Science with Samantha

Science With Samantha: Why Is the Sky Blue?

Sept. 9, 2020

NBCUniversal, Inc.

Materials needed:

  • A clear tub filled with water
  • A little bit of milk
  • Flashlight (or cellphone)

You will need to do this experiment in a room where you can turn the lights off.

Dump a few drops of milk into your tub of water. Shine a flashlight directly overhead. What color do you see?

Do the same thing with the flashlight towards the side. Do you see the water change color?

This is a fun experiment to demonstrate why the sky is blue and why it seems to change color during sunrise or sunset. 

Why is the sky blue? Gases and particles in Earth's atmosphere scatter sunlight in all directions. Blue light is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.

As the sun sets and gets lower in the sky, its light passes through more of the atmosphere to reach you. Even more of the blue and violet light is scattered, allowing the reds and yellows to pass straight through to your eyes without all that competition from the blues.

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