Explain · analogy · Like I'm five version
Why the sky is blue in terms of a pinball machine
The sky looks blue because the air acts like a giant, invisible pinball machine for the light from the sun.
Sunlight is made of all the colours of the rainbow, but they are all jumbled together in a bright white ball. When this white light hits the gases and tiny bits of dust high up in the air, the game begins. Red and yellow lights are like big, heavy pinballs that roll right through the gaps in the air bits without hitting much at all. They just carry on straight towards the ground, which is why the sun looks white or yellow to us when it is high in the sky.
Blue light, however, is tiny and zippy, just like a silver ball being flicked around a machine. Because the blue bits are smaller, they constantly crash into the air molecules and bounce off in every direction. This is called scattering, and it turns the whole sky into a blue bouncy castle. It is like the air is constantly hitting the blue ball with flippers, spreading that colour all across your view until you cannot see anything else.
By the time you look up, the blue light has been pinged and bumped all over the place. The sky stays blue because the air is always playing this noisy game with the light rays, keeping them busy until the sun goes down. Once the sun is low, the light has to travel through more air, and the blue balls get lost in the game, letting the red ones through at last.
Where the analogy breaks downAir molecules do not have flippers to control where the light goes.