Why the Sky Is Blue

This experiment is especially geared toward the kiddos who like to ask “WHY” all the time ;) I’m sort of kidding - this is a great way to explain something we take for granted, regardless of your age level.

What you need:

  • flashlight

  • 2 liter bottle

  • milk (I used almond milk which worked, so I’m assuming any non-dairy milk substitute will work. If you try another kind of “milk,” let me know!)

  • water

What to do:

  • Fill the bottle about 3/4 of the way full with water

  • Prop the flashlight up so it shines through the side of the bottle

  • Add a little milk (1 tsp is the recommended amount, but I just put a splash in like how I add it to my coffee) and shake the bottle to mix. Repeat until the liquid in the bottle takes on a blue tint.

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  • Stop and observe the blue color. Then continue the process of adding milk and mixing the contents until it turns more of an orange color. Observe any other changes you see along the way.

IMG_0616.jpg

What is happening:

  • The water in your bottle is acting like the atmosphere if everything was perfect: no pollutants, clouds, or particles of any kind - just pure oxygen and nitrogen. Adding the milk simulates those other particles in the air: water vapor, carbon dioxide, dust, pollutants, etc.

  • Our atmosphere scatters more blue light than any other color because it has a smaller wavelength. That allows blue light to successfully make it through all those particles when the other colors on the visible spectrum get blocked from reaching us. The image below from NASA helps explain the different wavelengths of colors in the visible spectrum.

NASA visible wavelengths

  • As you add more milk the color turns orange. This happens around sunrise or sunset when the light is being filtered through thicker parts of the atmosphere (lower sun angle, closer to the horizon), so even more of the visible light spectrum is getting scattered.

Hannah Strong