What is scattering?
Scattering of light happens when light hits tiny particles — such as gas molecules, dust or water droplets — and spreads out in many directions. Unlike reflection from a smooth mirror, scattering sends light all over the place. Scattering explains many things we see in the sky.
Key idea
Small particles scatter blue light more than red light. That is why the daytime sky looks blue.
Why the sky is blue
Sunlight contains all colours. As it passes through the atmosphere, tiny gas particles scatter the blue light much more than the red light. This scattered blue light reaches our eyes from all over the sky, so the sky looks blue during the day.
Red sunsets
At sunset the Sun is low, so its light travels through more air to reach us. Most of the blue light is scattered away, and mainly the red and orange light passes straight through. That is why the sky near the setting Sun looks red or orange.
Example
On a foggy day, car headlights look hazy because the water droplets in the fog scatter the light in all directions.
Remember
- Scattering spreads light in many directions.
- Blue light is scattered more than red light.
- Blue sky by day, red sky at sunset.