Why is the Sky Blue?
Why is the sky blue? A question that seems so simple yet very few people can accurately answer it or answer it at all for that matter. So this article will tell you the real reason of why the sky is blue. It will also hold the truth behind sunsets and sunrises being red, yellow, and orange and more.
When I ask people why they think the sky is blue they generally tell me they don’t know or that it is a reflection of the ocean. This is not correct and here is why. The first reason is, the ocean and the sky aren’t the same color. Now in some places in the world they might look the same, but that leads me to my next point: the ocean isn’t the same color around the world and the sky is really similar. My final point here: why the ocean? Where there is light and objects there is reflection. That means everything reflects light. So why isn’t the sky the color of what’s beneath it? That can be answered easily. The sky’s color is not a reflection of any thing.
So, if the sky’s color is not a reflection, what is it? The simple answer is the molecules in the sky scatter blue light from the sun more than other colors. Let’s take a look at what that means. To do that we first have to understand some fundamentals of light. The spectrum of visible light is all the colors of light. The colors are ordered from longest wavelength to shortest wavelength. The order is: red, orange, yellow, green, blue, indigo and violet (a good memory trick for this is ROY G. BiV; indigo is lowercase because it often isn’t visible in rainbows). Blue light has one of the shortest wavelengths. As it is traveling that means it hits more particles and bounces off of them in other directions. Like two basket balls hitting each other. That is how scattering works. You might be thinking well then shouldn’t the sky be violet because violet has the shortest wave length. To explain that you have to know the sun does not emit the same amount of each color of light and some is absorbed in the atmosphere. So first of all, there is less violet light. That combined with the fact that our eyes are less sensitive to violet light makes it so we don’t see the sky as violet.
You might have noticed that if you look up at a clear sky it is blue but as you go down closer to the horizon the sky becomes closer to white. Why is this? It is caused by the light scattering and rescattering back together and combining with the other colors of light. This makes the sky a lighter blue or even white at the horizon.
So then why are sunsets red, orange, and a little yellow? As the sun gets lower in the sky the light it emits has to pass through more of the atmosphere. So the shorter wavelength light must pass through more particles so it scatters more to a point where we can’t see it anymore. The longer wavelength light scatters less, but still some. Those colors listed at the beginning of the paragraph are all colors with longer wavelengths. That’s why sunsets and sunrises are those colors.
You may be wondering why the things talked about in the previous two paragraph seem to go against each other. I’ll give you this image to refer to because the concepts are easier to understand with it. This should go without saying, but the image is not to scale. It is still a good model.
The light scatters more when heading to the person on top of the Earth, because it is traveling through more particles. This person is also the one seeing the sunset. So the light is even more scattered causing the light to be all over the place and not together so the light is not white. Therefore the longer wavelength light is the light we see most prominently.
There you go, that is most of things you might want to know about the color of the sky.
NASA page on why the sky is blue