Okay so there’s lots of particles in the atmosphere, the sun shines white light, the light gets scattered and depending on the angle, the sky gets its color. But like, how?
In: Physics
Think of rays of light from the sun as being packets that contain a mix of colors. (This isn’t really how it works but it simplifies the picture.) When one of these packets enters your eye, you see the average of all the colors in the packet.
Packets from the Sun contain all the colors in equal amounts(for our purposes). If it’s high in the sky, looking straight at it will give you all of the colors. So the Sun looks white.
But the Sun isn’t shining only at you. There are countless rays taking countless paths through the sky, and only a tiny fraction of them hit you directly.
Raleigh scattering is an effect that more or less means that as light passes through air, it has a tendency to get knocked off of its straight line course. And it happens to have a preference for knocking blue light more than any other color. For us, we can think of it like our rainbow light packet is slowly “bleeding off” its blue light as it travels through the air. Or like it’s being run past a kind of imaginary sandpaper that prefers to scrape off blue light. The farther the packet goes through air, the more light that gets bled off. That bled off blue light gets thrown out in a random direction.
Since Raleigh scattering is occuring everywhere in the sky, all the time, some of it is bound to randomly fly in your direction and hit your eye. That is why the sky is blue. You’re basically getting some of the blue light shavings of all the light from the Sun that *didn’t* hit you.
But if this “blue light bleeding” behavior affects all light from the Sun, shouldn’t it affect the light that *does* directly hit you, too? Yes! The light streaming into your eye is having the blue shaved out of it just like all the other light. But this effect is very gradual, and related to how far that light had to travel. If the Sun is overhead, light’s path to you takes a relatively short path through air, so not much blue light has managed to escape, so you don’t really notice.
If it’s sunrise or sunset, the light is passing through the atmosphere at a lower angle. That means its path through the air is longer now, meaning more blue light gets scraped away. At some point, so much of the bluer light has been scraped away that only reddish light remains. That redder light scatters too, just not as much as the bluer light, so if you look in the direction of the sun at sunrise or sunset, that light looks red. All the blue light has been scraped out of your sunset to make the sky blue for someone else beyond the horizon.
The only major inaccuracy with this is that there’s no such thing as a “rainbow packet” of light that can have some colors “scraped out of it”. What’s really going on is that there are a zillion rays, each with one unique color, and blue rays tend to get knocked around more often. But pretending like it’s just one packet representing the sum of all colors present means less to keep track of.
Latest Answers