Why is the Sky Blue? - Lesson for Kids

Instructor: April DeBord

April has taught Spanish and English as a Second Language and she has her Ed. S. in Foreign Language Education.

Why is the sky blue? It's not because a blue lava volcano erupted and painted the sky blue or because the sky ate a lot of blueberries. Come find out in this lesson on blue skies.

Blue Skies

One thing most people in the world have in common, besides breathing the same air, is that we have all seen a blue sky.

Maybe you've even heard sayings like 'clear blue sky' or songs that talk about them, such as Irving Berlin's song, 'Blue skies, smiling at me / Nothing but blue skies do I see...'

However, the reasons why the sky is blue may surprise you.

The Sun Plays an Important Part

The sun is very close to Earth, so it is a lot brighter than all of the stars (this is why you can't see stars during the day, even though they are there). And during the day we are able to see the sun as a disc-shaped object on a background of a blue sky.

Why is this? Well, in the air there are atoms, which are super-small particles, of the gases nitrogen and oxygen. These are two of the most important elements that make up the air in the sky, and they have an effect on the way we see the sky. When the white light from the sun passes through these atoms, the nitrogen and oxygen atoms cause the light to scatter.

Usually, all light goes in a straight line, unless something gets in its way and reflects it, bends it or scatters it, like the atoms in the air do to sunlight.

We know sunlight is important in seeing a blue sky because at night, when the sun isn't visible, the sky is dark. We can usually see the stars, which look like white pinpoints of light in the sky. We also see the moon, which generally appears like white on a black background. But we cannot see the blue sky at night because we can't see the sun.

Our Eyes Play an Important Part

Your eyes help you see the blue sky. Let's find out how. We can use the prism to show us how this works. See how white light goes into the prism, and as it disperses, or spreads out, we can see the colors separate.

Prism showing dispersion
A prism showing dispersion

Light travels in waves that look like ocean waves or mountains and hills. In the image of the prism, notice how the red, orange and yellow at the top spread out more. It looks like a rolling hill. There is more space between the peaks of the hills, so we say that the waves are longer. When you get to the blue and purple at the bottom it looks taller, like a mountain. There is less space between the peaks of the blue wave, meaning it is shorter.

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