Explain · analogy · Serious version
Why the sky is blue in terms of a pinball machine
The blue colour of the sky is the result of sunlight scattering off the Earth atmosphere in a process known as Rayleigh scattering.
Imagine the Sun as the heavy metal plunger of a pinball machine, launching a high energy ball of white light towards the Earth. This white light is actually a multi coloured collection of wavelengths, ranging from long, lazy red waves to short, frantic violet ones. As the light hits the atmosphere, the gas molecules behave like those annoying little rubber bumpers that ping the ball off in random directions. The red waves are like a slow, heavy player who barely touches the bumpers, sailing straight through the mechanism without incident.
The short blue and violet waves, however, are the twitchy, caffeinated players. They hit the atmospheric nitrogen and oxygen molecules constantly, ricocheting wildly around the playfield like a ball stuck in a multiball frenzy. Because these waves are scattered in every direction, your eyes catch the blue light no matter where you look up. It is a chaotic, light speed game of pinball that has been running non stop since the dawn of the planet, ensuring that the sky maintains its familiar azure hue during the day.
When the Sun sits lower on the horizon at sunset, the light must travel through a much thicker slice of the machine. The blue light gets scattered so far off the board that it disappears into the drain, leaving only the long, red waves to reach your eyes. It is essentially the machine tilting, leaving you with nothing but the sunset.
Where the analogy breaks downThe sky does not actually have a coin slot and you cannot win a free game by hitting the troposphere.