Living in South Florida, we see an abundance of different types of clouds and skies ranging in almost all colors of the rainbow. On a clear sunny day, we see a blue sky. At sunrise and sunset we see shades of red, orange, yellow, blue and pink. Marmalade and cotton candy skies are admired by so many, yet so little of us know why the sky even changes colors. While some might think the vibrancy of our sunsets and sunrises here in South Florida are the cause of pollution, the true explanation is more scientific and less manmade. However, we first need to ask the question of why the sky is any color in the first place.
The daytime sky is seen as blue because blue light has one of the shortest visible wavelengths of the rainbow’s colors and is most sensitive to our eyes. When light passes through air filled with different kinds of particles, it changes direction and results in a phenomenon called scattering. Blue light scatters stronger than other colors because it travels in shorter, smaller waves. While violet light has the shortest wavelength, the sky is not purple because it’s wavelengths are absorbed by high atmosphere creating less violet in light. Our eyes are also less sensitive to purple due to its evolution and how we see things. All in all, it can be argued that our vision is actually subjective.
National Geographic reported that “what we see with our human eyes is just a tiny part of the electromagnetic radiation that’s given off by the sun.”
Our eyes are only sensitive to the visible wavelengths within a wide spectrum of that radiation and different wavelengths are connected to different colors. Can you imagine all the different wavelengths we can’t see? Oxygen and nitrogen, the two main molecules present in the air, preferentially scatter the shortest wavelengths: blues and purples. Yet, when sunlight travels through more of our atmosphere, we begin to see pinks and oranges.
While many have believed that pollution is causing sunrises and sunsets to be more vibrant in color, this is not entirely true. Yes, pollution causes our sunrises and sunsets to appear more red, but this pollution can either be caused by human activity or just natural aerosols created in nature. The sky’s changing colors occur because these particles either interact or destroy the natural particles in the air. When the air is clear and there are no disrupting particles, the sky at sunrise or sunset is supposed to appear yellow due to sunlight passing long distances through air and most of the blue light scattering away.
NOAA, the National Oceanic and Atmospheric Administration, states that “clean air is the main ingredient common to brightly colored sunrises and sunsets”.
Truthfully, these changes could not be visible if the sky did not appear blue in the first place. Living in South Florida and being surrounded by water, our sunsets also tend to have orange shades caused by the salt particles in the air. We also see shades of pink in our sunrises and sunsets due to dust particles in the air. The United States Geological Survey believes that this pink-sky-causing-dust is actually African dust that has periodically affected the eastern United States and the Caribbean islands due to “influxes of the airborne [particles].”
Surprisingly, the sky has also shown rare shades of green in certain parts of the world. While green skies are extremely unusual, physicist Craig Bohren of Pennsylvania State University states that “green skies are associated with severe weather.” Green skies have been seen during severe thunderstorms, tornadoes, and even hailstorms. Why this occurs has still not been entirely determined but what meteorologists and scientists do know is that it involves liquid water content in the air.
No matter what color the sky may appear, the truth is that, the position of the sun and the sky we are seeing is not entirely accurate. Fraser Cain, founder of Universe Today, did the math and it turns out that the sun and sky we see are approximately eight minutes delayed. With the sun 93 million miles away and light moving at 300,000 kilometers per second, it takes sunlight around eight minutes and 20 seconds to reach Earth. Despite not many changes occurring in this short span of time, it’s interesting to note that there is a delay.
The sky’s ranging colors are a beautiful sight to see. Whether you’re seeing a vibrant sunrise or sunset or enjoying clear, blue skies, we should be appreciative of what we see above us on a daily basis. It’s a great view when needing to relax, reflect or think things through and it’s fascinating to know that you are also, in a way, looking into the past.
