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Activity 3: Blue Sky, Red Sunset
Activity time: 18 minutes
Materials for Activity
- A large, transparent container with flat parallel sides (a 2 1/2 gallon aquarium tank is ideal)
- A flashlight
- One cup of milk in a measuring cup
- A large spatula or stirring spoon
Preparation for Activity
- Set the container on a table and fill it 3/4 full with water.
Description of Activity
This quiet, more contemplative activity helps participants recognize that while science can be exciting, it also involves reflection. Along the fine line between mystery and knowing is found the spiritual aspect of learning and discovering. Why is the sky blue, but a sunset red? This very simple experiment shows why. Hopefully, it will also evoke a sense of wonder! This experiment is used with permission from a University of Wisconsin website, Science Is Fun.
Light the flashlight and hold it against the side of the container so its beam shines through the water. Ask children to note the direction of the beam. They may be able to see some particles of floating dust, which appear white. However, it is difficult to see exactly where the beam passes through the water.
Now add 1/4 cup of milk to the water and stir it. Hold the flashlight to the side of the container, as before. Ask the children to share their observations. Affirm that the beam of light is now easily visible as it passes through the water. Look at the beam from the side (as it travels through the water) and from the end where the beam shines out of the container (looking directly toward the flashlight). From the side, the beam appears slightly blue, and on the end, it appears somewhat yellow.
Add another 1/4 cup of milk to the water and stir it. Ask the children what they see. The beam will look more blue from the side and more yellow, perhaps even orange, from the end.
Add the rest of the milk and stir. What has changed? Now the beam will look even more blue from the side. From the end, it will look orange. Furthermore, the beam seems to spread more now than it did before; it is not quite as narrow.
Process with these questions:
- What causes the beam from the flashlight to look blue from the side and orange when viewed head on? (Astronomers know that light travels in straight lines, unless it encounters the edges of a material. This is true when light travels through air, and it's true when light travels through water. Milk becomes many tiny particles suspended in the water. These particles scatter the light and make the beam visible from the side and different colors (like in a rainbow) scatter and separate, so we can see the blue and the orange light.)
- What does this experiment have to do with blue sky and orange sunsets? (The light you see when you look at the sky is sunlight that is scattered by particles of dust in the atmosphere, the same way the flashlight is scattered by particles in milk. When you look at the setting sun, it's like looking directly into the beam of the flashlight, and you see the orange and red spectrum of light.)
Make the point that knowing why light appears different-refracts differently-in different situations need not take away from our enjoyment of a sunset's beauty.
Do not let your explaining role dominate this activity. Minimize fussing with the lamp, balloon, and ball. Emphasize the children's own observations. Keep explanations short and simple. Allow silences so children can absorb what you are showing them. This is a great activity for a wide assortment of learning modalities. The challenge is to keep them from playing in the water!
Including All Participants
If the group includes a visually impaired child, verbally describe your actions and their effects at each step of this experiment.