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Depending on your perspective, you could argue that the sun is green, white, or yellow. Each argument has fair merits.
Without looking (because you never should), what color is the sun? Most likely you said yellow. If you’ve ever seen a video of the ISS, you may have said white. But Elon Musk is here to tell us that the sun is green. But what color is the sun, really? Is yellow. And white. And green. Not really!
The whole thing started when someone on Twitter explained Rayleigh scattering, the optical phenomenon that (partly) explains why the sky appears blue during the day. That’s when Elon Musk chimed in to point out that asking “what color is the sun?” is a funny question.
A good trick question is what color is the sun?
It appears white in space, but, as measured by the peak photon count, it is green.
— Elon Musk (@elonmusk) December 21, 2022
According to Musk, the sun is green. But what is happening here? Most people would say that the sun is clearly yellow just by looking at it briefly (please don’t stare at the sun). But like Rayleigh scattering, things get more complicated than basic science usually tells us.
Most of us probably know that various colors comprise white light, and probably relate that fact to the rainbow and the classic acronym “ROY G. BIV.” The sun itself emits light in a “full-body spectrum,” that is…light made up of wavelengths beyond what we humans see in a rainbow. But according to NASA, the sun “… emits most of its energy around 500 nm,” which is best described as blue-green.
So there we have it, the sun emits more “blue-green” color than anything else, and therefore it must be green, right? But what about what we see? In space, if you wear a sun visor and look up at the sun, it will appear white. And on Earth, it usually appears yellow. And that brings us back to the Rayleigh scattering effect and, just as important, the nature of our eyes.
While the sun emits more “blue-green” than anything else, it still strongly emits all visible colors. Our eyes, which contain cone cell receptors for three colors, basically tell our brain, “You see a lot of all colors!” And just as our brains blend fast-moving still images into “motion video,” our brains blend all colors into white light. But that’s in space.
Here on Earth, the atmosphere changes what we see. The Rayleigh scattering effect describes how our planet’s atmosphere scatters light, and it does so most effectively at shorter wavelengths. Blue is among the shortest wavelengths, and is therefore more predominantly scattered than most other visible colors. When sunlight hits our eyes, the lack of blue (and violet) gives us an impression of yellow.
In fact, the wavelength of violet is even shorter than that of blue. So the extra hard question is, why is the sky blue and not purple? And that has a lot to do with the fact that our eyes see blue better than violet and that the sun emits more blue than violet. Those two together combine to give the impression of a blue sky. Or simply because: the air is blue.
So what color is the sun? Is it green since it emits more green light than other colors? Is it white, as it appears to us in space? Or yellow, as it appears in the sun. If you ask NASA, the answer is: yes. All three are correct. Or at least, you can reasonably argue for either position:
So, you see, there is no simple answer to this question, but the good news is that you can defend almost any answer!
It’s all a matter of, literally, perspective.
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