Why the Sky is Blue

WHAT TO DO

Pick up the flashlight with the single glue stick. Turn it on by clicking the end like a pen. Look at the glue stick. What color appears to be closer to the light source? What color appears farther away? Cup your hand around the glue stick, it may help you see the colors more clearly.

Now pick up the red MagLite. This MagLite has three glue sticks of different lengths attached to it, and they are covered up so you can only see the tops. Look at the tops of the glue sticks (you can do this by looking inside the black tube). Which glue stick is the most red? Which one is the most yellow?

HOW IT WORKS

The flashlight emits white light. White light is made up of red, orange, yellow, green, blue and violet light. Blue is the first color to scatter. When you look at the side of the glue stick, you see scattered light and when you look at the end of the glue stick you see what is left. That is why the stick appears to be blue close to the light source. The next color to be scattered is yellow, as the glue stick becomes longer more and more yellow light is scattered and therefore the end of the glue stick appears red.

The sky works the same way. Blue light is more readily scattered which is why the sky appears blue during the day. Looking up at the sky is like looking at the side of the glue stick, so you see the blue scattered light. Looking at the sun however is like looking at the end of the glue stick, which is why you see yellow! When the sun is setting, the light has to travel through a greater amount of atmosphere before reaching you. You can picture the sun as the flashlight and the atmosphere the length of the glue stick. The more atmosphere the light travels through the more red the light appears.

Source:

http://www.exploratorium.edu/snacks/glue_stick/index.html