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Why is the sky blue? The answer, my friend, lies in a glass of clean water.

Try this experiment to answer what is one the signature questions of childhood (and how many adults really, truly know the answer?).

The answer involves using a flashlight in a dark room, which brings some drama to the question and a setting sure to invite cosmic speculation on the part of all those participating.

• A clear drinking glass
• A bit of milk
• A measuring spoon
• A flashlight
• A darkened room

1. Fill the glass about 2/3 full of water
2. Add 1/2 to 1 teaspoon milk and stir.
3. Take the glass and flashlight into a darkened room.
4. Hold the flashlight above the surface of the water and observe the water in the glass from the side. It should have a slight bluish tint.
5. Now, hold the flashlight to the side of the glass and look through the water directly at the light. The water should have a slightly reddish tint. Put the flashlight under the glass and look down into the water from the top. It should have a deeper reddish tint.

What happened:

The small particles of milk scattered the light from the flashlight, like the dust particles and molecules in the air scatter sunlight. When the light shines in the top of the glass, the water looks blue because you see blue light scattered to the side. When you look through the water directly at the light, it appears red because some of the blue was removed by scattering.