Why is the sky blue?

Home Physics Videos Demonstration Why is the sky blue?

One of the most frequently asked questions of all time has to be "e;Why is the sky blue?"e; Using your tank full of water and a few drops of milk, you can demonstrate Rayleigh scattering. This is the scattering of electro-magnetic radiation by small particles in a gas or liquid. The visible spectrum represents a small portion of the electro-magnetic spectrum. What we perceive as white light is a combination of all visible wavelengths. The difference between the different colors, on a physical level, is that the different colors have different wavelengths and frequencies. The blue end of the spectrum has the highest frequency and the red end has the lowest frequency. The shorter wavelength blue light is more readily scattered by the atmosphere than the longer wavelength red. This scattering directs the blue waves to our eyes and makes the sky appear blue.
This can be demonstrated by shining a bright flashlight into the end of the tank of water with a small amount of milk. The blue light waves will be scattered and the tank will take on a faint blue tinge. Using a long tank, you can show the effect that causes the sky to appear orange at sunset.

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