Earth & Space
Why is the sky blue?
Puschel looks for a blue paint pot and finds a question about light.
The short answer
Sunlight contains many colours. Air particles scatter shorter-wavelength light especially strongly in different directions. We perceive much of this scattered daylight as blue. The sky is not a painted blue surface.
An imagined Wusel scene
Puschel and Flauschi investigate
They sit on the meadow bench and look at sky beside the clouds. Puschel“Who painted the big blue?”
Flauschi“It is not paint on a ceiling. Tiny particles in air send sunlight in different directions.”
Puschel“And more blue reaches our eyes?” Flauschi“Blue light scatters more strongly than red. That makes clear sky look blue to us.”
Puschel keeps looking away from the Sun. Puschel“A paint pot would have a lot of work here.”
Flauschi smiles. Clouds drift onwards and both describe what they see. They do not need to follow sunbeams to explore the question.
Little Wusel quiz
Is blue sky a solid blue ceiling?
Choose one answer: a), b).
- a)Yes.
- b)No, it comes from scattered light.
Show answer
Correct answer: b): No, it comes from scattered light. No. Light is scattered in air.
Which light scatters more strongly in air?
Choose one answer: a), b).
- a)Blue more than red.
- b)Red more than blue.
Show answer
Correct answer: a): Blue more than red. Blue light scatters more strongly than red.
Explore in more detail
Here you will find longer explanations and further details. You can explore them together.
Understand step by step
How it works – simply explained
White light contains colours
Sunlight combines several visible colours that can be separated appropriately.
Air spreads light
Tiny air particles redirect light. Blue is scattered more strongly than red, reaching our eyes from different sky directions.
A long path changes colour
Low sunlight passes through more air. Much blue is scattered out of its direct path, so light near the Sun may look reddish. Never stare at the Sun.
Why air is not blue paint
Air is not a transparent pot of blue paint. It scatters sunlight, redirecting it. Visible blue light scatters more strongly than red, so your eyes receive blue from many directions. Low sunlight travels through more air and may appear differently coloured. This concerns an ordinary clear daytime sky, not every cloud or weather condition.
References for this explanation: [1]
The key points again
Discovery 1
Sunlight contains different colours together in white light.
Source: [1]
Discovery 2
Tiny particles in air send light in different directions. This is called scattering. Blue light scatters more strongly than red, so a clear daytime sky usually looks blue to us.
Source: [1]
Discovery 3
When the Sun is low, its light travels a longer way through air. Much blue light is scattered along the way, and the sky near the Sun can look reddish.
Source: [1]