Notes for: Why the Sky is Blue

PROCEDURE

• Show an example of the blue sky model, pointing out the curve of the Earth and sky. (Note that the thickness of the atmosphere is greatly exaggerated. The atmosphere, compared to the whole earth, is about as thick as an apple's skin compared to the whole apple.)
• Explain/ask/discuss how white light is a mix of colors. Discuss the color of the sky during the day (blue to blue-white, usually) and near sunrise or sunset (orange or reddish).
• If using mini-maglight, focus it so the light spot is about the same size as the end of the glue stick.
• Darken the room. (Very dark is best.)
• Shine the flashlight straight at the house. Ask what color the light looks. (It should look white. If it doesn't, you might need fresh batteries.) Explain that the flashlight is simply white light, just like the light coming from our Sun.
• Shine the light through the short, vertical glue stick. (The sky should look faintly blue and the light on the house is a little bit yellow. Explanation: when the Sun is high in the sky, the light goes through only a small amount of atmosphere. Higher frequencies, like blue light, get scattered out more effectively than the lower frequencies (which mostly go straight through), so the sky looks blue and the remaining sunlight looks yellowish.)
• Shine the light through the long, horizontal stick. (The end near the flashlight should look faintly blue, but the end near the "house" should look decidedly orange or red. Explanation: the curve of the Earth and sky means the sunlight has to travel through more atmosphere to get to you. Now, almost all of the blue and much of the longer wavelengths are scattered out, and only the longest wavelengths (orange, red) reach you. The Sun looks red, and the sky often looks reddish, too.)

Last update: 09 Nov 1998, EER
URL: http://www.nthelp.com/eer/AENblueskyn.html