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A cloudy glass of water

A cloudy glass of water

You can see for yourself that blue light scatters more than red light. This is the same way that John Tyndall showed why the sky was blue in 1859. Fill a drinking glass with water, and then add two spoonfuls of milk – almond milk is okay if you are dairy-free – to make the water just a little milky. Now turn out the lights, draw the curtains, and shine a strong LED white flashlight towards the side of the glass of water. The one on a cellphone will work great.

If you look at the glass from the top, the light you see will seem bluish – that’s the milk molecules scattering the short waves of blue light.

But if you look at the light coming out the other side of the glass, away from the flashlight, it will seem reddish, because it is missing the blue light that has been scattered.

Why is the sky blue?
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