Why Is the Sky Blue?

Part One · Sunlight in the Air

Look up, but not at the sun! The sky is blue. Why is it blue, and not green or pink?

Sunlight looks white. But it is really every color of the rainbow. The colors are mixed together.

After rain, you might see a rainbow. Hold on to that: it shows the colors sunlight hides. A rainbow is sunlight spread into its colors.

Light travels in waves, like ripples on a pond. Blue ripples are close together. Red ripples are far apart.

Sunlight flies into the air around Earth. Air is full of tiny bits too small to see. They bounce the light in every direction.

Blue waves are short, so they bounce the most. Red waves are long, so they slip through.

So blue light comes from all over the sky. Look anywhere, and it finds your eyes. The whole sky looks blue.

Part Two · Violet and Sunset

Violet light bounces a lot, too. But our eyes see violet less well than blue.

At sunset, the sun is low. Its light crosses a lot of air to reach you.

On that long trip, most blue bounces away. The reds and yellows come straight to you.

So a sunset glows red and yellow. The blue did not vanish. It bounced away.

Next time the sun sets, watch the sky. Where did the blue go?