Without looking (because you never should), what color is the sun? Chances are you said yellow. If you’ve ever watched a video from the ISS, you might have said white. But Elon Musk is here to tell us the sun is green. But what color is the sun, really? It’s yellow. And white. And green. No, really!
The whole topic started when someone on Twitter explained the Rayleigh scattering, the optical phenomenon that explains (in part) why the sky appears to be blue during daytime. That’s when Elon Musk weighed in to point out that asking “what color is the sun?” is a fun question.
A nice trick question is what color is the sun?
It appears white in space, but, as measured by peak photon count, it is green.
— Elon Musk (@elonmusk) December 21, 2022
According to Musk, the sun is green. But what’s going on here? Most people would say the sun is clearly yellow just from briefly looking at it (please don’t stare at the sun). But much like Rayleigh scattering, things get more complicated than even basic science usually tells us.
Most of us probably know that several colors comprise white light and probably link 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 comprised of wavelengths beyond just 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 thus must be green, right? But what about what we see? In space, if you wear a protector visor and look toward 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 importantly, the nature of our eyes.
While the sun does emit more “blue-green” than anything else, it still strongly emits all the visible colors. Our eyes, which contain three color cone cell receptors, basically tell our brain, “you see lots of every color!” And much like how our brains combine fast-moving still pictures into “moving video,” our brains merge all the colors into white light. But that’s in space.
Down here on Earth, the atmosphere changes what we see. The Rayleigh scattering effect describes how the atmosphere of our planet scatters light, and it does so more effectively at shorter wavelengths. Blue is among the shortest wavelengths and so is scattered more predominately than most other visible colors. By the time the sun’s light reaches our eyes, the lack of blue (and violet), gives us an impression of yellow.
For that matter, violet’s wavelength is even shorter than blue’s. So the extra tricky question is, why is the sky blue and not violet? And that has as much to do with the fact that our eyes are better at seeing blue than violet and that the sun emits more blue than violet. Those two together combine to give the impression of a blue sky. Or because simply: 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 seems on the sun. If you ask NASA, the answer is: yes. All three are correct. Or at least, you can reasonably argue for any of the positions:
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, quite literally, perspective.