Why is the sky blue, and why is the sunset red?

Before I jump in — are you asking because you want to understand the physics behind it, or is there something specific that made you curious about this? Like, did you notice something about the color that seemed different or unexpected?

You've hit on exactly the right instinct — something is changing in the setup, and it's subtly elegant once you see it.

The physics of scattering doesn't flip. Blue light does scatter more throughout the day and at sunset. The key is: where are you looking, and where is the scattered light coming from?

During the day, you look up at the sky. The blue light scattering toward you comes from air directly above and around you — that's the light from the sun bouncing off molecules in every direction, and blue wins because it scatters more. You're seeing the scattered light.

At sunset, the sun is near the horizon. Now the light has to travel through way more atmosphere to reach you — it's taking a longer path through more air. As that sunlight travels through all that extra air, the blue light scatters away sideways (remember, it scatters more). By the time the direct sunlight reaches your eye, most of the blue is already scattered out and gone. What's left is the red and orange — the colors that scatter less and can make it through all that air to you directly.

So you're not looking at scattered light anymore. You're looking at the transmitted light — the stuff that made it through without scattering away. That's the flip. Same physics, different geometry.

Does that feel like it resolves the puzzle, or does something still seem off about it?

Actually, you're onto something real here — and it's a combination of all three things you mentioned, but not equally.

The main culprit, based on my memory, is that the sun actually does emit violet, but Earth's upper atmosphere absorbs a lot of it before it even reaches us and the scattering layer. So there's less violet in the sunlight hitting the lower atmosphere where we see the sky. That's a real drop in starting material.

But there's also an eye thing happening. Violet light scatters incredibly strongly — so strongly that a lot of it gets scattered way up high, and what does make it down to your eyes is scattered from farther away and dimmer by the time it reaches you. Plus your eyes are honestly just less sensitive to violet than to blue, especially when the light is dim. So even if there's violet up there, you're less likely to perceive it as a dominant color.

The wavelength rule itself isn't wrong exactly, but it's more of a rule about which direction scattering goes than a complete story about brightness. The amount of light that actually reaches your eye depends on where it scatters, how far it travels, and what your eye can pick out.

Do you know if the intensity drop in sunlight toward violet is actually significant, or am I hand-waving that part? That feels like something worth pinning down.

That's exactly right, and I like that you're leaving it open. You've nailed the core insight — the physics is constant, the geometry changes — and you've identified what's actually uncertain rather than pretending you understand something you don't.

The violet thing is a real question, not a cop-out. And it matters: it's the difference between "the simple rule explains everything" and "the simple rule is real but incomplete." You've got the first part solid.

If you ever do come back to wondering about violet, you'd know what to look for — how much the sun actually emits in violet wavelengths, and how sensitive human eyes are to it under these conditions. That's a better question than just accepting an answer you're not sure about.

Anything else about this nagging you, or does that feel like a good place to wrap this one up?