Radiation Budget Activity: Glue Stick Sunset

Grade Level: 5-8

National Science Content Standards

Description of Activity

Why is the sky blue? Why do sunrise and sunset have different colors?

Materials

1. Flashlight or penlight (a regular flashlight can also be used, but its larger beam of light doesn't work as well)
2. 4 to 6 glue sticks (must be the clear ones used in glue guns)
3. White background (paper, wall, or cloth)
4. Transparent tape

Procedures

1. Using one glue stick, shine the small light into one end and hold the other end of the glue stick approximately one centimeter (less than 1/2 inch from the white background -- the end of the glue stick closer to the flashlight is a different color (bluish) than the end nearer the white background (yellowish). Notice the color of the circle on the white background.

2. Place two glue sticks end to end, and tape them together with the clear tape. Repeat step one, and notice any difference in the colors along the glue sticks and in the colored circle on the white background.

3. Repeat with 3 and then 4 glue sticks.

4. Notice the change in color on the white background.

5. Why?

Results and Discussion

The flashlight emits white light. The glue stick scatters the blue light out of the flashlight beam more than the yellow or the red light.

The first color to be scattered is blue: the end of the glue stick nearest the flashlight appears blue and the other end is yellow to yellow-orange.

As glue sticks are joined to increase the length, more yellow light is scattered and the colored circle changes to an orange color.

This demonstration shows why the sky is blue and sunsets are red. The sky is blue because blue light is most readily scattered from sunlight in the atmosphere, just as blue light was most readily scattered from white light in the glue sticks. If blue light was not scattered in the atmosphere, the Sun would look a little less yellow and a little more white, and the rest of the sky would be black. At sunset, the Sun is low near the horizon, and light travels through a greater thickness of atmosphere before reaching your eyes than it does when the sun is higher in the sky. Just as the light traveling along the glue sticks got redder as the length of the glue stick path got longer, so the sunset is red when the atmospheric path through which the sunlight travels gets longer. The scattering that produces the red sunset may be enhanced by pollution or other atmospheric conditions.

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