Why Is the Sky Blue?

is the sky blue? That's because the solution encompasses so many components, the colors in sunlight, the angle at which solar illumination travels through the atmosphere, the size of airborne particles and atmospheric molecules, and the way our eyes perceive color. Let's take the sky out of the equation for a moment and begin by looking at color from a physics standpoint. Color refers to the wavelengths of visible light leaving an object and striking a sensor such as a human eye.

These wavelengths might be reflected or scattered from an external source, or they might emanate from the object itself. The color of an object changes depending on the colors contained in the light source. For example, red paint, when viewed under blue light, looks black. Isaac Newton demonstrated with the prism that the white light of the sun contains all colors of the visible spectrum, so all colors are possible in sunlight.

In school, you may have learned that, for example, a banana appears yellow because it reflects yellow light and absorbs all other wavelengths. This isn't quite accurate, though, a banana scatters as much orange and red as it does yellow, and it scatters all of the colors of the visible range to some degree or another. The real reason it looks yellow relates to how our eyes sense light. Before we get into that, however, let's look at what color

the sky actually is. Like bananas, atoms, molecules, and particles in the atmosphere absorb and scatter light. If they didn't, or if the Earth had no atmosphere, we would perceive the Sun as a very bright star among others in a sky of perpetual night. Not all wavelengths in the visible light spectrum scatter equally. However, shorter and more energetic wavelengths towards the violet end of the spectrum scatter better

than those towards the longer, less energetic red end. This tendency is due in part to their higher energy, which allows them to ping pong around more and in part to the geometry of the particles that they interact with in the atmosphere. In eighteen seventy one, Lord Rayleigh derived a formula describing a subset of these interactions in which atmospheric particles are much smaller than the wavelengths of the

radiation that are striking them. The Rayleigh scattering models showed that in such systems, the intensity of scattered light is inversely proportional to the fourth power of light's wavelength, which is a really Matthew way of saying that shorter wavelengths of light like blue and violet, scatter a lot more than longer redder ones when the particles that they hit,

such as oxygen and nitrogen molecules, are relatively small. Under these conditions, scattered light also tends to disperse equally in all directions, which is why the sky appears so saturated with color. If we were foolish enough to look directly at the Sun, we would see all wavelengths because light would be reaching our eyes directly. That's why the Sun

and the area around it look white. When we look away from the Sun at the cloudless sky, we see light mostly from shorter scattered wavelengths like violet, indigo, and blue. So why doesn't the sky appear violet instead of light blue? Here? The eyes have it. Your peepers perceive color using structures called cones. Your retinas bristle with about five million cones, each a made up of three types that specialize in

seeing different colors. Although each kind of cone is most sensitive to certain peak wavelengths, the ranges of those cone types overlap. As a result, different wavelengths of light and combinations of different wavelengths can be detected as the same color. Unlike our auditory senses, which can recognize individual instruments in an orchestra, our eyes and brains interpret certain combinations of

wavelengths as a single, discreet color. Our visual sense interprets the blue violet light of the sky as a mixture of blue and white light, and that is why the sky is light blue. Today's episode was written by Nicholas Garbis and produced by Tyler Clang. For more on this and lots of other curious topics, visit how stuffworks dot com. Brain Stuff is production of I Heart Radio. For more podcasts from my heart Radio, visit the heart Radio app.

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