Look up on a sunny day and the sky is blue. But sunlight is not blue — it is white. So where does the blue come from?

White light is actually all the colors mixed together, like a crayon box melted into one beam. When sunlight hits the air, it crashes into tiny bits of gas. Blue light is small and bouncy, so it scatters and bounces all over the sky. Red and orange light are bigger and lazier, so they mostly go straight.

All that bouncing blue light comes at your eyes from every direction — and that is why the whole sky looks blue. At sunset, the light has to travel through much more air, the blue gets bounced away before it reaches you, and the lazy reds and oranges finally get their moment. That is why sunsets glow.

Try this: ask a grown-up for a glass of water and a tiny drop of milk, then shine a flashlight through it. The milky water looks blue from the side and orange from the front — a sunset in a cup.