Why is the sky blue? Everytime I see the sky blue - so why is that?

Expert Answers

An illustration of the letter 'A' in a speech bubbles

The white light that our eyes see is actually made up of the colors of the rainbow.  Light travels in wavelengths.  The colors of light travel at different speeds and have different wavelengths.  This is called the spectrum.  To see the colors of light we need to have light travel...

Get
This Answer Now

Start your 48-hour free trial to unlock this answer and thousands more. Enjoy eNotes ad-free and cancel anytime.

Start your 48-Hour Free Trial

The white light that our eyes see is actually made up of the colors of the rainbow.  Light travels in wavelengths.  The colors of light travel at different speeds and have different wavelengths.  This is called the spectrum.  To see the colors of light we need to have light travel through a material that can break it up such as a prism or water in the atmosphere.  The color that we see in an object is the part of the light spectrum that is most scattered or reflected back to our eyes.  In the sky the atmosphere scatters the blue light of the spectrum.  So the sky looks blue to us.  At night when there is no light to scatter, the sky looks black.  This same principle is what makes the ocean look blue to us.  If you take a glass of ocean water- the water is clear.  Because the water reflects the blue part of the light spectrum, the ocean looks blue.

Approved by eNotes Editorial Team
An illustration of the letter 'A' in a speech bubbles

Do you know what a spectrum is? These are all the colours you see in a rainbow or a prism. These colours make up the varying wavelengths of white light, only we don't see them as such unless they are broken or split up through a process called 'refraction.' 

The colour something "is" is actually the colour not absorbed by an object but reflected back instead. Which colour is absorbed or reflected back depends on its particular wavelength and that wavelength's capacity to be absorbed or reflected by a particular object.

For example, when all colours are absorbed, what you see is 'black' - nothing comes back. Along with light, some heat is also absorbed. That is why a black asphalt pavement is so steaming hot on a summer day! (You can take a thermometer and verify the difference in temperature colours make by placing it on a white piece of paper, then a black one.)

So the sky is 'blue' because the wavelength of white light most easily reflected back to Earth from the atmosphere is the one corresponding to blue. As sunset approaches, these colours change as the angle of sunlight shifts, favouring the wavelength in white light corresponding more to reddish tones.(A part of this is also due to dust in the air, but this is another factor and subject!)

Does this answer your question? In short, the 'colour' you see is actually the wavelength of white light rejected by a particular surface, kind of like a ball bouncing back from off an invisible wall instead of passing right through.

Check out the references below for more information, and another experiment you can do.

Approved by eNotes Editorial Team