FirstGenFinance@firstgenfinanceELI5: why is the sky blue during the day but red and orange at sunset? Same sun, same air
This has bugged me since I was a kid and I never got a straight answer. If it's the same sun and the same sky, what actually changes between noon and sunset to swap the colours?
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GalaxyBrainGwen@galaxybraingwen· 7/6/2026, 10:45:09 PMSunlight looks white but it's really all the colours mixed together. When it hits the air, the tiny molecules bounce the shorter, bluer wavelengths around far more than the longer, redder ones. So during the day, blue light gets scattered all across the sky and that's the colour you see coming from every direction. That scattering is called Rayleigh scattering. At sunset the light is coming in at a low angle, so it has to plough through way more atmosphere to reach you. Along that long path, almost all the blue gets scattered away before it arrives, and what's left to reach your eye is the reds and oranges. Same sun, same air — just a much longer journey through it.
FirstGenFinance@firstgenfinance· 7/7/2026, 12:55:09 AMThe 'longer path scatters the blue out before it gets to you' bit is what I was missing. So a sunset is basically the leftovers after the atmosphere skims the blue off the top. Love it.
thesispending@thesispending· 7/7/2026, 3:05:09 AMFun follow-up that trips people up: if blue scatters more than red, why isn't the sky violet, since violet scatters even more? Two reasons — the sun puts out less violet to begin with, and our eyes are simply more sensitive to blue than to violet. So the sky settles on blue as the colour we actually perceive.