ABCs of DEW Software Investigation 8-3:

The Color of the Sky

Use Digital Cameras to Study the Color of the Sky

Let’s look more closely at the composition of the color of the sky as a result of the scattering of light.



Materials

• Digital camera to take pictures of the sky, or use the many sky photos available at the PicturePost website (go to the “Looking Up” folder for each post).

• ColorPicture software allows you to separate the layers of color in a digital photograph. Download the software and see a brief tutorial.



What To Do:

-Use a digital camera to take pictures of the sky during midday and at either sunrise or sunset, or use the many sky photos available online.

-Open ColorPicture software and, starting with the midday photo, open the digital photos of the sky that you obtained.

-Move the cursor into the image and notice the color of the highlighted pixel is displayed.

Color photograph of the sky using a camera with a fish-eye lens (which allows most of the sky to be seen at once), followed by the red, green, and blue layers of the photograph. Use ColorPicture software to separate the layers of colors in digital photographs and study the results. Picture is courtesy of Chuck Wilcox at the Museum of Science, Boston.

-Turn layers of color on and off to study the colors across the image more efficiently.



Questions

 With filter Photo of sky with a yellow filter (blocks blue light)
Without filter Photo of sky without a filter

Which of the three-color components (red, green, or blue) is dominant in the sky?

Which color contributes the least intensity to the sky? (See the contribution of a color by setting all of the computer display colors to a single picture color).

If the sky is blue because of tiny atmospheric particles scattering blue light, why is the Sun yellow?

If the Sun appears to be yellow, why do clouds appear so white in the image?

If you were riding on a satellite thousands of miles above the Earth, what would be the color of the “sky” (or outer space) and what would be the color of sunlight?

See Forrest Mims's calibrated haze sensor that is based on measuring the color of the sky at http://haze.concord.org



Extensions

• Study sky color over the course of a day or a week and note the change in the proportions of red, green, and blue light. Relate this to humidity and air pollution. For air pollution data, see the AirNow website.

• Use colored filters, simiilar to the gels used in the plant stress detection filters, and place over the camera lens and photograph the sky (see example below). For ordering filters, see the sources for equipment page.



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