Explain · Serious version
Why the sky is blue in terms of a football crowd
The sky appears blue because sunlight hits the atmosphere and scatters in all directions, with the shorter blue wavelengths bouncing off gas molecules more effectively than other colours.
This process is essentially a football crowd in the upper stands when a goal is scored. Sunlight is the ball entering the stadium, a fast-moving package of energy that arrives at the atmosphere, which acts like a densely packed terrace of supporters. Once the light hits the molecules, it is deflected away from its original path, much like a ball being kicked into the crowd.
Blue light is the rowdy fan near the front who is remarkably good at catching things and throwing them everywhere. Because blue wavelengths are short and punchy, they interact more frequently with the oxygen and nitrogen molecules in the air. While red light is the sedate fan near the back who barely notices the action, blue light is being passed from person to person, creating a scattered, colourful scene that reaches our eyes from every corner of the sky.
This scattering is why the horizon looks paler and the zenith remains a deeper shade of blue. When the sun is lower, the light must travel through more of the crowd to reach you, meaning the blue light has been cheered away or spilled out of the stadium entirely before it lands. You are left with the lingering, low-energy red waves, which explains the sunset.
Where the analogy breaks downthe atmosphere does not become unruly, demand a half-time pie or attempt to invade the pitch after the sun goes down.