Why is the sky blue?
Why is the sky blue? It seems silly to ask that now that we’ve been seeing the sky everyday for several years, but when we were still relatively ‘new’ to the Earth as young children, it was one question that came into our minds whenever we looked up at the sky above.
All colors are (in scientific terms!) merely absorbed frequencies. Therefore, the sky must appear blue because the frequency for blue is being somehow absorbed and radiated. Blue has a much higher frequency than colors like red, yellow or orange. As a result, these colors pass through without being radiated, but blue and its shades get scattered due to the Rayleigh Scattering effect. The atmosphere, of course, envelops the Earth, and so wherever we look aside from the Earth’s surface, we see the atmosphere…and the atmosphere radiates blue, so voila! The sky is blue.
However, you may still be wondering why the sky is not blue all the time, and why different ‘parts’ of the sky have different shading. This is a viable question, because when you take each color to have a precise frequency, and only that particular frequency is absorbed by a uniform atmosphere, then the shade should be constant everywhere, and all the time. But the answer to this is quite simple, and it actually does make sense, as few things in science make sense for science-disoriented persons!
You might have noticed that the sky gets lighter nearer to the horizon. This is due to the fact the sunlight is then penetrating the atmosphere at an angle, which means it is obstructed by much more matter. As a result, the light is scattered much more and appears to be lighter in color. At night, the sun is not visible from our particular location, and there is no light, which is why we bifurcate our time into waking time and dormant time, as before fire was invented, our eyesight and our activities were completely dependent on the presence of sunlight. The absence of light waves means that no light is present to be scattered, and as a result, we see the “black” sky. Whatever light is present in the sky is either sunlight reflected by the moon, or it is the reflection of the electric lights by the atmosphere’s gases.
If the moonlight is merely reflected sunlight, why does it appear to be white, and why does the sun seem yellow? The answer, again, lies in the scattering of light. The sun only appears yellow from Earth. Elsewhere in the Universe, due to the absence of an atmosphere, it appears white. The Earth’s atmosphere removes the shorter wavelength rays through scattering (like blue), and the rest remain concentrated in the path of light. These remaining colors together are what we have named “yellow.”
The sky, however, is much more multifaceted than simply black and blue, as anyone who watches the sunset can see. The colors are spectacular, although it is easy to see that they are all similar in shade—which means they must be similar in frequency. In fact, as the sun sinks lower, the angle again means that the sun is further away (which is why it is chilly after sundown), and therefore the light must travel a greater distance. As more light is scattered, the sun becomes less bright and seems to merge with the sky, going from yellow to orange to red. The sky, likewise, only radiates the longer wavelengths as so much of the blue, green and indigo is scattered. The more dust particles, or the more water vapor there is in the sky, the more the colors are scattered, and thus the color display is much more diverse in polluted areas and on humid days.
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