41.
What Color is the Sun?
I'm Fraser Cain, the publisher of Universe Today.
Ask anyone, "what color is the Sun"? and they'll tell you the obvious answer: it's yellow.
(That's what the yellow crayons are for.)
But is it really?
Please don't go check, it's not safe to look directly at the Sun with your unprotected
eyes.
From our perspective it does look a little yellow, especially after sunrise or shortly
before sunset,
But don't be fooled.
If you could travel into space and look at the Sun without going blind, you'd find that
it's actually white, and not yellow.
(Your mother warned you about doing that too often.)
Using a prism, you can see how sunlight can be broken up into the spectrum of its colors:
red, orange, yellow, green, blue, indigo and violet.
(All the way across the sky.
What does it mean?)
When you mix all those colors together, you get white.
(This experiment was less successful with Skittles and a blender.)
Here's the strange part.
If look at all the photons coming in, our star is actually sending the most photons
in the green portion of the spectrum,
Our Sun appears yellow to us because of the atmosphere.
Photons in the higher end of the spectrum - blue, indigo and violet - are more likely
to be scattered away, while the lower end of the spectrum - red, orange and yellow - are
less easily scattered.
When the Sun is close to the horizon, you're seeing it distorted by more of the Earth's
atmosphere, scattering away the bluer photons and making it appear red.
When there's smoke and pollution in the air, it enhances the effect and it will look even
redder.
If the Sun is high in the sky, where it has the least amount of atmospheric interference,
it will appear more blue.
We're so familiar with the Sun being yellowish-orange, that astronomers will artificially change
the color of their images to look more yellowy.
(Be sad for their children.
White crayons show up really poorly on white construction paper.)
But really, the Sun looks like a pure white ball - especially when you're out in space.
Interestingly, the color of the Sun is very important to astronomers.
They use a technique called spectroscopy to stretch out the spectrum of light coming from
a star.
Dark lines in this spectrum tell you exactly what it's made of.
You can see which stars have high amounts of metals, or which are mostly hydrogen and
helium, leftover from the Big Bang.
This color also tells you the temperature of the star.
Cooler stars are actually redder.
Betelgeuse is only 3500 Kelvin.
Hotter stars, like Rigel, can get above 10000 Kelvin, and they look blue.
Our own Sun has a temperature of almost 5800 Kelvin, and when viewed outside of our atmosphere,
appears white.
in colour.
Thanks for watching.