Is Our Sun Really Yellow?

Ask anyone, “what colour is the Sun”? And they’ll tell you the obvious answer: it’s yellow. 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 viewpoint it does look a little yellow, particularly after sunrise or just before sunset. But don’t be deceived. If you could go into space and look at the Sun without going sightless, you’d find that it’s in fact white, and not yellow.

Using a prism, you can see how sunlight can be divided up into the variety of its colours: red, orange, yellow, green, blue, indigo and violet. When you combine all those colours together, you get white.

True Colour of Sun

Here’s the interesting part.

If we see all the photons coming in, our star is in fact sending the most photons in the green region of the spectrum. Our Sun seems yellow to us due to the atmosphere.

Photons in the upper end of the spectrum – blue, indigo and violet – are more possibly scattered away, while the lower end of the spectrum – red, orange and yellow – are less easily dispersed. When the Sun is near to the horizon, you’re viewing it distorted by more of the Earth’s atmosphere, sprinkling away the bluer photons and making it look red. When there’s smoke and pollution in the air, it boosts the effect and it will look redder.

If the Sun is high in the sky, where it has the smallest amount of atmospheric intrusion, it will seems bluer. We’re so acquainted with the Sun being yellowish-orange, that astrophysicists will artificially change the colour of their pictures to appear more yellowy. But in fact, the Sun appears like a pure white ball – particularly when you’re out in space.

Excitingly, the colour of the Sun is very important to astrophysicists. They use a method called spectroscopy to spring out the spectrum of light coming from a star. Dark lines in this spectrum tell you precisely what it’s made of. You can see which stars have high quantities of metals, or which are generally hydrogen and helium, discarded from the Big Bang. 

This colour also expresses you the temperature of the star. Cooler stars are in fact redder. Betelgeuse is just 3500 Kelvin. Hotter stars, like Rigel, can reach 10000 Kelvin, and they appear blue. Our own Sun has a temperature of nearly 5800 Kelvin, and when observed outside of our atmosphere, seems white in color.



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