The Sky Appears Blue Because of Something Called Scattering

Why is the sky blue? We have all heard that question hundreds of times. Many of us have asked the question numerous times. What is the response we hear most often? It is the reflection of the sunlight off the water in the oceans. However, the last time I looked at water, it was clear. Water in the oceans, depending on depth, time of day, algae content can appear many different colors, from green to black. So what is the real answer? In a word, scattering makes the sky appear blue.

Scattering

Scattering of light occurs all around us. It allows us to see color and to determine the saturation and hue of the color. The sun gives off a white light. White light can be separated into the colors of the rainbow because each of the colors has a separate wavelength and frequency. The red colored light has a long wavelength and a low frequency. Blue and violet colored light has a short wavelength and a high frequency. As the white light of the sun enters the Earth's atmosphere, it encounters molecules of oxygen (O₂) and nitrogen (N₂). As the white light hits the electrons of the oxygen and nitrogen molecules, the low frequency light gets absorbed by the molecules and the higher frequency blue and violet light bounces off the orbiting electrons. This blue light scatters in every direction, causing us to see a blue color in the sky.

Why doesn't the sky appear violet?

It is true that violet has a higher frequency than blue. Therefore, it is also true that more violet light gets scattered in the atmosphere than blue light. So, why is it that the sky does not appear violet to our eye rather than blue? We tend to see the sky as blue because our eyes are more sensitive to the colors in the middle of the color spectrum. Our eyes are able to perceive colors in the middle of the spectrum, such as yellow and green, more readily than the colors at the end of the spectrum, such as red and violet. Since blue is closer to the middle of the spectrum, our eyes see the blue scattered light better than the violet scattered light. Therefore, the sky appears blue.

Why do sunsets and sunrises appear orange or red?

During the sunrises and sunsets, the sun is closer to the horizon. The light from the sun has further to travel through the atmosphere when it is on the horizon than when it is high in the sky. The high frequency blues and violets scatter too widely when they travel that far through the atmosphere. When the light of the sun finally reaches our eyes during sunrise and sunset, the frequencies that our eyes can perceive are of lower frequency. Therefore, the light that we see is on the red and orange end of the color spectrum.