Why Is the Sky Blue Instead of Red?

Imagine sunlight is a stream of colorful balls rolling through the air. The air is full of tiny invisible particles called molecules. When these balls hit the molecules, they bounce off in all directions.

Blue balls are small and energetic, so they get bounced around a lot more than red balls. Red balls are bigger and smoother, so they keep rolling straight through without stopping. Because there is lots of blue light bouncing everywhere around us, our eyes see a blue sky when we look up.

When the sun goes down, its light has to travel through more air to reach your eyes. By that time, almost all the bouncy blue light has scattered away. The strong red balls are left standing, which is why the sunset looks orange and red.