Why is the Sky Blue?

A bright blue sky above the land

Read about how light and air make the daytime sky look blue.

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Words to Know　読む前に知っておきたい言葉

You may want to read these words before you begin.

WordEnglish explanation日本語
airwhat is around us and what people and animals breathe空気
skythe space above Earth that we see when we look up空
abovein or at a higher place上に、上方に
spreadto move or reach in many directions over a wide area広がる、広げる
Earththe planet where people, animals, and plants live地球
everywherein or to every placeどこでも、至る所に
hitto touch something with force while moving当たる、ぶつかる
beautifulvery pleasing to see, hear, or experience美しい
directionsthe different ways or paths in which something can move方向
fillsmakes a space full満たす、いっぱいにする

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Have you ever asked yourself why the sky has its color during the day? It seems like a simple question, but the answer is quite interesting. It is all about light and air.

Light from above looks one way to us. But this light is actually made of many different colors. You can see all these colors when it rains and the light comes through water. We call this a rainbow. There are many colors. All these colors move together through space to reach Earth.

When light comes to Earth, it must go through air. Our air is made of many very small bits. These bits are so small that we cannot see them. But they are there all around us.

When light hits these small bits of air, something happens. The light begins to move in different ways. Some colors of light move through the air easily. They can go through without much change. But the color blue is different. This color hits the small bits and goes in many different directions. It moves up, down, left, and right. This color spreads everywhere.

Because this color spreads so much, it fills the whole sky. When you look up during the day, you see this color coming from everywhere above you. This is why the sky looks the way it does when there is much light.

But why does the sky not look this way all the time? When the day starts and when it ends, the sky can be different colors. This happens because light must go through much more air to reach your eyes. The blue color spreads so much that it goes away. Only other colors can make it through all that air. This is why we see beautiful colors like red and orange at these times.

The next time you look at the sky, remember: you are seeing light that has come far and spread through tiny bits of air above you.

Take a moment to think about what you read.

Optional: Check your understanding

You can answer these five quick questions, or skip them and choose another story.

1. What is light from above actually made of?

  1. Many different colors
  2. Only blue and white
  3. Small bits of water
  4. Air and clouds

2. What is our air made of?

  1. Only blue light
  2. Many very small bits
  3. Large drops of water
  4. Red and orange colors

3. What happens to blue light when it hits small bits of air?

  1. It stops moving.
  2. It becomes water.
  3. It spreads in many directions.
  4. It moves only toward Earth.

4. Why can the sky look red or orange when the day starts or ends?

  1. There is no air at those times.
  2. Light must travel through much more air.
  3. The sun makes new colors.
  4. Blue light becomes red.

5. What is the main idea of the reading?

  1. The sky is blue because blue light spreads through tiny bits of air.
  2. The sky always has the same color.
  3. Rainbows make the daytime sky blue.
  4. Air is made only of light.
Show answers
  1. A — Many different colors
  2. B — Many very small bits
  3. C — It spreads in many directions.
  4. B — Light must travel through much more air.
  5. A — The sky is blue because blue light spreads through tiny bits of air.

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