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.)
Questions or comments regarding this lesson plan? Contact Dr.
Elizabeth Roettger
Last update: 09 Nov 1998, EER
URL: http://www.nthelp.com/eer/AENblueskyn.html