Why is the sky blue?
The short answer
Sunlight holds every colour, but air scatters short blue waves far more than long red ones. That is also why sunsets turn red.
0:28ScienceBeginnerlightRayleigh scatteringatmosphere
Chapters and transcript
- 0:00
Sunlight is every colour mixed
White sunlight contains every colour of the rainbow. Red light travels in long waves; blue light in short waves.
- 0:07
Air scatters blue far more than red
The tiny molecules in air scatter short waves much more strongly than long ones. This is Rayleigh scattering, and it sends blue light off in every direction several times more than red.
- 0:14
Blue reaches you from all over the sky
That scattered blue light arrives at your eyes from every part of the sky, so the whole sky looks blue, not only the patch around the Sun.
- 0:21
At sunset, light crosses much more air
When the Sun is low its light travels through far more air. Most of the blue is scattered away on the way, leaving the reds and oranges of a sunset.