Why is the Sky Blue?

Sunlight is riddled with colors. That’s why it’s white and why sunsets are red. Wait, what? Lemme explain.

Light from the sun is full of all the colors of the rainbow, which add up to white. Split sunlight apart, like through a prism, and you see all those colors of visible light. With that physics in mind, you’re ready to grasp why the sky is blue, and why sunsets are red.

So let’s shine a… never mind! Here you go:

Here’s a more detailed explanation:

Red and orange light have the longest wavelengths we can see. Blue and violet have the shortest wavelengths we can see.

When sunlight streams through Earth’s atmosphere—even before it reaches most clouds—it passes through a sea of air molecules that are smaller than the wavelengths of light. The longer wavelengths — reds and oranges — pass through easily. Some of the blue light makes it through, too.

But a lot of the blue light, with its short wavelength being closer to the size of the air molecules, gets reflected and redirected — scattered, as scientists put it — by those molecules. Blue light heads off in every direction, turning the sky blue. Same for violet, but the human eye doesn’t detect violet light well.