Did you ever look up into the sky on a perfectly clear day and wonder why the sky above us is such a beautiful shade of blue? Most of us have wondered this. But most of us don’t think about the fact that there really isn’t a “sky” that has a blue color.
How does the Sun’s bright, warm light, which is actually white, produce the colors we see in the sky, or any of the objects on Earth for that matter? To get to the bottom of this we have to understand that all of the natural light from the sun is actually made up of a range of colors. This is what we see in a rainbow or when we see light that separates through a prism, for example.
Though light does travel in straight lines when it is interrupted by something it is actually made up of waves that vary in length. Our eyes see different colors, depending on the overall length of these waves. For example, when we see colors on the blue end of the spectrum we are experiencing shorter light waves. Light waves in the red area of the spectrum are longer than the blue waves.
Light will continue to travel on a straight path until it is stopped or re-directed. Of course, a mirror does this, as does a prism. Ordinary objects are also intercepting light. The atmosphere above us also has a unique effect on the white light of the Sun. Various gases in the atmosphere help scatter light from the Sun.
This is the basic reason for the “blue” sky we see. The blue waves of the light spectrum go in almost every direction when they contact the different molecules in our atmosphere. The other colors – reds, yellows, violets etc. – aren’t spread around as much as the blue waves.
Of course the sky can appear as different shades of blue. We see the deeper blues above us, where the air is generally thinner. The blue light isn’t “diluted” by molecules of the many gases that make up our atmosphere. Near the Earth, the air is a bit “thicker” and the blue light is widely scattered until it appears as a lighter blue or even white.
Some people have grown up with the notion that the sky is blue because it is reflecting the ocean’s color. But this is not the basic reason for the color we see. We also have to think of what the term “sky” means. The only solid objects above us are the tiny gas molecules that we don’t see and the large objects – stars – that we can sometimes see. There is no solid “bowl” of sky that is actually colored blue, by the ocean or for any other reason.
We might see reds and yellows at sunset, near the Earth. This is because of the molecules of gases, pollution etc. that re-direct the Sun’s light and allow us to see different colors. The waves of blue light are completely scattered while other colors remain visible to us.