Why Is the Sky Blue? (2024)

Why Is the Sky Blue? (1)

Why Is the Sky Blue? (17)

SCIENCEEarth and Space

Have You Ever Wondered...

  • Why is the sky blue?
  • What color is sunlight?
  • Why does the sky turn red and orange at dawn and dusk?

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  • atmosphere,
  • blue,
  • color,
  • green,
  • horizon,
  • indigo,
  • light,
  • molecule,
  • orange,
  • prism,
  • red,
  • scattered,
  • science,
  • sky,
  • spectrum,
  • violet,
  • wavelength,
  • yellow

Today’s Wonder of the Day was inspired by ryan from AL. ryan Wonders, “why is the sky blue” Thanks for WONDERing with us, ryan!

The sunlight we see each day, called “white light," may appear colorless, but it is actually full of a lot of colors mixed together. This is why you see a rainbow when you shine white light through a prism. The prism separates the white light into each of its colors: red, orange, yellow, green, blue, indigo and violet.

Each of the colors is made up of its own wavelengths, kind of like a unique fingerprint. Red has the longest wavelength, violet has the shortest and all the other colors are somewhere in the middle.

When you look at an object, such as a yellow sunflower or a red wagon, the color you see is actually the color of light the object reflects to your eye. A yellow sunflower reflects yellow wavelengths while absorbing all the other colors. A red wagon, on the other hand, reflects red.

So how does the air in the sky have a color? The Earth's atmosphere is filled with gas molecules. As white light from the Sun passes through the atmosphere, colors with longer wavelengths, such as red, orange and yellow, pass through. Blue and violet wavelengths, on the other hand, are absorbed by the gas molecules and scattered across the sky. Your eye sees these reflected wavelengths as blue.

Of course, you've probably seen the sky turn brilliant shades of orange and red during a sunrise or sunset. When the Sun is low near the horizon as it rises or sets, the wavelengths have farther to go in order to reach your eyes. This causes the shorter blue wavelengths you see during the day to scatter even more, clearing the way for longer wavelengths like red and orange to reach your eyes.

Wonder What's Next?

Tomorrow’sWonder of the Day will be music to your ears!

Try It Out

Grab a friend or family member and explore one or more of the following colorful activities at home:

Fill your clear glass or jar with water and add about 1/2 to 1 teaspoon of milk powder and stir slowly. Turn off the lights and shine the flashlight on the surface of the water. Watch the water in the glass from the side near the flashlight. You may notice a bluish tinge. Now, hold the flashlight to the side of the glass and look through the water directly at the light. It will now look red. If you put the flashlight under the glass, the light will appear redder than before. Why does this work? The fat molecules from the milk powder in the water behave like air molecules. They scatter the light from the flashlight. When the light shines in the top of the glass, blue light is scattered and a bluish tinge can be seen out the sides. When you look through the water directly at the light, you peer through more of the milk fat molecules. This causes more scattering of the blue light and makes way for red wavelengths.

  • Do you think you could get used to the sky being a different color? What if you were to travel to a distant planet in another galaxy? Suppose on that planet the atmosphere bent light in different ways, leading to skies that were green or purple. How might life change? Do you think it would affect your mood? Why or why not? Take some time to imagine what it would be like to live on such a planet. Share your thoughts with your friends and family members. Do they agree? What do they think life would be like?
  • Want to experiment with light at home? Why not jump online to check out How To Create a Prism? You'll need just a few simple items, such as paper, aluminum foil and clear glass. Have fun separating light into its different colors!
  • Up for a challenge? Would you believe you can make blue skies and brilliant sunsets in a jar at home? It's true! You will need the following items:
    • clear glass jar or a drinking glass
    • water
    • milk powder
    • flashlight
    • dark room

Did you get it?

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Wonder Contributors

We’d like to thank:

Dani, Nora, Susan, madelyn and tariq
for contributing questions about today’s Wonder topic!

Keep WONDERing with us!

What are you wondering?

Wonder Words

  • blue
  • violet
  • sky
  • object
  • wagon
  • fingerprint
  • colorless
  • horizon
  • scattered
  • brilliant
  • tinge
  • atmosphere
  • molecule
  • signature
  • prism
  • indigo
  • wavelength
  • absorbed

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Why Is the Sky Blue? (2024)
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