Did someone paint the sky blue?
Today I discovered something that I absolutely have to write down in my diary. I noticed it when I looked out of the window: the sky was bright blue—not a single cloud in sight.
So I asked myself: Why is the sky blue?
It could just as easily be green like the meadow, pink like cotton candy, or yellow like the sun. But no—it’s almost always blue. Why?
At lunch, I asked Mika, “Have you ever wondered about that?”
He looked up briefly and shrugged his shoulders. “No idea,” he said, “maybe the sky is just painted like that?”
I had to laugh. But it couldn’t be that simple.
So I did some research – and the answer is really exciting!
First of all, sunlight isn’t just one color. It looks white to us, but it’s actually a mixture of many colors. Red, orange, yellow, green, blue, and violet are all hidden in sunlight, like different colored candies in a bag. Each color is like a wave that has its own properties. Some are slow and long, others short and very fast.
On its way from the sun to Earth, light has to travel through the air. And floating in this air are countless tiny particles—air molecules that we cannot see. They are so small that they act like little obstacles for the light.
And now comes the funny part:
These air particles do not collide with all colors equally. Blue light in particular – and also violet light – is pushed aside very easily. This is because blue light has very short, fast waves. The air molecules really mess up this light and send it criss-crossing through the atmosphere.
This is called scattering.
No matter which direction we look—from above, from the side, or far into the distance—blue light enters our eyes everywhere. And that’s why the whole sky looks blue to us.
“But wait,” I asked myself, “if violet light is also scattered, why isn’t the sky violet?”
This is because our eyes can see blue better than violet. In addition, a little more blue light than violet light reaches us from the sun. That’s why blue wins the color race in the end.
In the evening, something completely different happens. When the sun sets, it is no longer high above us, but very low on the horizon. The light now has to travel a much longer distance through the air. On this long journey, the blue light is scattered almost completely to the side and no longer reaches us directly.
However, the slower colors—red, orange, and yellow—still make it through the thick layer of air. They are less strongly scattered and reach our eyes. That’s why the sky often glows red, orange, or even pink at sunset.
Once I understood all this, I explained it to Mika again:
“The sky is blue because the blue light from the sun is scattered the most in the air. In the evening, almost none of it remains – then we see the red colors.”
Mika nodded slowly. “So the sky isn’t really blue,” he said, “it’s just the light being scattered around?”
“Exactly!” I replied proudly.
Since then, I’ve been looking at the sky in a completely different way. Every time I see the blue, I imagine tiny air particles playing catch with light – and how the blue light swirls through the air, laughing.
Pretty cool, right?
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Text: Lars van Gelder, Illustration: Patrizia Schoch, Translation: Fathima Cherichi Puranyil