Why Is The Sky Blue?

Friday, August 20, 2010 Aimee Larsen 1 Comments

Looking for a project to do with your kids or class that explains and shows them why our atmosphere appears blue.  Here's a fun experiment that you can do with items you already have in your home.

Purpose:  To determine why the Earth is called the blue planet

Materials:  clear drinking glass, flashlight, eyedropper, milk, spoon

  • Fill the glass with water.

  • In a darkened room, use the flashlight to direct a light beam through the center of the water.

  • Add 1 drop of milk to the water and stir.

  • Again, shine the light through the water.

Results:  The light passes through the clear water, but the milk water has a pale blue-gray look.

Why?  The waves of color in white light each have a different size.  The particles of milk in the water separate and spread the small blue waves from the light throughout the water, causing the water to appear blue.  Nitrogen and oxygen molecules in the Earth's atmosphere, like the milk particles, are small enough to separate out the small blue light waves from sunlight.  The blue light spreads out through the atmosphere, making the sky look blue from the Earth and giving the entire planet a blue look when it is observed from space.  The color in the glass is not a bright blue because more than just the blue light waves are being scattered by large particles in the milk.  This happens in the atmosphere when large quantities of dust or water vapor scatter more than just the blue light waves.  Clean, dry air produces the deepest blue sky color because the blue waves in the light are scattered the most.

1 comment:

  1. It reminds me of these two fantastic books I got for my little girl called "Why is the sky blue?" and "Do Dogs Dream?" They are great! My friend sells Learning Ladder products (which are also great!) and these books answer all of those tough questions that can be a little tricky for mum to answer. Highly recommended! Sophie



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