Let’s start by asking ourselves: what color SHOULD the sky be?
Or, one step further back, what color should anything be?
And the answer is: the color of anything is due to the wavelength of photons coming from that thing and hitting your eye.
Well ackshually… 🧐 These sidenotes are optional to read, but I’ll use them for giving the fuller technical details when I’ve abbreviated things in the main body of the text. In this case, the color you see is determined by the wavelengths of light entering your eye since (1) you may be seeing a pure frequency, but in almost all cases, (2) you’re seeing many frequencies, which your brain interprets as a single color. For instance, the sensation of turquoise at a specific point can be caused by (a) photons of wavelength 500nm emanating from that point, (b) a specific combo of photons of wavelengths 470nm and 540nm, or (c) (mostly realistically) photons of a huge number of wavelengths, probably peaking somewhere around 500nm. In the text, I am a bit fast and loose with the difference.
When sunlight hits Earth’s atmosphere, most colors of photons pass through unencumbered. But blue photons have a tendency to ricochet around a lot.
This causes them to disperse all throughout the atmosphere. They disperse so far and wide, and are so numerous, that you can look at any part of the sky on a clear afternoon and, at that moment, blue photons will be shooting from that point straight to your eyes.
Therefore the sky is blue.
Most colors of light pass through the atmosphere relatively unencumbered. You only see them when you look at the sun, where they contribute to the whiteness of the sun’s light. Blue, however, bounces around a lot, getting spread all over the sky. Because blue photons hit our eyeballs from every angle of the sky, the whole sky appears blue.
What’s so special about blue?
This is true and all, but it kicks the can down the road. Why blue? Why not red?
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