Why does the sky look blue on a clear day? Sunlight appears white but contains every color mixed together. Each color travels as a wave with a different length.
When sunlight enters the atmosphere, gas molecules scatter blue light much more than red. Blue has a shorter wavelength and bounces around more easily. This process is called Rayleigh scattering. The scattered blue light reaches your eyes from every direction overhead.
You can see this effect at home. Add a little milk to a glass of water and shine a flashlight through it. The water looks bluish from the side and reddish when you look straight at the light.
Sunlight appears white but contains every color mixed together, each traveling as a wave with a different length. Blue has a shorter wavelength and bounces around more easily when it hits gas molecules in the atmosphere. You can see this effect at home: add a little milk to a glass of water and shine a flashlight through it. The water looks bluish from the side and reddish when you look straight at the light — the same pattern that makes the sky blue overhead.
Blue light has a shorter wavelength than red, so it bounces off gas molecules in the atmosphere more easily. You can see this effect at home. Add a little milk to a glass of water and shine a flashlight through it in a dark room. The water looks bluish from the side, where the scattered blue light reaches your eyes. Look straight at the light source and it appears reddish, because blue has already bounced away and longer wavelengths are what remain.
Sunlight looks white, but it contains every color mixed together, each traveling as a wave with a different length. When sunlight enters the atmosphere, gas molecules scatter blue light much more than red because blue has a shorter wavelength and bounces around more easily. As a result, scattered blue light reaches your eyes from every direction overhead. You can see this at home: add a little milk to a glass of water and shine a flashlight through it. The water looks bluish from the side, and reddish when you look straight at the light.
Method & Materials
You will fill a glass or jar with water and milk, take it into a darkened room, and observe the water in the glass from the side, the side of the glass, and the top of the glass.
You will need a clear, straight-sided drinking glass or clear plastic or glass jar, water, milk, measuring spoons, and a flashlight.
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The experiment showed that when light passes through the air, some of the blue light is scattered all around the sky. This is why the sky looks blue. The experiment also showed that when the light shines in the top of the glass, the water looks blue because you see blue light scattered to the side. When you look through the water directly at the light, it appears red because some of the blue was removed by scattering.
Why do this project?
This science project is interesting and unique because it allows students to observe the same phenomenon that causes the sky to be blue in a controlled environment.
Also Consider
Experiment variations to consider include using different liquids in the jar, such as oil or juice, or using different colors of light, such as red or green.
Full project details
Additional information and source material for this project are available below.
