Title says it all.
In: Earth Science
So, if you want a likely more correct explanation with animations, [this](https://www.youtube.com/watch?v=4HBuHX4-VU8) is the video for you. But here’s my attempt at testing my understanding.
It’s because of Rayleigh scattering. But that in itself isn’t helpful.
There’s more blue light scattered than others, to simply put. Yeah, but how? Because oxygen and nitrogen, major components of the atmosphere, “prefer” them.
Want the details? Well first, when you emit light on to an atom, the electrons do things:
1. absorb it and go to a higher energy level (it jumps to the next orbital)
2. absorb it and release it as heat (kinetic energy)
3. not absorb it
For 1 and 2 to happen, the light needs to have an exact amount of energy, not too high, not too low. That’s because only electrons with a certain amount of energy can exist in an orbital (it’s not quite the same, but think of the rings you see in those atom models. Electrons can jump to the next ring only if it has a certain amount of energy). For 3, as well, it’s not quite simple.
(Light is energy. For visible light, the higher the frequency, the higher the energy level, and the color will be more violet. Search: “electromagnetic spectrum” for diagram)
Light can be represented as an electromagnetic wave, or in another way, a disturbance in the electromagnetic field. Electrons can be in the same way as well. When a light wave passes an electron, the electron wiggles! Light and electron exist in the same field, so of course, it can interact in some way (remember, electrons aren’t absorbing them though). But, that wiggling causes the electron to emit their own light (Think about it, it goes up and down: it’s waving). The light goes in different directions: it scatters.
That emitted light has the same frequency (=energy or color) as the one it caused to wiggle. (A blue light causes the electron to wiggle. That electron will emit the same blue light.) That light is the important bit.
Now, for the electron in oxygen and nitrogen to go to a higher energy level, they need to absorb light in the ultraviolet range (we can’t see them). Anything except that specific light will not be absorbed (i.e will cause the electron to wiggle). The closer the light is to that desired energy level (for oxygen ultraviolet), the more light the electron emits. That means, electrons in oxygen will emit more light when it interacts with blue light than red light (blue light is closer to ultraviolet). Wola! The atmosphere prefers to scatter more blue light than red.
If you change oxygen and nitrogen with something else, say carbon dioxide, the sky will be a different color.
Side note. This only happens in the upper atmosphere. When molecules and atoms are close to each other (so near the surface), all the light cancels out each other except in one direction: the direction that the original sunlight is moving (from the sun to the surface).
Hope I got it mostly correct…
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