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