Hey Crazies.
In the last video, we were talking about cosmological redshift and, at the end, I said this:
Unfortunately, to know there’s even been a redshift,
we have to know what color the light is supposed to be.
But that’s a topic for a another video.
I was gonna wait, but a bunch of you asked about it.
So wait no longer!
This is that video!
But we can’t address this issue without a deeper dive into the light from stars.
I mean, not literally, that would be bad.
I just mean that light can tell us a lot!
We saw in a previous video that the color of a star is only dependent on one thing:
Its surface temperature.
If we combine that with the star’s brightness, we can tell what type of star is it and how
long it’s been around.
Unfortunately, getting anything else out of that light is going to take a lot more work.
Let’s focus on our Sun.
It’s a yellow-white dwarf, but it’s mostly white.
It only looks yellow to us on the ground because the atmosphere scatters away some of the colors.
Astronauts, outside the atmosphere, see a white Sun.
So, the Sun is white, but white isn’t really a wavelength of light.
It’s what you get when you combine all the colors together.
What kinds of colors?
These kinds of colors!!
The ones in the visible spectrum.
Side Note!
In the last video, I made the spectrum look like this, except this magenta shouldn’t
be there because it doesn’t really exist.
Thank you, Alberto Torres, for keeping us accurate.
End of side note!
If all these colors come from the same place, it’s not very useful to see them all separate,
so our brain smudges it all together and calls it white.
The point is: Some of the colors we see are combinations of other colors.
It’s our brain trying to figure it all out.
Didn’t you just say a star’s color only depends on temperature?
Yeah, that’s a smidge of a lie though.
It’s a bit more complicated.
While it is true that most light coming from a star is because of its temperature
a little tiny bit of it is controlled by a couple other things.
Because of its temperature, the Sun emits ALL wavelengths of light.
Including wavelengths that aren’t visible.
However!
It doesn’t emit them all with the same brightness.
As you can see, most of the light coming from the Sun is in the visible range.
and it peaks around yellowish-green.
So this spectrum is not what the Sun’s light looks like.
It’s more like this. and that’s just the light from the particles
bumping into each other.
The light due to the Sun’s temperature.
But if you take a look at the actual colors coming from the Sun, it looks like this.
What?!?
Why are there missing colors?
They got absorbed as they were leaving the Sun.
They’re called “Absorption Lines” or in the case of the Sun: Fraunhofer Lines
named after Joseph von Fraunhofer, the physicist who first saw them.
after looking through one of these.
Well, he didn’t really look through it. He shined the light through it.
Don’t ever look directly at the Sun!
Anyway, each one of those dark lines comes as part of a set and each set corresponds
to a specific type of atom.
These are for Hydrogen.
These are for Helium.
and there are a ton of others.
We know which atom goes with which set of lines because we can create those same lines
here in a lab.
Not through absorption though.
If we get atoms excited, they’ll emit the same colors they can absorb.
These are the emission lines for hydrogen.
You can see they line up perfectly with 4 of the absorption lines from the Sun.
We can also do this for Helium or any other atom we’re looking for in the Sun.
It’s like an atomic fingerprint
except perfectly unique, so it's nothing like a fingerprint
It’s like Atomic DNA!
Using it, we can figure out what the outside of the Sun is made of
and, through plasma and nuclear physics, infer what the whole Sun is made of.
We can do this for all different types of stars
and get a good idea of what to expect for each one.
If we look at a star expecting to see this, but, instead, see this then we know it is
redshifted.
We know the star is moving toward us or away from us and how fast it’s going
but it took a bunch of physics to get there.
So knowing how complicated this is, does it make it more interesting or does it make it
scarier?
“Both” is an acceptable answer.
I’d like to hear your thoughts in the comments.
Thanks for liking and sharing this video.
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Hit that notification bell if you’re really serious.
And until next time, remember, it’s ok to be a little crazy.
Oh oh! One more thing!
Those of you who asked about Doppler redshift vs Cosmological redshift.
I’ll come back to that very soon.