Why is the sky and water blue? We take it for granted that on a sunny day the sky is blue. Have you ever wondered why the sky is blue? When we drink a glass of water it looks clear and colorless but why does a lake or ocean look blue? My favorite color is blue so lets learn something about light…
White light contains all the colors of the rainbow.
Sunlight is made up of many colors but it looks white if all the wavelengths of light are together. When sunlight enters the atmosphere, particles in the air scatter blue light so that the sky looks blue.
In 1871, Lord Rayleigh discovered that light scatters from atmospheric particles like nitrogen and oxygen which are smaller than the wavelength of light hitting them.
This effect is called Rayleigh scattering and shows that short wavelengths like blue and violet have more energy and scatter a lot more.
This scattering of blue light goes evenly in all directions. If we look directly at the sun, we would see more white light wavelengths, because light would be reaching our eyes directly.
But. when we look away from the sun we see the shorter scattered wavelengths of blue and violet. Also it seems that our eyes are more sensitive to blue light than to the lighter violet light.
Yes, you are correct, the sky is bluer in some parts of the world. The reason is because of air pollution, altitude, latitude and moisture.
Industrial areas like eastern China and eastern United States have more air pollution and skies are less blue. Mountain areas of western North America are higher in elevation so the skies are darker blue. Hot coastal areas have lots of humidity and skies are less blue.
The bluest skies in the world are in New Zealand, Australia, South Africa and some northern regions in Canada and South America.
It seems that distilled water is clear and colorless. But, why does water look blue?
It’s true that water looks colorless but in large quantities it has a blue tinge. If you fill your bathtub with water it has a blue shade.
Lakes and oceans will have a dark blue color because of Rayleigh scattering. But absorption of light in water is a larger factor. When sunlight hits water it absorbs the reds, yellows and greens leaving the blue and violet colors.
In some warm ocean islands the shallow water combined with the white reflecting sand leaves the water a light green-blue color as in the Caribbean.
One other factor is the amount of chlorophyll and plankton in the water. These compounds increase scattering and absorb more blue light making the water appear greener.
This small article was about light and the color blue.
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Erik has a BSc degree and is a retired professional photographer who is now a published Author of many books. His passion is understanding how life and the universe works. He is currently blogging about the science of the Big Bang and the science of cosmology. Erik is helping his tribe with questions about the universe. His goal is to help find a theory of everything (TOE). In order to do that, he is trying to prove light has mass and that the fabric of spacetime is a false theory. We are welcoming questions and answers that you might have about the universe.