Why is the Sky Blue?

Nicole Madison
Nicole Madison

As you ponder the clear, blue sky, you may wonder just what produces such a beautiful color. The sky is not haphazardly blue; its color is no accident of nature. There is a real scientific phenomenon behind the color of the sky. The sky is blue because of a process called Rayleigh scattering. This process involves the scattering of light off of molecules in the atmosphere.

The scattering of light off of molecules in the atmosphere creates a blue sky.
The scattering of light off of molecules in the atmosphere creates a blue sky.

When light moves through the atmosphere, most of its wavelengths are able to simply pass right through. This is particularly true of its longer wavelengths. Shorter wavelengths, however, are less capable of passing through and are instead absorbed by the gas molecules in the atmosphere. It is important to understand that gas molecules absorb all colors of light; some are simply more readily absorbed than others. The sky is blue because blue light is more readily absorbed, while other wavelengths pass through easily.

To understand why the sky is blue, you must consider what happens when blue light is absorbed by gas molecules in the atmosphere. When blue light is absorbed, it is scattered in various directions, radiating throughout the sky. Since it is scattered so far and wide, the sky is blue no matter where you are positioned and where you choose to look. Sunlight consists of a full range of colors. However, the sky is blue because the efficiency with which blue light is scattered allows it to dominate what you see when you look up.

If you pay attention to the color near the horizon, you’ll notice the color there appears to be paler than the sky right above you. This is due to the fact that light, when located farther away, must pass through more air before it gets near you. Some of this distant blue light gets scattered in other directions and less of it actually reaches your line of sight. As such, although you see blue sky near the horizon, it appears pale or white.

Although the sky is blue from your position on the ground, it actually looks black from space or on the moon. Since there is no atmosphere in space, the light from the sun is not scattered and colored light doesn’t reach your eyes. Without our atmosphere, we would look up to see a black sky. Even a slightly thinner atmosphere would change our sky, making it appear a lighter blue.

Nicole Madison
Nicole Madison

Nicole’s thirst for knowledge inspired her to become a wiseGEEK writer, and she focuses primarily on topics such as homeschooling, parenting, health, science, and business. When not writing or spending time with her four children, Nicole enjoys reading, camping, and going to the beach.

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Discussion Comments


@somerset-- As far as I understand, the sea is blue for exactly the opposite reason why the sky is blue. The sky is blue because it absorbs blue color more, the sea is blue because it doesn't absorb blue color well and reflects it instead.

Sometimes the sea looks green because of the abundance of plants and other particles that may reflect green and yellow colors.


Actually scientists and doctors have shown that we see the sky as blue not only because of the wavelengths of colors and the way they are scattered, but also because of our vision and the way we perceive colors. If the issue was just about seeing the color with the shortest wavelength, then we should be seeing the sky in violet since violet has a shorter wavelength than blue. But our vision is programmed to concentrate on blue, green and red colors.

So the sky is blue because the blue wavelengths are absorbed more by the atmosphere and our eyes perceive blue more than colors of similar short wavelengths.

It's actually probably more accurate to ask "why do we see the sky as blue?" It is well known now that we do not actually see colors as realistically as we think. Even people in different parts of the world see colors slightly differently, noticing some more than others. These are believed to be genetic variations caused by survival mechanisms.


@somerset-- I have no idea. But when I was in elementary school, my teacher had told me that the sky is blue because it's the reflection of the color of seas and oceans. She said that most of the world is covered with water and that's where the sky gets its color.

Based on this article, my teacher was totally wrong and I feel so cheated right now! For more than twenty years, I believed that the sky is blue because the ocean is blue! I'm glad I looked it up though when my son asked me the same question.


@somerset -- I think it has more to do with the way the light hits the actual water and the colors scatter. In some places, like off the coast of Santa Rosa Island in Florida, the water is a jade green, regardless of the sky color. I'm not sure why it's that color there, and more of a slate blue just 30 miles to the west in Gulf Shores, Alabama. It's all the Gulf of Mexico.

I'm sure the light scattering in the atmosphere also explains why the light can turn such an odd color during an afternoon thunderstorm, or why it can look green if hail is in a storm cloud.


What I wonder is why the color changes from season to season. In the spring and summer, the sky is a paler blue, while in the autumn, the sky is a much more intense color of blue. I know it has something to do with humidity, since the higher the humidity, the lighter the blue color.

I believe in a Creator with a sense of aesthetics, so I appreciate the color of autumn leaves against a gorgeous blue sky, and I suspect He does, too. While the blue sky certainly has a scientific explanation, a Creator who is an artist had the main role in the color of the sky, in my opinion.


The blue color of the sky is reflected in the sea. I suppose that is the reason why the sea is also blue?

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