Glue Stick Sunset

As the day ends, the sky is painted with all sorts of beautiful colors. But why isn’t the sky red and orange during the rest of the day? Why are the colors less vibrant the further they are from the horizon? This activity will help students understand the answer to these questions.

Materials

  • Mini flashlight or pen light
  • Two to four hot glue sticks
  • Optional-White background (paper, wall, cloth)
  • Clear tape

Directions

  1. Tape the ends of the hot glue sticks together
  2. Hold your flashlight close to one end of the glue sticks. Laying it on a white surface will help see the color better.
  3. Notice the color difference between the ends of the hot glue sticks. Contemplate why this happens.

Explanation

The sun gives off white light which is made up of every color in the rainbow. Those colors are organized from highest to shortest wavelength, making blue and violet the colors with the shortest wavelength. The shorter the wavelength of the light, the more it is scattered as it interacts with the atmosphere. Because blue has such a short wavelength, it is scattered about ten times more than red light. Now you may ask why it is that the sky isn’t violet. The answer is that the sun gives much more blue light than violet light, so you can’t see it. Similarly, the hot glue stick end closest to your flashlight should be a whitish-blue color.

The reason why the sky is red during the sunset is because light takes a longer path through the atmosphere when it is on the horizon than when it is directly overhead. By that time it gets to your eyes, most of the light is scattered out and you could see the colors with higher wavelengths. This is why the color of the glue sticks gets more yellow the further it goes.