Introduction
How many of us have been asked this question by our children, or, better yet, have wondered it ourselves? How many of us had an answer better than "Because the sun paints it blue as it goes across the sky"? It's a tough question to answer because the answer is not as easy as we would like. With an easy experiment, however, we can begin to understand exactly why our daytime sky is such a wonderful blue and why our days begin and end in red.Procedure
- Gather these items from your home or workplace:
- a clear glass container, about the size of a pitcher (clear plastic can be used, too, but glass works best)
- a flashlight
- some milk or cream
- some hard candy
- a hammer
- Fill the container with water and add a few drops of the milk. Mix the milk in completely.
- If using skim milk, use more drops than usual. Make sure the water is milky enough so that it's hard to see through the water.
- Shine the flashlight or another directed beam of white light into one side of the container. Look at the water at a 90° angle from the light beam. Does the water seem a different color? To make a comparison, shine the flashlight away from
the container for a moment and shine it back in, all the while looking at the milky water. Do you see a change in the color of the water?
- Now try looking through the container directly at the incoming light beam. Is there a difference in color compared to when looking from the side? If you are having trouble seeing any change in colors, try putting more drops of milk in the water.
White Powder - White Clouds
A cloud is a tenuous collection of individual water droplets many times the wavelength of light in size. To determine the particle size where a collection becomes a white powder, take a colored hard candy and smash it with a hammer. When you have a pile of both white particles and particles of the color of the original candy, measure the white particles' size with your B optical magnifier (from your Optics Kit) and compare it to the width of a human hair. Are the white particles larger or smaller than a hair?
So what does this have to do with the blue sky, red sunsets, and white clouds?
Find out at the Blue Sky Readings.
Page authored by ACEPT W3 Group
Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504
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Last modified 15 December 1999
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Activities