.
Speaker 1 (30:28):
The most general answer is that it depends on what
it's made out of and its temperature, and in the
case of stars, it's mostly black body radiation. Like when
we look at the spectrum from the Sun, it's almost
all black body radiation. So that's definitely the most important effect.
And there's a combination of the two things. So you
have the star which is glowing very broad spectrum which
(30:48):
peaks right in the middle of our visual spectrum for
our star. But then the sun has an atmosphere, and
this atmosphere is gas and it's made out of various stuff,
and that atmosphere will eat that spectrum. So the light
we get from the Sun is a huge black body
peak with a few lines removed. That's absorption spectrum. So
if you look at the spectrum from the sun, you
(31:09):
see reds and yellows and greens and blues, but then
you see these black spots, these things that have been removed.
That tells you what's in the atmosphere of the Sun.
You can see the hydrogen lines have been removed, the
sodium lines, the helium lines, the magnesium lines, and so
that helps you figure out what's in the atmosphere of
the Sun. So the two things happening there is the
broad glow inside the sun, which we're not fully seeing
because parts of it have been removed as the Sun's
(31:32):
atmosphere eats some of those frequencies.
Speaker 2 (31:35):
That's amazing.
Speaker 1 (31:36):
Yeah, and so the last piece we talked about for
what determines the light that comes from a star is
the velocity. And a bunch of listeners pointed this out
that things that are moving away from you will be
red shifted, just like a police siren moving away from
you will have a lower sound than a police siren
moving towards you. It's just a Doppler effect. And so
as star emitting light as it moves away from you
is going to get red shifted, and we use this
(31:57):
red shift to measure that velocity. It's like a huge
the important thing in astronomy. A star moving towards you
would be blue shifted, and we can tell the red
shift in the blue shift because we know the typical fingerprints.
Like you get a star you've never seen before and
you want to measure its red shift. Well, you might think, well,
how it I know it's impossible. If the star has
hydrogen lines but they're shifted by a few nanometers, and
(32:19):
it has magnesium lines and those are shifted by the
same number of nanometers, then the most likely scenario is, oh,
this isn't made of some new super weird metal that
looks like magnesium and hydrogen but shifted. It's just magnesium
and hydrogen and it's been shifted due to the red shift.
So you can fit these lines, these specter, these absorption
and emission lines, to tell you the frequency shift of
(32:40):
an individual star. And so that definitely affects the color
of the star in the sky. And almost everything in
the sky is moving away from us, so they're all
red shifted.
Speaker 2 (32:50):
I'm having one of those moments where I'm just so
proud of our species for figuring all of this out,
Like that's so many different things to keep track of.
It's so incredible that we got there and that we
understand all of this stuff and anyway way to go humans.
Speaker 1 (33:03):
This is the amazing thing about astronomy is that you
cannot leave the Earth. Mostly you've got to figure out
the puzzle of the universe from these clues. And we
didn't assemble this experiment in this way. We stumbled over
these things. People had moments of insight where they realized,
hold on a second, this pattern actually reveals this thing
about the universe. Those are incredible realizations, so powerful. And
(33:25):
let me just qualify what I said a moment ago
about everything moving away from us. Galaxies are moving away
from us, and those are all red shifted. Most of
the stars in the Milky Way are held together by
the gravity of the Milky Way, and so those aren't
red shifted and moving away from us. The stars in
the night sky are the ones from the Milky Way.
Those are the ones we can see. They're not red shifted.
But other galaxies are red shifted.
Speaker 2 (33:46):
All right, Well, that is amazing. Let's take a break,
and when we get back, we're going to talk about
the color of our very own sun. All Right, we're back,
(34:10):
and Daniel wants to tell us about why Niel de
grass Tyson is wrong.
Speaker 1 (34:14):
I don't want to say that. I do want to
dismantle a lot of pop sign myths that you.
Speaker 2 (34:19):
Hear from Neil de grass Tyson.
Speaker 1 (34:22):
I didn't say that. I didn't say that. I just
want to say that, you know, on this podcast, we'd
like to dig deep, well past the usual pop side
explanations and tell you what's really going on. So you know,
we're interested in the colors of the stars in general.
But of course our sun is near and dear to
our hearts. Why does the sun have its particular color?
And the Sun's color is actually fascinating because if you
(34:42):
were out in space and you were looking at the sun,
it's white, right, And what does it mean for the
sun to be white? White isn't like a color. It's
a mixture of the colors, and it's sort of the
way your brain responds when you see a very broad
spectrum of light across the visible range. So out of space,
the sun is white. Here on Earth because of the
effects of the atmosphere. The sun looks a little yellower, right,
(35:05):
because the atmosphere tends to scatter blue light, which is
why the sky, which doesn't have its color of its own,
looks blue, right, because it's reflecting blue light. Air itself
is not blue, but we see it as blue because
it's reflecting blue light. And so the sun has some
of the blue removed, which makes it look a little
yellower to our eyes.
Speaker 2 (35:23):
Oh that's so cool. And again yet another thing that
we had to account for to understand all of this stuff.
Speaker 1 (35:28):
Amazing, And the reason the sun glows at this color
is because of its temperature. The surface of the Sun
is about five thousand kelvin and what we're seeing when
we look at the Sun is its surface, right. We
can't see through it. It's opaque. Another bit of popsight
you hear a lot is that it takes like thousands
of years for a photon to go from the center
of the Sun to the surface. And like, I don't
(35:49):
even know what that means, because you know what's happening
is photons are made at the center of the sun,
but the sun is opaque, so then they just get
reabsorbed and they contribute to the overall heat of the sun.
An individual photon doesn't go from the center of the
sun to the edge of the sun. It just heats
up the sun and the surface emits a new fresh photon.
Speaker 2 (36:06):
Oh interesting, I mean I can't say that. You know,
Ada came home from the playground. It was like, did
you know that a photon at the center of the
sun takes you know, blah blah blah get to the edge.
I had never heard that before, but now I'm enlightened.
Speaker 1 (36:18):
I hear that a lot. Okay, And so you can
mimic the same spectrum that the sun makes by heating
up like a piece of tungsten to the same temperature.
You have a five thousand degree filament of tungsten, it
will emit in the same spectrum as the sun. Right,
it's not one hundred percent true, because the Sun is
not a perfect black body radiator, right, It does reflect
some things, it's not a perfect absorber. So the peak
(36:39):
of the distribution for the Sun is actually in the
green spectrum. And so this is why you might hear
some popseye folks being like, did you know the sun
is actually green?
Speaker 2 (36:48):
Okay? Well, so now let's take down that hypothetical. Did
you know the sun is actually green? Person?
Speaker 1 (36:54):
So saying that that the sun peaks in the green
is actually saying, if you had a perfect black body
radiator at five thousand kelvin, it would peak in the green.
But we don't have a perfect black body radiator. Our
son actually peaks in the violet. And where it peaks
depends a little bit on how you're doing the accounting,
like are you doing it in wavelength? Are you doing
in frequency? These things have a non linear relationship, and
(37:16):
so there's some like calculus that goes on there, but
which gets accounted into which bin And so it's not
really even true saying that the sun peaks in the green,
and even if it peaks in the green, you would
still see it as white in space. It's not like
out in space the sun is green or violet or
any of these things. Really, it's just most accurately said
that there's a broad spectrum that if the sun were
(37:37):
a perfect black body radiator, would peak in the green,
but it isn't, so it peaks in.
Speaker 2 (37:41):
The violet, which is my favorite color. So thank you, universe.
There we go.
Speaker 1 (37:45):
Why don't I see it on your arm. Then why
aren't you painting your launcher room violet.
Speaker 2 (37:49):
If we had been doing this podcast when I was
painting my bathroom, you would have seen my purple arm.
Speaker 1 (37:56):
Well, I have purple on the wall behind me as well.
See I'm a big fan.
Speaker 2 (38:00):
Oh it's a great color, best color, all right, So
tell me about how we get colors for some other stars.
Speaker 1 (38:04):
Yeah, So we've learned that star color depends on its
temperature and on what its atmosphere is made out of
and its velocity. So most of the stars in the
universe are smaller than our star. The Sun is a
big star compared to the average star, which is more
like a red dwarf. So smaller stars have less gravitational pressure,
so they're not as hot, so they burn and they
(38:27):
glow in the red more than in the yellow. So
that's why they're called red dwarfs. Right, So smaller stars
burn cooler and slower, they're longer lived, and they tend
to be redder. So a lot of the stars out
there in the universe are cooler on their surface than
are a star, but there are some that are hotter.
Blue giants, for example, super enormous stars very hot on
(38:47):
their surface because of the crazy fusion happening at their core,
they tend to glow in the blue. So if you
look at the spectra of stars, you see a really
big range. They are fewer that are bluer because those
are bigger and burn brighter and burn out faster. Red
stars tend to burn a lot longer, like our star
is going to last billions of years. Really big huge
(39:08):
blue stars can sometimes only last millions, where as little
tiny red giants we think maybe can last hundreds of
billions or even longer, much longer than the age of
the universe. So we don't really even have a measure
for it.
Speaker 2 (39:21):
Is there any relationship between the temperature which is star
burns and what we think its ability to sustain life is?
Speaker 1 (39:30):
Yeah, great question. We have this one clue, right that
we have life around a yellow star and not a
red star. And does that mean that life only happens
around yellow stars or are we weird and unusual and
most of the aliens out there look up at a
red sun. Yeah, we don't know. Red stars tend to
be a little bit more variable sometimes, and so there's
arguments there, but it's all based on this an equals
(39:50):
one so until we meet the aliens, we won't know
the answer to those questions.
Speaker 2 (39:55):
And I feel like if you could be at the
right spot next to a red star, that would give
you more time for life to pop up. But I
guess if it's more variable, not necessarily and it's colder,
and what does that do? And anyway, all right, yeah,
we need more data.
Speaker 1 (40:05):
We definitely need more data. And what's in the star
definitely does have an impact, Like if there's magnesium in
the atmosphere, then those lines are removed from the star.
But that doesn't really change the star that you see
from the naked eye because you can't tell that individual
slice of the spectrum has been removed. It still looks
red to your eye. But if you pass these things
through a prism, you will notice that different stars, even
(40:27):
if they have the same temperature, have different spectrum because
they have different lines removed, and that tells you what
they're made out of. Most stars still totally hydrogen, like
the universe started out all hydrogen. Mostly still hydrogen, but
the elemental mixture does affect the lines in the atmosphere,
so it will affect the color of the star technically.
Speaker 2 (40:46):
So we've talked about a lot of different things that
influence star color. When I look at at the stars
at night, Am I understanding correctly that the thing that
mostly determines the color I see is how hot they're burning?
Speaker 1 (40:57):
Yeah, which is mostly determined by how big they are?
Speaker 2 (41:00):
Okay?
Speaker 1 (41:01):
So yeah, Redder stars are smaller and bluer stars are bigger.
Speaker 2 (41:05):
Got it. I'll appreciate that so much more now.
Speaker 1 (41:08):
And it's incredible what we can learn about these stars
just from the pattern of the light, or that we
even figured out that you can break up light into components,
and that it contains all of this useful information right
always makes me wonder what happened we yet figured out
what information is landing on the planet screaming itself, screaming
clues about the universe that we haven't yet figured out
(41:28):
that in a few hundred years people will be like,
oh my gosh, you guys were such idiots.
Speaker 2 (41:33):
You know, I wonder the same thing in biology, What
are the things that we're missing that people will laugh
at us for in the future. But you know, all
you can do is take incremental steps forward and then
be willing to take those steps backwards when you learn
that you're wrong.
Speaker 1 (41:45):
Yeah, and take things apart and try to learn about
them right exactly. Pass your parasites through a prism, See
what bits they're made out of.
Speaker 2 (41:52):
Tell me what you find out, and everybody out.
Speaker 1 (41:55):
There come up with your favorite color and your favorite parasite.
Speaker 2 (41:58):
Ah, what's your favorite parasite? Daniel?
Speaker 1 (42:02):
All the ones that are not in me?
Speaker 2 (42:04):
Oh, that's a lot, that's a lot. You must really
like parasites.
Speaker 1 (42:08):
I approve of their choice to not be inside me
right now.
Speaker 2 (42:10):
Yes, well, you know, as we were telling a listener
the other day, they don't have a lot of choice.
But I'm glad that they're not in you.
Speaker 1 (42:17):
And I hope that this has helped you appreciate the
beauty of the night sky. And next time you're out
camping or on a beach in Costa Rica protecting turtles
from raccoons, you'll appreciate that the night sky is colorful
and that those colors communicate information about the nature of
the universe, what's going on in the hearts of these big,
furious balls of fusion.
Speaker 2 (42:37):
Enjoy the night sky. Friends. Daniel and Kelly's Extraordinary Universe
is produced by iHeartRadio. We would love to hear from
you we really would.
Speaker 1 (42:52):
We want to know what questions you have about this
extraordinary universe.
Speaker 2 (42:57):
We want to know your thoughts on recent shows, suggests
for future shows. If you contact us, we will get
back to you.
Speaker 1 (43:03):
We really mean it. We answer every message. Email us
at Questions at Danielankelly.
Speaker 2 (43:09):
Dot org, or you can find us on social media.
We have accounts on x, Instagram, Blue Sky and on
all of those platforms. You can find us at D
and K.
Speaker 1 (43:19):
Universe will be shy right to us
The best view in the universe is not from the
top of the Seer's Tower or the birds Dubai. It's
not from some seaside hotel. It's not from the top
of Mount Everest. It's from your backyard. On a dark night.
You can look up at the universe and see across
billions and billions of miles. Every view on Earth pales
(00:27):
in comparison to the vista you see across this ocean
of space. Though they are impossibly distant, you can still
see balls of gas furiously fusing, burning brilliantly enough that
they can be seen with your naked eyeball. And if
you look closely, you'll notice something incredible. There's a rainbow
of stars out there. White, blue, yellow, red. It's a
(00:49):
fabulously colorful universe. What does that mean? Why are stars
different colors? We'll be digging into the physics and countering
some usual pop sigh misinformation along the way. Welcome to
Daniel and Kelly's extraordinarily fabulous colorful Universe.
Speaker 2 (01:19):
Hello, my name is Kelly Windersmith. I study parasites and
space and I love looking at the night sky.
Speaker 1 (01:26):
Hi. I'm Daniel. I'm a particle physicist, and I don't
have a favorite color.
Speaker 2 (01:31):
I do. Mine's purple. Why don't you have a favorite color?
Speaker 1 (01:35):
I don't get the whole principle of choosing a favorite.
Like I like the colors, they're all nice. Why do
I have to pick one and say this one's my
favorite color? Like, I like purple, it's nice. I like orange. Yellow,
it's pretty good too. Blue is so soothing. I like
the colors. Grown do you have a favorite child?
Speaker 2 (01:52):
You know? You and Zach. I'll ask Zach what's your favorite?
Blah blah blah, and he's like, I don't see any
reason to pick a favorite. And I'm like, because people
use this as a conversation starter, and you're a conversation killer.
Speaker 1 (02:05):
I was just gonna say, it's the way people start conversations.
But it feels to me like dishonest, it's false. It's
like it's not what you really think or feel. It's
just like, oh, you like red, I like green. You
know it's not sincere, so it doesn't start a good conversation.
Speaker 2 (02:19):
I think it's implied that, like, you're not married to
that color for the rest of your life. I was
doing a book signing. I was like, oh, so tell
me something about you. And he's like, I hate small talk.
Speaker 1 (02:28):
And I was like, oh, okay, and that's the end
of this conversation.
Speaker 2 (02:33):
I did stop talking. I was like, okay, all right,
I don't know what else to say. Now you've ruined
the question I was planning on asking you today because
it involves the word favorite. But I was going to
ask you about your favorite or the best star viewing
experience you've had, Like when was the moment when the
sky was most clear and you could see the farthest.
Speaker 1 (02:50):
I think one of my favorite observing moments is not
actually looking at stars, because you know, stars are hard
to make out any features for because they're so far away.
They're sicly just points of light. But stuff in our
Solar system that you can actually see. And back in
the mid nineties, I was working on a project over
the summer right when comet shoemaker Levee was about to
(03:11):
slam into Jupiter, and I had access to a super
high speed camera and so we pointed it at Jupiter
hoping to catch really high speed photographs of the impact
to see like, you know, planet sized plumes of fire
emerging from it. It was super cool.
Speaker 2 (03:27):
I mean, I do feel like I asked you something
like what's your favorite color? And you answered macaroni and cheese.
But that is a very cool story. Did you see
what you wanted to see?
Speaker 1 (03:36):
Yeah, we got to see shoemaker levee impact on Jupiter.
Unfortunately impacted around the back of Jupiter, so we didn't
see the collision itself, but we did see the plume
coming up over the limb of Jupiter. Really pretty amazing.
I sort of remember it in black and white. I
can't really answer your color questions, but Jupiter does have
a lot of beautiful colors. See, it doesn't just pick.
Speaker 2 (03:55):
One that's amazing. And you keep sort of wiggling around
my questions. That's fine, that's fine. What you're saying is interesting,
so it's fine for content.
Speaker 1 (04:04):
And i'd ask you what your favorite color is, But
you're wearing a color right now. You literally have paint
all over your arms. That's your favorite color.
Speaker 2 (04:11):
Well, that's my favorite color for my laundry room renovation
that I'm working on right now. But my favorite star
viewing moment I got really lucky one. So I was
in Costa Rica and I was in a community where
there was a big leather back sea turtle conservation project
going on, and leather back sea turtles can get distracted
by lights and then they move towards those lights and
then they don't go out to the ocean after they
(04:33):
hatch like they're supposed to. So the whole community had
very dim red lights and they turned off all of
their bright lights at night, and so we were sort
of in the middle of nowhere and all the lights
were off. So my job at two am was to
guard the hatchery so that raccoons wouldn't dig up the
leather back sea turtle eggs and eat them.
Speaker 1 (04:50):
Wow.
Speaker 2 (04:50):
So it was like two am in Costa Rica. It
was the middle of nowhere. All the lights were out,
and it was just the most amazing view of the
Milky Way and you know, shootings stars and at any
time there could be baby turtles. Like that's Pete Kelly
life right there. I'd much rather spend time with my kids,
But that was amazing.
Speaker 1 (05:08):
That sounds like a magical moment. Did the night sky
look anything like your outfit does right now?
Speaker 2 (05:13):
Yeah, except a fewer holes in it. This is also
what I wear. What I'm doing some renovation work. I
don't know, it's comfy.
Speaker 1 (05:19):
For the audio only listeners. Kelly's wearing something which looks
like it has star patterns on it.
Speaker 2 (05:24):
It does. And my daughter has a matching outfit that
we wear sometimes, and she still wants to wear even
though this dress has holes in it. Whenever she wants
to wear a matching outfit, I am all in because
I imagine it's like weeks or months before she's too
old to want to do that. So every day it's
an automatic.
Speaker 1 (05:39):
Yes, You've got to savor those moments when the kids
still want to spend time with you, because pretty soon
they're going to grow up and move on.
Speaker 2 (05:46):
I know, I know your kid's going to college.
Speaker 1 (05:50):
And kids are not the only thing growing up and
changing and moving on. Everything in the universe is going
through its own life cycle, including the stars in the sky,
burning and glowing and changing colors as they do.
Speaker 2 (06:02):
Yeah. So when I was listening to your introduction, I
was realizing that I don't appreciate all the colors of
the stars in the sky. I just think of them
as white and sort of look at them as sort
of a blurry something. I don't pay attention to the
individual colors, the palette of the universe. So I'm excited
that next time I look at the night sky, I'll
(06:22):
pay a little bit more attention, and I'm excited to
learn more from you today.
Speaker 1 (06:25):
Yeah, the universe is very colorful, but it's not just
to please you or to start conversation among two am
sky watchers who can otherwise talk to each other. It's
for physics reasons, and the colors in the night sky
are going to tell us a lot about what's going
on inside those.
Speaker 2 (06:41):
Stars, as long as it's not for chemistry reasons.
Speaker 1 (06:46):
So this is actually part one of a two part
series about why stars have colors and what it tells
us about the universe, which ends up with a really
interesting story about yet another overlooked female astronomer.
Speaker 2 (06:58):
Oh I love when I'm surprise. While we're recording, I
didn't realize this was a two parter.
Speaker 1 (07:04):
I just realized as the two parter because I'm preparing
that other episode, and now I'm understanding, Oh my gosh,
this is the perfect setup for that episode. So good
job Daniel realizing that in real time.
Speaker 2 (07:14):
Welcome to Star Week.
Speaker 1 (07:17):
This is how carefully we plan the episodes on the podcast.
All right, So before we dig deeper, I was curious
if people knew why stars had different colors, and so,
as usual, I went out to our group of wonderful, clever, hilarious,
well informed, good looking volunteers to ask them if you
would like to join their ranks for future episodes. Please
(07:38):
don't be shy, right to us two questions at Danielankelly
dot org. We'll hook you up in the meantime, think
about it for yourself. Do you know why stars are
different colors? Here's what our volunteers had to say. We
know the color here on Earth is based on different
wavelengths of light, so I'm assuming that the same principles
(08:00):
apply to stars.
Speaker 3 (08:02):
Red shift the including distance from and speed away from
the observer.
Speaker 4 (08:06):
Color of the stars related to its size. So the
older the stars, the more it's been able to fuse,
the heavier elements you get different.
Speaker 1 (08:13):
Spectrum their temperature and the element.
Speaker 5 (08:18):
I know that big hot stars are described as below
and small coola stars described as red, and middlely ones
like our sun are yellow.
Speaker 4 (08:29):
Well, I think the color of stars depends pretty well
solely on their age.
Speaker 3 (08:35):
I think stars are different colors based on the levels
of hydrogen and helium in the star.
Speaker 4 (08:39):
Red ones are shy, and as they get closer they
turn red.
Speaker 1 (08:42):
Blue ones are kind of cool, so they're going away
from you. They don't care.
Speaker 2 (08:47):
Different elements of different colors, and stars throughout their life
fuses loads of different elements.
Speaker 1 (08:54):
I think stars are different colors because of the gases
that are in them, and also because of the temperature
of the star.
Speaker 4 (09:01):
Probably due to their composition, different elements they are made
up of, and perhaps also their size and perhaps just
how they're burning their energy output.
Speaker 1 (09:11):
Also, the universe believes in diversity, equity inclusion, and that's
why they're different colors.
Speaker 2 (09:16):
The temperatures are different and that causes the black body
radiation peaks to be at different wavelength.
Speaker 4 (09:21):
Stars are different colors because they have different elements and
they burn at different temperatures, which changes the color we see.
I'm really not sure where the stars are different colors,
but if I had to guess, I would say it
had to do something with where they were at in
their life cycle and the gases that they are made
up of.
Speaker 3 (09:41):
I think stars are different colors because the way they
expand and like the gases inside of them like as
they expand and get hotter, I think they like change
colors and stay those colors their lifetime.
Speaker 1 (09:55):
I would think that stars are different colors because they
emit different light particles, but I think a nonscience the
answer would be that they have a cool aura.
Speaker 2 (10:05):
Amazing answers I chuckled, and some really clever insights here.
What did you think, Daniel?
Speaker 1 (10:10):
I think there's a lot of interesting stuff going on here.
The picture I'm putting together of what people imagine causes
the different colors of stars is that this different fusion
happening with like different ingredients. Maybe you have more metal
here and more metal there, and that's somehow changing what's
going on, and that's changing the burning of the star
the way you can put copper in a Bunsen burner
(10:31):
and it turns green, for example.
Speaker 2 (10:33):
That is my understanding coming into this conversation is that
I do think it depends on what elements are getting
burned and how hot. But often I'm wrong.
Speaker 1 (10:43):
So I suspect a lot of you listening out there
probably think the same thing, which is why we do
this segment to orient us and understand where we need
to take you from your current understanding to a deeper,
more physical understanding. So we hope that by the end
of the episode you have a deeper view of why
stars have different colors, because the answer is a little
bit more subtle than anything we heard from our volunteers.
Speaker 2 (11:03):
All Right, I love it. Let's dig in and let's
start with the basics. Tell me about light and color.
Speaker 1 (11:08):
Right, So some of the listeners commented that different colors
mean different wavelengths, and that's true. Of course we're interested
in like why is flight emitted at different wavelengths? But
fundamentally it's important to understand the physical mechanism here, like
why are we seeing different colors? And they're right, because
light is electromagnetic radiation. The universe is filled with electromagnetic field,
and that field can ripple, and when electrons in alpha
(11:30):
centauri wiggle, they cause ripples in that field because electrons
are connected to that field. Right, When electron moves, it
wiggles that field, and that wiggle is what we see
as photons, for example. And those wiggles have frequencies, and
the frequencies correspond to different wavelengths, and those wavelengths correspond
to colors.
Speaker 2 (11:50):
I feel like a bunch of pieces actually just click
together in my head that should have clicked together much earlier,
but there they are, okay.
Speaker 1 (11:57):
Click And the same mechanism is like how radio works
wizer an antenna because electrons are going up and down
in the antenna, and as they do so, they make
the photon field wiggle just the same way, like if
you're holding the end of a jump rope and you
go up and down, you make wiggles down the jump rope.
It's exactly the same mechanism.
Speaker 2 (12:14):
I think the piece is just unclicked. Oh no, I
think I don't understand the electrons going up and down
the antenna. Thing is it just radio waves are traveling
through the antenna and that's radio frequencies.
Speaker 1 (12:26):
Well, an electron has an electric field around it, right,
If the electron just sits there, the electric field doesn't change.
What happens if the electron moves up, well, the electric
field also has to move up. Or if the electron
field moves up and then down, the electric field moves
up and then down. But it doesn't do so instantly,
Like if you wiggle an electron in an antenna that's
a mile away from me, I don't instantly see it
(12:47):
change in the electric field. It has to propagate and
So if the electron is going constantly up and down
and up and down, then it's making waves up and
down in the electric field that propagate out away from it.
And if I'm a mile away and i have electrons
in my antenna, those wiggles in the electric field are
going to push on my antenna's electrons, which are going
to go up and down, and then I'm going to
read that out as current. So yeah, the electrons in
(13:10):
descending antenna wiggle the electric field, which wiggles. Electrons in
the receiving antenna, which move and can be picked up
by my electronics can be reclick yep, yah yah. And
so the different colors are different wavelengths of those wiggles.
Photons are wiggles in the electromagnetic field, but they can
have different wavelengths. Right. They can be really really narrow,
(13:32):
so they're like very high frequency, like ultraviolet or purple.
They can be really really long, so they're like radio
waves or red light or infrared light. And there's a
potential source of confusion here. Remember these things are quantum mechanicals,
So photons are discrete units. Like you can have one
photon or two photons, but you can't have two point
seven eighty one photons, but you can have photons of
(13:54):
any energy. That's a continuous spectrum, So there's an infinite
number of frequencies on the spectrum.
Speaker 2 (14:01):
So does that mean there's an infinite number of colors?
Speaker 1 (14:04):
Mmmm, yes, great question. Right, So there are an infinite
number of frequency choices for a photon. But colors are
things that we experience in our mind. Right. There are
responds to signals on the optic nerve. So let's talk
momentarily about the physics of the biology of what's going
on there. You have photons that enter your eyeball and
they hit the back of the eyeball and the back
(14:25):
of the eyeball, there are three different kinds of cells
that respond to different colors. They have proteins on them
that operate like little switches, and when they absorb a
photon of the right color, they flip that switch and
they send a signal up the optic nerve. This whole
continuous spectrum of photons gets converted into three numbers, how
much did you turn on cone one, Cone two, and
(14:45):
cone three? And then your brain interprets those and generates
the experience of the color. So the color is actually
in your mind. It's not on the photon, right, we
say red photon or green photon when we're being sloppy,
but really the boon has an energy and the experience
of color is only in your brain.
Speaker 2 (15:03):
And we got a great question on our discord channel,
which you can join by going over to Danielankelly dot
org and clicking the invite and Quicksilver the DIRG Sorr
who was the discord quicksilver the DIRG anyway, this individual
going by the moniker Quicksilver, the DIRG wanted to know
something about why we see the colors that we do see.
(15:26):
And actually, our distant ancestors had two kinds of light
cones and we have three, and so why do we
see the colors that we see. The answer, really, at
the end of the day is we're not one hundred
percent sure, but we think what happens is that there
was a gene duplication event, and these happens every once
in a while in our genome. And so now instead
of having two different kinds of cones, you had two
(15:48):
different kinds of cones, but three different genes for those cones,
and over time selection tinkered with that extra new gene
and we ended up with the ability to see the
color red. Already see things like green, and the thought
was that seeing colors like red allowed our primate ancestors
to differentiate between different kinds of fruits and in particular
(16:09):
whether or not the fruits were ripe. And there are
some macaques that only have two types of cones and
some macaques that have three types of cones in the
same species, there's this variability. Some studies have found that
if you have three types of cones, you get ripe
fruits quicker and eat them quicker, which shows a benefit.
But other studies and other kinds of macaques haven't found
that because it's biology, so it depends depends there you go.
Speaker 1 (16:32):
And I think you put your finger on it, because
the important thing here is the ability to distinguish different colors, right,
But I think that depends not just on like the
number of different kinds of cones you have, but also
the processing power behind it. I know that like mantis,
shrimp are famous for having like more than ten different
kinds of cones, but they actually apparently are terrible at
distinguishing different colors because they have almost no neural processing
(16:55):
behind it. I think they might just like experience ten
different literal colors. We have a huge number of different
colors that we can distinguish because we can do this interpolation, right,
That's what your brain is doing is it's getting like, oh,
a little bit from the bluish cone, a little bit
from the reddish cone, a little bit from the greenish cone,
and it's saying, okay, what color would give me this
(17:15):
pattern and then sort of inferring what color might be there.
But again, the experience of color, the reason like red
is reddish and blue is bluish has nothing to do
with the photon. That's something your brain has assigned to
it has invented, has fabricated. Right in principle, it could
make up a new color. If you've got a new
cone and planted that was sensitive to the ultraviolet, that
your brain could invent a new experience, not one that's
(17:38):
a combination of the other ones, but like a real
novel experience to represent the signal from the UV cone.
Speaker 2 (17:44):
And there are insects that can see in the UV.
And it makes me so sad when I look at
a beautiful flower and think there's layers that I'm missing.
But anyway, I'm guessing based on our examples that you
and I both read An Immense World by Ed Young,
because we both seem to have cherry picked examples from
that fantastic book.
Speaker 1 (18:01):
It is definitely a great book, a lot of fun,
and recommend everybody read that, especially if you're interested in
physics and biology, because it covers both of those topics
about our experience.
Speaker 2 (18:09):
Okay, so the three kind of cones that we have
determine what colors we can see in the night sky.
Are we missing a lot or are there ultraviolet stars
out there that we're missing.
Speaker 1 (18:20):
We're definitely missing a lot because we can only see
a certain range of photons ultraviolet and infrared. Everything below
that and everything above that we can't see, and the
sky definitely is bright in those colors. That's why, for example,
we have radio telescopes and infrared telescopes and ultraviolet telescopes
because stars and other different phenomena emit differently in those
spectrum and if you can see those, you can see
(18:41):
different kinds of things. Also, the universe is transparent differently
in different frequencies. Some frequencies of life can go through
dust clouds and others can't, and so if you want
to see through dust clouds, you've got to change your frequency.
So absolutely the night sky looks very different outside the
visible range our star, and of course peaks right in
the center of the visible range, which again is no coincidence. Right.
(19:05):
If you're going to evolve vision, you might as well
evolve it to be able to see the most common
photons that are around you. So if we had evolved
around a redder star, for example, probably our visible range
would be lower. The Sun is an unusual star. Most
of the stars out there are redder than our star.
Our star is yellower than most stars out there, so
we may have a different visual range than most of
(19:26):
the aliens.
Speaker 2 (19:27):
So are you postulating that the color of the star
determines the colors that we see, because I feel like
that's not an evolutionary argument that I understand. Does the
color of our star impact the color of things on
Earth that are important for food, mating or running away
from a predator?
Speaker 1 (19:43):
I think it makes sense for us to be most
sensitive to the photons that are most present here on
Earth for that range. Whether we can experience two or
seven or three or whatever, I think is a different question.
But for us to be sensitive to the most common
kind of photons makes sense to me. I'll give you
that you're skeptical. Why A you're skeptical?
Speaker 2 (20:02):
So I totally follow the argument that the most common
kinds of photons in the environment would be the ones
that were good to sense. But if for some reason
those didn't translate into an increased ability to find your
food or an increased ability to recognize a mate, then
I don't necessarily think that selection would hone in on those.
And there's so much variability and what animals can see.
(20:24):
You know, there's plenty of dichromates, so they don't have
three kinds of cones and they get along just fine.
So yeah, how do you explain the variability?
Speaker 1 (20:32):
Then that's a great point. And I can give you
an example to support your point, which is neutrinos. Neutrinos
are everywhere in our environment, but pretty much useless because
everything is transparent to them, and so it wouldn't be
great to develop a neutrino eyeball even though they're everywhere.
So you're right, just being ubiquitous isn't enough to have
to be useful. And so I think the combination of
(20:53):
the fact that they are everywhere, and stuff on Earth
tends to not be transparent to them, makes them useful
for us to see things. So I think you're right.
It's more complicated than just the physics of this region
has to also be like useful in your environment. For sure.
I have no idea why you would have two or
seven cones.
Speaker 2 (21:11):
I guess both of our fields are useful. You ponder
the question Daniel and I were just debating during the break,
And when we get back, we'll talk about why stars
have different colors? All right, and we're back. You look
(21:39):
up at the night sky and there are lots of
different colors of stars. Though I'll be honest, I missed
that in the past. I'm gonna be paying much more
attention now. So Daniel, why do those stars have different colors?
Speaker 1 (21:50):
So there's sort of three big factors that control what
color a star is in our sky. One is what
it's made out of, another one is its temperature, and
the last one is its velocity. So let's do those
in order. What it's made out of. This is the
one that's connected to your experience of like putting copper
in a Bunsen burner and seeing it glow green. That's
(22:10):
because atoms are quantum mechanical little objects and they have
energy levels. You know, electrons around an atom can't just
be at any energy willy nilly. There's a ladder of
energies there, and because there's a ladder of energies there,
they can only eat and emit photons of certain energies,
the ones that let them go up or down the ladder.
So when an electron is around an atom and a
(22:30):
photon comes by, if that photon has just the right
energy to take it up one or two or seven
rungs on that ladder, it can eat that photon. You
might think I don't care about what photons the electron eats,
but actually does matter what it absorbs and what it reflects,
because what it reflects is what you see. Right, If
you're looking at something that's blue, it's not blue because
(22:50):
it's eating blue photons. It's blue because it's eating everything
but the blue photons. It's reflecting blue photons back at you.
Remember you see something blue because some light in the
blue range has hit your eyeball and you responded to that.
So it's important what energy levels an atom can absorb.
And the same is true also in the reverse, Adam's
(23:11):
in midlight. That's what's happening to the copper in your
Bunsen burner. It's getting hot, and the inverse process is happening.
An electron jumps down energy levels and gives off a photon,
a green photon in the case of copper.
Speaker 2 (23:22):
That always felt very counterintuitive to me, that the color
that I'm seeing is the color that's being given off
by something. It almost feels like everything is disguising itself
in some way. I don't I don't know why my
brain ahead trouble wrapping itself around that.
Speaker 1 (23:36):
I totally remember the first time I understood that. I
was like nine, and I was like, oh my gosh,
things that are blue are not actually blue, they just
look blue. And then I realized, well, maybe that's what
it means to be blue, to look blue. But yeah,
I had the sense that like, if I could see
through these photons to what things actually looked like, I
could perceive a deeper truth to the universe. But the
(23:56):
universe is kind of a construct we've assembled in our
head from our experience of it, and there's a lot
of that that's imagined, that's put together from our experience
and the way we paint these colors on things is
just one layer of that.
Speaker 2 (24:08):
Yeah, man, Yeah, I totally agree though.
Speaker 1 (24:15):
Yeah, but that's the joy physics. It helps you separate
what's really out there and what you know about it,
which you don't know about it, which parts you're building
in your mind. Super fascinating, even if it is philosophical
and could never be understood. So the next piece to
understand is why things have different colors? Right, We said
that atoms have energy levels, and electrons can jump up
energy levels eating photons or down energy levels emitting photons,
(24:38):
and those photons have specific energies corresponding to those gaps. Well,
different atoms have different energy levels. Copper and mercury and
helium and hydrogen all have different energy levels. Because the
solutions to the Shorteninger equation are different, you got different
numbers of protons, and the whole configuration of the atom
is different. Every atom has its own unique ladder, which
means that they have like a fingerp If you take
(25:01):
an element and you take a gas of it and
heat it up, and then you take the light from
that pass it through a prism to spread it out,
you'll see that Each element has its own unique fingerprint,
its own spectrum. They'll have these little bands like a
blue one and a red one, or a different element
will have like a green band and the blue band
will be shifted over. So you can tell what something
(25:21):
is made out of just by looking at a spectrum
of a hot gas. So there's two things that are
happening here. You have hot gas, it glows in certain colors, right,
And if you have more oxygen, you glow in these colors.
You have more neon, you glow in those colors. And
our whole next episode is going to be about using
spectroscopy to understand what stars are made out of. But
this also absorption, Right, if a star has an atmosphere
(25:42):
and that atmosphere is mostly neon, for example, then it's
going to absorb that light. So if you have a
hot blob of gas, it emits light to those frequencies.
If you have light that passes through an atmosphere, then
it absorbs those frequencies.
Speaker 2 (25:57):
So it feels to me now like we have an
infinite number of combinations of elements that could be emitting
and like gases that could be absorbing. How do we
make sense of the output given that there's now so
many different options, and it's probably not just one element
that's emitting at a time. There's probably a couple different
things that are emitting. And I'm overwhelmed.
Speaker 1 (26:16):
Yes, it is overwhelming. It's a hard problem, and it
was solved by a very clever young lady around the
turn of the century. And we're going to talk about
that in the next episode. Okay, but even if you
mix all these elements together, what you get are a
bunch of different spikes Like these are narrow emission lines.
You can't put them together to get a broad spectrum.
And that's not what most of the light from the
stars is. This is like people's conception, but most of
(26:37):
the light from the star comes from a completely different process.
It's not from atomic emission and absorption. It comes from
the plasma inside the star just glowing at a certain temperature.
Speaker 2 (26:48):
What all right, we were all wrong, audience and friends
of mine. Okay, so Daniel, let's move on to the
next thing. Then tell us more about this thing that
actually contributes most of the color.
Speaker 1 (26:57):
Yeah, so we said that the color of stars comes
from what they're made out of, and that has to
do with atomic absorption, and emission mostly in the atmosphere
of stars, but also from its temperature. And so that's
what we're going to dig into next. And there's a
process here that has a terrible, absolutely, terrible, very misleading name.
It's called black body radiation that describes why stars glow
at certain temperatures. And it's terribly the name because a
(27:19):
star doesn't seem like a black body. Right.
Speaker 2 (27:22):
Nope, you guys did it again.
Speaker 1 (27:23):
But in physics, we have a model of some hypothetical
object with no reflection, Like any photon you shoot at
it, it will absorb it and just like heat up. And
even in the hypothetical version, it's not black. It just
means that it doesn't reflect. It glows because of its temperature.
Everything in the universe that has a temperature and is
made of charged particles will glow. Like if you have
(27:43):
fluorescent lights in your ceiling, you look up that has
a hot gas in it that's glowing because of its temperature.
Or you're glowing right now, Kelly, because of your temperature.
Not in the visible light, but if I put on
night vision goggles or infrared goggles, I would be able
to see you emitting light.
Speaker 2 (28:00):
What is the physics definition of glow is it just
releasing photons or something.
Speaker 1 (28:04):
It's just releasing photons because you have charge particles in you,
and charge particles are always interacting and moving around and whizzing,
and when they do so, they emit photons. Like an
electron can't change directions without emitting a photon. That's how
it does it. And an electron is flying to the
universe and it wants to curve along a magnetic fields
or something, it's got to push out a photon in
(28:24):
the other direction to conserve momentum. Now you have a
big blob of gas with all sorts of charge particles
whizzing around, they're going to be constantly emitting photons, and
they emit a very broad spectrum. Not like the atoms
we talked about, we have very specific energy levels. This
black body radiation is a very broad spectrum, but it
has a peak that depends on the temperature. So really
cold things tend to emit in the infrared. Warmer things
(28:47):
emit invisible. So for example, you take a piece of metal,
it's glowing right now, even if it's cold, just in
the infrared. You can't see it. Put in the oven,
heated up, put it in the forge. It starts to
glow red, and then it glows white. Right. White? Hot
is very hot? Why because now it's hot enough to
be glowing in the visible Keep heating it up. It'll
start to glow in the ultra violet. You won't see
(29:09):
it anymore, but it be super duper hot. The temperature
of something determines the peak of its emission, right, So
everything in the universe that's made of charge particles glows
at a certain temperature, and that temperature controls the frequency
of the emission.
Speaker 2 (29:23):
Okay, all right, a few questions. So when an electron
kicks out a photon, is it still an electron?
Speaker 1 (29:28):
It's still an electron because a photon is neutral. Yeah.
Speaker 2 (29:30):
How many photons can an electron kick out? Can I
just do that all the time?
Speaker 1 (29:36):
Oh my gosh, what an amazing question. It makes me
think of an electron as like having a bag of
photons that they could run out of, right, like fuel
You think of like rockets, right, and they need some source. No,
an electron has an infinite number of photons. Remember, these
are just wiggles in the electromagnetic field, right, And so
it's not like it's kicking off some substance. But in
(29:57):
order to conserve momentum, you have to have some momentum
move to the ectromagnetic field and some momentum moves through
the electron field.
Speaker 2 (30:03):
Wow, okay, all right. So say you've got some iron,
and we talked about iron having emission line spectrums where
the electrons get excited and they jump to different levels
and they emit light and then you hate that iron
up and now it's glowing. Are you saying that the
glow is more important than the jumping of the levels.
Speaker 1 (30:28):
The most general answer is that it depends on what
it's made out of and its temperature, and in the
case of stars, it's mostly black body radiation. Like when
we look at the spectrum from the Sun, it's almost
all black body radiation. So that's definitely the most important effect.
And there's a combination of the two things. So you
have the star which is glowing very broad spectrum which
(30:48):
peaks right in the middle of our visual spectrum for
our star. But then the sun has an atmosphere, and
this atmosphere is gas and it's made out of various stuff,
and that atmosphere will eat that spectrum. So the light
we get from the Sun is a huge black body
peak with a few lines removed. That's absorption spectrum. So
if you look at the spectrum from the sun, you
(31:09):
see reds and yellows and greens and blues, but then
you see these black spots, these things that have been removed.
That tells you what's in the atmosphere of the Sun.
You can see the hydrogen lines have been removed, the
sodium lines, the helium lines, the magnesium lines, and so
that helps you figure out what's in the atmosphere of
the Sun. So the two things happening there is the
broad glow inside the sun, which we're not fully seeing
because parts of it have been removed as the Sun's
(31:32):
atmosphere eats some of those frequencies.
Speaker 2 (31:35):
That's amazing.
Speaker 1 (31:36):
Yeah, and so the last piece we talked about for
what determines the light that comes from a star is
the velocity. And a bunch of listeners pointed this out
that things that are moving away from you will be
red shifted, just like a police siren moving away from
you will have a lower sound than a police siren
moving towards you. It's just a Doppler effect. And so
as star emitting light as it moves away from you
is going to get red shifted, and we use this
(31:57):
red shift to measure that velocity. It's like a huge
the important thing in astronomy. A star moving towards you
would be blue shifted, and we can tell the red
shift in the blue shift because we know the typical fingerprints.
Like you get a star you've never seen before and
you want to measure its red shift. Well, you might think, well,
how it I know it's impossible. If the star has
hydrogen lines but they're shifted by a few nanometers, and
(32:19):
it has magnesium lines and those are shifted by the
same number of nanometers, then the most likely scenario is, oh,
this isn't made of some new super weird metal that
looks like magnesium and hydrogen but shifted. It's just magnesium
and hydrogen and it's been shifted due to the red shift.
So you can fit these lines, these specter, these absorption
and emission lines, to tell you the frequency shift of
(32:40):
an individual star. And so that definitely affects the color
of the star in the sky. And almost everything in
the sky is moving away from us, so they're all
red shifted.
Speaker 2 (32:50):
I'm having one of those moments where I'm just so
proud of our species for figuring all of this out,
Like that's so many different things to keep track of.
It's so incredible that we got there and that we
understand all of this stuff and anyway way to go humans.
Speaker 1 (33:03):
This is the amazing thing about astronomy is that you
cannot leave the Earth. Mostly you've got to figure out
the puzzle of the universe from these clues. And we
didn't assemble this experiment in this way. We stumbled over
these things. People had moments of insight where they realized,
hold on a second, this pattern actually reveals this thing
about the universe. Those are incredible realizations, so powerful. And
(33:25):
let me just qualify what I said a moment ago
about everything moving away from us. Galaxies are moving away
from us, and those are all red shifted. Most of
the stars in the Milky Way are held together by
the gravity of the Milky Way, and so those aren't
red shifted and moving away from us. The stars in
the night sky are the ones from the Milky Way.
Those are the ones we can see. They're not red shifted.
But other galaxies are red shifted.
Speaker 2 (33:46):
All right, Well, that is amazing. Let's take a break,
and when we get back, we're going to talk about
the color of our very own sun. All Right, we're back,
(34:10):
and Daniel wants to tell us about why Niel de
grass Tyson is wrong.
Speaker 1 (34:14):
I don't want to say that. I do want to
dismantle a lot of pop sign myths that you.
Speaker 2 (34:19):
Hear from Neil de grass Tyson.
Speaker 1 (34:22):
I didn't say that. I didn't say that. I just
want to say that, you know, on this podcast, we'd
like to dig deep, well past the usual pop side
explanations and tell you what's really going on. So you know,
we're interested in the colors of the stars in general.
But of course our sun is near and dear to
our hearts. Why does the sun have its particular color?
And the Sun's color is actually fascinating because if you
(34:42):
were out in space and you were looking at the sun,
it's white, right, And what does it mean for the
sun to be white? White isn't like a color. It's
a mixture of the colors, and it's sort of the
way your brain responds when you see a very broad
spectrum of light across the visible range. So out of space,
the sun is white. Here on Earth because of the
effects of the atmosphere. The sun looks a little yellower, right,
(35:05):
because the atmosphere tends to scatter blue light, which is
why the sky, which doesn't have its color of its own,
looks blue, right, because it's reflecting blue light. Air itself
is not blue, but we see it as blue because
it's reflecting blue light. And so the sun has some
of the blue removed, which makes it look a little
yellower to our eyes.
Speaker 2 (35:23):
Oh that's so cool. And again yet another thing that
we had to account for to understand all of this stuff.
Speaker 1 (35:28):
Amazing, And the reason the sun glows at this color
is because of its temperature. The surface of the Sun
is about five thousand kelvin and what we're seeing when
we look at the Sun is its surface, right. We
can't see through it. It's opaque. Another bit of popsight
you hear a lot is that it takes like thousands
of years for a photon to go from the center
of the Sun to the surface. And like, I don't
(35:49):
even know what that means, because you know what's happening
is photons are made at the center of the sun,
but the sun is opaque, so then they just get
reabsorbed and they contribute to the overall heat of the sun.
An individual photon doesn't go from the center of the
sun to the edge of the sun. It just heats
up the sun and the surface emits a new fresh photon.
Speaker 2 (36:06):
Oh interesting, I mean I can't say that. You know,
Ada came home from the playground. It was like, did
you know that a photon at the center of the
sun takes you know, blah blah blah get to the edge.
I had never heard that before, but now I'm enlightened.
Speaker 1 (36:18):
I hear that a lot. Okay, And so you can
mimic the same spectrum that the sun makes by heating
up like a piece of tungsten to the same temperature.
You have a five thousand degree filament of tungsten, it
will emit in the same spectrum as the sun. Right,
it's not one hundred percent true, because the Sun is
not a perfect black body radiator, right, It does reflect
some things, it's not a perfect absorber. So the peak
(36:39):
of the distribution for the Sun is actually in the
green spectrum. And so this is why you might hear
some popseye folks being like, did you know the sun
is actually green?
Speaker 2 (36:48):
Okay? Well, so now let's take down that hypothetical. Did
you know the sun is actually green? Person?
Speaker 1 (36:54):
So saying that that the sun peaks in the green
is actually saying, if you had a perfect black body
radiator at five thousand kelvin, it would peak in the green.
But we don't have a perfect black body radiator. Our
son actually peaks in the violet. And where it peaks
depends a little bit on how you're doing the accounting,
like are you doing it in wavelength? Are you doing
in frequency? These things have a non linear relationship, and
(37:16):
so there's some like calculus that goes on there, but
which gets accounted into which bin And so it's not
really even true saying that the sun peaks in the green,
and even if it peaks in the green, you would
still see it as white in space. It's not like
out in space the sun is green or violet or
any of these things. Really, it's just most accurately said
that there's a broad spectrum that if the sun were
(37:37):
a perfect black body radiator, would peak in the green,
but it isn't, so it peaks in.
Speaker 2 (37:41):
The violet, which is my favorite color. So thank you, universe.
There we go.
Speaker 1 (37:45):
Why don't I see it on your arm. Then why
aren't you painting your launcher room violet.
Speaker 2 (37:49):
If we had been doing this podcast when I was
painting my bathroom, you would have seen my purple arm.
Speaker 1 (37:56):
Well, I have purple on the wall behind me as well.
See I'm a big fan.
Speaker 2 (38:00):
Oh it's a great color, best color, all right, So
tell me about how we get colors for some other stars.
Speaker 1 (38:04):
Yeah, So we've learned that star color depends on its
temperature and on what its atmosphere is made out of
and its velocity. So most of the stars in the
universe are smaller than our star. The Sun is a
big star compared to the average star, which is more
like a red dwarf. So smaller stars have less gravitational pressure,
so they're not as hot, so they burn and they
(38:27):
glow in the red more than in the yellow. So
that's why they're called red dwarfs. Right, So smaller stars
burn cooler and slower, they're longer lived, and they tend
to be redder. So a lot of the stars out
there in the universe are cooler on their surface than
are a star, but there are some that are hotter.
Blue giants, for example, super enormous stars very hot on
(38:47):
their surface because of the crazy fusion happening at their core,
they tend to glow in the blue. So if you
look at the spectra of stars, you see a really
big range. They are fewer that are bluer because those
are bigger and burn brighter and burn out faster. Red
stars tend to burn a lot longer, like our star
is going to last billions of years. Really big huge
(39:08):
blue stars can sometimes only last millions, where as little
tiny red giants we think maybe can last hundreds of
billions or even longer, much longer than the age of
the universe. So we don't really even have a measure
for it.
Speaker 2 (39:21):
Is there any relationship between the temperature which is star
burns and what we think its ability to sustain life is?
Speaker 1 (39:30):
Yeah, great question. We have this one clue, right that
we have life around a yellow star and not a
red star. And does that mean that life only happens
around yellow stars or are we weird and unusual and
most of the aliens out there look up at a
red sun. Yeah, we don't know. Red stars tend to
be a little bit more variable sometimes, and so there's
arguments there, but it's all based on this an equals
(39:50):
one so until we meet the aliens, we won't know
the answer to those questions.
Speaker 2 (39:55):
And I feel like if you could be at the
right spot next to a red star, that would give
you more time for life to pop up. But I
guess if it's more variable, not necessarily and it's colder,
and what does that do? And anyway, all right, yeah,
we need more data.
Speaker 1 (40:05):
We definitely need more data. And what's in the star
definitely does have an impact, Like if there's magnesium in
the atmosphere, then those lines are removed from the star.
But that doesn't really change the star that you see
from the naked eye because you can't tell that individual
slice of the spectrum has been removed. It still looks
red to your eye. But if you pass these things
through a prism, you will notice that different stars, even
(40:27):
if they have the same temperature, have different spectrum because
they have different lines removed, and that tells you what
they're made out of. Most stars still totally hydrogen, like
the universe started out all hydrogen. Mostly still hydrogen, but
the elemental mixture does affect the lines in the atmosphere,
so it will affect the color of the star technically.
Speaker 2 (40:46):
So we've talked about a lot of different things that
influence star color. When I look at at the stars
at night, Am I understanding correctly that the thing that
mostly determines the color I see is how hot they're burning?
Speaker 1 (40:57):
Yeah, which is mostly determined by how big they are?
Speaker 2 (41:00):
Okay?
Speaker 1 (41:01):
So yeah, Redder stars are smaller and bluer stars are bigger.
Speaker 2 (41:05):
Got it. I'll appreciate that so much more now.
Speaker 1 (41:08):
And it's incredible what we can learn about these stars
just from the pattern of the light, or that we
even figured out that you can break up light into components,
and that it contains all of this useful information right
always makes me wonder what happened we yet figured out
what information is landing on the planet screaming itself, screaming
clues about the universe that we haven't yet figured out
(41:28):
that in a few hundred years people will be like,
oh my gosh, you guys were such idiots.
Speaker 2 (41:33):
You know, I wonder the same thing in biology, What
are the things that we're missing that people will laugh
at us for in the future. But you know, all
you can do is take incremental steps forward and then
be willing to take those steps backwards when you learn
that you're wrong.
Speaker 1 (41:45):
Yeah, and take things apart and try to learn about
them right exactly. Pass your parasites through a prism, See
what bits they're made out of.
Speaker 2 (41:52):
Tell me what you find out, and everybody out.
Speaker 1 (41:55):
There come up with your favorite color and your favorite parasite.
Speaker 2 (41:58):
Ah, what's your favorite parasite? Daniel?
Speaker 1 (42:02):
All the ones that are not in me?
Speaker 2 (42:04):
Oh, that's a lot, that's a lot. You must really
like parasites.
Speaker 1 (42:08):
I approve of their choice to not be inside me
right now.
Speaker 2 (42:10):
Yes, well, you know, as we were telling a listener
the other day, they don't have a lot of choice.
But I'm glad that they're not in you.
Speaker 1 (42:17):
And I hope that this has helped you appreciate the
beauty of the night sky. And next time you're out
camping or on a beach in Costa Rica protecting turtles
from raccoons, you'll appreciate that the night sky is colorful
and that those colors communicate information about the nature of
the universe, what's going on in the hearts of these big,
furious balls of fusion.
Speaker 2 (42:37):
Enjoy the night sky. Friends. Daniel and Kelly's Extraordinary Universe
is produced by iHeartRadio. We would love to hear from
you we really would.
Speaker 1 (42:52):
We want to know what questions you have about this
extraordinary universe.
Speaker 2 (42:57):
We want to know your thoughts on recent shows, suggests
for future shows. If you contact us, we will get
back to you.
Speaker 1 (43:03):
We really mean it. We answer every message. Email us
at Questions at Danielankelly.
Speaker 2 (43:09):
Dot org, or you can find us on social media.
We have accounts on x, Instagram, Blue Sky and on
all of those platforms. You can find us at D
and K.
Speaker 1 (43:19):
Universe will be shy right to us
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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