How to Make Your Own Blue Sky

The sky above looks blue but why is that? Beyond the sky, beyond the Earth's atmosphere is outer space, and it is black. So what makes the sky blue but space black?

In our atmosphere, there is air and dust. As sunlight shines on our planet, most of the light gets through the atmosphere. But some light bounces off of particles and it scatters. Also white light is made up from all the colors of the rainbow, mixed together. It just happens that blue light is the color of light that tends to bounce off particles and scatter. Some of that scattered blue light eventually bounces down to the ground. When you look at the sky, you see all that blue scattered light and so it makes the whole sky seem blue.

In space, it is a vacuum, there is no air and very little dust. So light doesn't have much to bounce off and just keeps traveling. Since the light just keeps going, the is no scattered light and space is dark.

You can try the following experiment to simulate the scattering effect of the Earth's atmosphere. Shine a flashlight into a tall clear glass and you will see blue late scattered to make the liquid appear blue.

1. Use a tall, small and straight sided clear jar or glass

2. Fill the container about 3/4 full with water

3. Pour in about 1/2 teaspoon of milk

4. Stir in the milk

5. Shine a strong flashlight down into the water

Observe the light from the sides of the jar and you will see that the water appears to be pale blue. The light is bouncing off the particles of milk mixed into the water. Just like with sunlight, the blue light is most likely to be reflected off of the particles and so the water appears to glow with blue light.