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What Makes the Sky Blue?

written by: Todd McCall•edited by: Jason C. Chavis•updated: 7/30/2010

Here's a detailed look at what makes the sky blue and how the Earth's atmosphere effects the visible light that reaches us from the sun.

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    Despite the fact that nearly everyone on earth walks below a blue sky nearly every day of their lives, a surprisingly small percentage of the population has a solid understandin of what makes the sky blue. Many of us grew up thinking the sky is blue due to simple explanations that were passed down to us by family members or misinformed grade school teachers. However, it turns out that the reason that sky is blue is not nearly as simple as most people think and is a direct result of the vary nature of light itself.

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    Clear Blue SkyBlue sky, mountains and waterVarying shades of blue sky at high elevation.Raleigh scattering during a sunset over the ocean
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    What Makes the Sky Blue: Modern Myths and Misunderstandings

    While modern science has provided us with an explanation for why the sky is blue, there continues to be a surprising amount of modern myths and misunderstandings surrounding this topic. For many years, public school textbooks explained to students that the sky is blue because the air in our atmosphere is actually colored blue or contains a blue substance, both of which are explanations that are offered to younger students in order to avoid a discussion of complex principles of physics. However, the true reason that the sky appears blue is actually simple enough to be explained to children with a very basic discussion of elctromagnetism and a common prism.

    Perhaps the most popular misinterpretation for what causes the sky to be blue is the modern myth that the sky is simply reflecting the color of the ocean, while the color of the sky and the ocean are actually independent of one another. While the sky does not reflect the ocean nor vica versa, both are caused by how light interacts with physical objects. In a nutshell, both the sky and large bodies of water appear blue during a clear day due to how different wavelengths of light are refracted off of natural phenomena.

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    What Makes the Sky Blue: Diffuse Sky Radiation

    The actual reason that the sky is blue is a process that causes solar radiation to be scattered as it hits Earth's atmosphere, transforming it into diffuse sky radiation. Diffuse sky radiation is the remaining solar light that is randomly scattered in the planet's upper atmosphere by hitting various molecules as light makes its way through to the surface of the Earth. The process that causes solar light to be scattered so that it appears blue in our sky is called Rayleigh scattering.

    When visible light is radiated from our sun, it starts out as basic white light. However, the various wavelengths of solar light are separated from one another by Rayleigh scattering when the radiation begins bouncing off of the molecules in our atmosphere. Much like white light that is separated into colored light by a prism, accept that the air in the Earth's atmosphere displaces considerably more short wavelength colors of light like blue rather than visible light with a larger wavelength. As a result, the sky appears blue on a clear day due to the fact that the blue light is refracted more than other solar light that is easily seen by the human eye.

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    The Sky Is Not Blue

    One of the most interesting conclusions that scientists have come to as a result of our understanding of Rayleigh scattering and diffuse sky radiation is that the sky is not primarily blue. Instead, the primary color of the sky is actually violet, but human eyesight is only barely able to perceive visible light at such a short wavelength.