All objects have the ability to either absorb or reflect light. Different materials will absorb different amounts of light and reflect the rest. Now you may wonder why the sea looks blue but a bucket of water is transparent. Or why the sky above you looks blue but the air around you is transparent.
Why is the sea blue?
In order to completely understand why this happens, you must remember that an object seems to be a specific color because it absorbs all the colors of the visible spectrum except for the color it appears to be. This means that water reflects blue light and absorbs all the rest. Some areas of the sea sometimes appear green but that has to do with how shallow that part is. As you travel deeper under sea you will find that at about 46 meters, most of the blue light is replaced with pitch darkness.
Why is the sky blue?
The sea and other water bodies are large masses of water contained by catchments in the land whereas the sky is all around us. Even the sky, like the sea appears to be many different shades of blue. You can make this comparison because the same effect that takes place in the sea is what makes the sky blue. The trillions upon trillions of water droplets in the atmosphere reflect the blue wavelength of the sun’s rays while absorbing all the rest.
The reason that a bucket of water and the air around us seem clear and transparent is because light is able to penetrate completely through these particles. The quantity of water or air which we are observing is not enough to demonstrate this effect. Doesn’t it make you wonder if only one of them is actually blue and the other one is cheating?
Collect different colored cellophane papers and use them to look at the sky (and sea if possible) what do you notice with the different colors? Does the outcome of your observations change at sunrise and sunset?
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